[PATCH v16 00/20] unwind_deferred: Implement sframe handling

[PATCH v16 00/20] unwind_deferred: Implement sframe handling

[Jens Remus]

This is the implementation of parsing the SFrame V3 stack trace information
from an .sframe section in an ELF file.  It's a continuation of Josh's and
Steve's work that can be found here:

   https://lore.kernel.org/all/cover.1737511963.git.jpoimboe@kernel.org/
   https://lore.kernel.org/all/20250827201548.448472904@kernel.org/

Currently the only way to get a user space stack trace from a stack
walk (and not just copying large amount of user stack into the kernel
ring buffer) is to use frame pointers. This has a few issues. The biggest
one is that compiling frame pointers into every application and library
has been shown to cause performance overhead.

Another issue is that the format of the frames may not always be consistent
between different compilers and some architectures (s390) has no defined
format to do a reliable stack walk. The only way to perform user space
profiling on these architectures is to copy the user stack into the kernel
buffer.

SFrame [1] is now supported in binutils (x86-64, ARM64, and s390). There is
discussions going on about supporting SFrame in LLVM. SFrame acts more like
ORC, and lives in the ELF executable file as its own section. Like ORC it
has two tables where the first table is sorted by instruction pointers (IP)
and using the current IP and finding it's entry in the first table, it will
take you to the second table which will tell you where the return address
of the current function is located and then you can use that address to
look it up in the first table to find the return address of that function,
and so on. This performs a user space stack walk.

Now because the .sframe section lives in the ELF file it needs to be faulted
into memory when it is used. This means that walking the user space stack
requires being in a faultable context. As profilers like perf request a stack
trace in interrupt or NMI context, it cannot do the walking when it is
requested. Instead it must be deferred until it is safe to fault in user
space. One place this is known to be safe is when the task is about to return
back to user space.

This series makes the deferred unwind user code implement SFrame format V3
and enables it on x86-64.

[1]: https://sourceware.org/binutils/wiki/sframe


This series applies on top of v7.1-rc4 tag:

  git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git  v7.1-rc4

The to be stack-traced user space programs (and libraries) need to be
built with the recent SFrame stack trace information format V3, as
generated by binutils 2.46+ with assembler option --gsframe-3.

Namhyung Kim's related perf tools deferred callchain support can be used
for testing ("perf record --call-graph fp,defer" and "perf report/script").


Changes in v16 (see patch notes for details):
- Address Sashiko AI review feedback.
- Move SRCU definitions between patches.
- __read_fre(): Convert user read access to scope-based cleanup.
- sframe_validate_section(): Allow for a FDE[0] function start address
  of zero.
- sframe_validate_section(): Replace alternation between two FREs with
  simpler logic used for FDE and use a prev_ip_off.
- dup_mmap(): Drop unnecessary CONFIG_HAVE_UNWIND_USER_SFRAME #ifdefs.
- dup_mmap(): Call sframe_dup_mm() prior to arch_dup_mmap().

Changes in v15 (see patch notes for details):
- Rebase on v7.1-rc4.
- New patch to duplicate registered .sframe section data on clone/fork.
- Address Sashiko AI review feedback:
  - Fix sframe end passed to mtree_insert_range().
  - Fix outermost frame (FRE without datawords) handling.
  - Use GFP_KERNEL_ACCOUNT instead of GFP_KERNEL.
  - Improve text/sframe section start/end validation.
  - Always use guard(srcu) when accessing struct sframe_section fields.
  - Validate FDE repetition size for PCTYPE_MASK FDEs to be non-zero to
    prevent division by zero.
  - Only add sframe for text that is PT_LOAD in addition to PF_X.
  - Use pr_debug_once() instead of WARN_ON_ONCE() to prevent user-
    triggered warning/panic.
  - Add support for SP/FP-based CFA recovery rules with
    dereferencing.
  - Reject FRE control word with reserved_p=1.
  - x86-64: Fail unwind_user_get_reg() if !user_64bit_mode().
- Validate FDE PC type for supported values (i.e. PCTYPE_INC or
  PCTYPE_MASK).
- Validate FDE function end against text end.
- Validate FDE's number of FREs to be less or equal to FDE's function
  size, as each FRE must cover at least one byte. (Indu)
- Validate FRE function offset against FDE repetition size
  for PCTYPE_MASK.
- Change type of struct sframe_fde_internal field fres_num to the one of
  struct sframe_fda_v3 field fres_num.
- Return RC of sframe_init_[cfa_]rule_data() if bad RC.
- Normalize error code usage (.sframe is removed for all but ENOENT):
  ENOENT: No sframe or no FDE for IP found
          (FDE found but no FRE found is EINVAL)
  EFAULT: Bad address
  EINVAL: Invalid input or sframe
- Build-time checks for config options:
  - 64BIT: SFrame V3 only supports 64-bit architectures.
  - HAVE_EFFICIENT_UNALIGNED_ACCESS: Unaligned access to 16/32-bit
    SFrame FRE fields and datawords using unsafe_get_user(). (Steven)
- Add pr_debug_once() when restoring CFA/FP/RA from an unsupported
  register number.

Changes in v14 (see patch notes for details):
- Rebase on v7.1-rc2.
- Correct SFRAME_V3_FDE_TYPE_MASK value.
- Fix FDE function start address check in __read_fde().
- Rename SFrame V3 definitions accoring to final specification. (Indu)
- Improve comments on why UNWIND_USER_RULE_CFA_OFFSET is not
  implemented. (Mark Rutland)
- Add/update/improve sframe debug messages.
- Add generic and arch-specific unwind_user.h to MAINTAINERS.
- Add arch-specific unwind_user_sframe.h to MAINTAINERS.

Changes in v13 (see patch notes for details):
- Add support for SFrame V3, including its new flexible FDEs.  SFrame V2
  is not supported.

Changes in v12 (see patch notes for details):
- Adjust to Peter's latest undwind user enhancements.
- Simplify logic by using an internal SFrame FDE representation, whose
  FDE function start address field is an address instead of a PC-relative
  offset (from FDE).
- Rename struct sframe_fre to sframe_fre_internal to align with
  struct sframe_fde_internal.
- Remove unused pt_regs from unwind_user_next_common() and its
  callers. (Peter)
- Simplify unwind_user_next_sframe(). (Peter)
- Fix a few checkpatch errors and warnings.
- Minor cleanups (e.g. move includes, fix indentation).

Changes in v11:
- Support for SFrame V2 PC-relative FDE function start address.
- Support for SFrame V2 representing RA undefined as indication for
  outermost frames.


Patch 1 (new in v14), as a preparatory cleanup, adds the generic and
arch-specific unwind_user.h to MAINTAINERS.

Patches 2, 5, 12, and 19 have been updated to exclusively support the
latest SFrame V3 stack trace information format, that is generated by
binutils 2.46+.  Old SFrame V2 sections get rejected with dynamic debug
message "bad/unsupported sframe header".

Patches 8 and 9 add support to unwind user (sframe) for outermost frames.

Patches 13-16 add support to unwind user (sframe) for the new SFrame V3
flexible FDEs.

Patch 17 improves the performance of searching the SFrame FRE for an IP.

Patch 18 (new in v15) duplicates registered .sframe section data on
clone/fork from the parent to the child process.

Patch 20 is for test purposes only and will get replaced by a new
syscall, that Steven is working on:
[RFC][PATCH] unwind: Add stacktrace_setup system call
https://lore.kernel.org/all/20260429114355.6c712e6a@gandalf.local.home/

Regards,
Jens


Jens Remus (9):
  unwind_user: Add generic and arch-specific headers to MAINTAINERS
  unwind_user: Stop when reaching an outermost frame
  unwind_user/sframe: Add support for outermost frame indication
  unwind_user: Enable archs that pass RA in a register
  unwind_user: Flexible FP/RA recovery rules
  unwind_user: Flexible CFA recovery rules
  unwind_user/sframe: Add support for SFrame V3 flexible FDEs
  unwind_user/sframe: Separate reading of FRE from reading of FRE data
    words
  unwind_user/sframe: Duplicate registered .sframe section data on
    clone/fork

Josh Poimboeuf (11):
  unwind_user/sframe: Add support for reading .sframe headers
  unwind_user/sframe: Store .sframe section data in per-mm maple tree
  x86/uaccess: Add unsafe_copy_from_user() implementation
  unwind_user/sframe: Add support for reading .sframe contents
  unwind_user/sframe: Detect .sframe sections in executables
  unwind_user/sframe: Wire up unwind_user to sframe
  unwind_user/sframe: Remove .sframe section on detected corruption
  unwind_user/sframe: Show file name in debug output
  unwind_user/sframe: Add .sframe validation option
  unwind_user/sframe/x86: Enable sframe unwinding on x86
  unwind_user/sframe: Add prctl() interface for registering .sframe
    sections

 MAINTAINERS                               |   4 +
 arch/Kconfig                              |  23 +
 arch/x86/Kconfig                          |   1 +
 arch/x86/include/asm/mmu.h                |   2 +-
 arch/x86/include/asm/uaccess.h            |  39 +-
 arch/x86/include/asm/unwind_user.h        |  74 +-
 arch/x86/include/asm/unwind_user_sframe.h |  12 +
 fs/binfmt_elf.c                           |  48 +-
 include/linux/mm_types.h                  |   3 +
 include/linux/sframe.h                    |  65 ++
 include/linux/unwind_user.h               |  20 +
 include/linux/unwind_user_types.h         |  50 +-
 include/uapi/linux/elf.h                  |   1 +
 include/uapi/linux/prctl.h                |   4 +
 kernel/fork.c                             |  10 +
 kernel/sys.c                              |   9 +
 kernel/unwind/Makefile                    |   3 +-
 kernel/unwind/sframe.c                    | 938 ++++++++++++++++++++++
 kernel/unwind/sframe.h                    |  88 ++
 kernel/unwind/sframe_debug.h              |  75 ++
 kernel/unwind/user.c                      | 133 ++-
 mm/init-mm.c                              |   2 +
 mm/mmap.c                                 |   5 +
 23 files changed, 1571 insertions(+), 38 deletions(-)
 create mode 100644 arch/x86/include/asm/unwind_user_sframe.h
 create mode 100644 include/linux/sframe.h
 create mode 100644 kernel/unwind/sframe.c
 create mode 100644 kernel/unwind/sframe.h
 create mode 100644 kernel/unwind/sframe_debug.h

-- 
2.51.0

[PATCH v16 01/20] unwind_user: Add generic and arch-specific headers to MAINTAINERS

[Jens Remus]

Commit 71753c6ed2bf ("unwind_user: Add user space unwinding API with
frame pointer support") introduced include/asm-generic/unwind_user.h
without adding it to MAINTAINERS, as well as any future arch-specific
versions such as the one added by commit 49cf34c0815f
("unwind_user/x86: Enable frame pointer unwinding on x86") which
introduced arch/x86/include/asm/unwind_user.h.

Suggested-by: Dylan Hatch <dylanbhatch@google.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v14:
    - New patch.

 MAINTAINERS | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index c2c6d79275c6..7434e9d7b33f 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -27874,6 +27874,8 @@ USERSPACE STACK UNWINDING
 M:	Josh Poimboeuf <jpoimboe@kernel.org>
 M:	Steven Rostedt <rostedt@goodmis.org>
 S:	Maintained
+F:	arch/*/include/asm/unwind_user.h
+F:	include/asm-generic/unwind_user.h
 F:	include/linux/unwind*.h
 F:	kernel/unwind/
 
-- 
2.51.0

[PATCH v16 02/20] unwind_user/sframe: Add support for reading .sframe headers

[Jens Remus]

From: Josh Poimboeuf <jpoimboe@kernel.org>

In preparation for unwinding user space stacks with sframe, add basic
sframe compile infrastructure and support for reading the .sframe
section header.

sframe_add_section() reads the header and unconditionally returns an
error, so it's not very useful yet.  A subsequent patch will improve
that.

Link: https://lore.kernel.org/all/f27e8463783febfa0dabb0432a3dd6be8ad98412.1737511963.git.jpoimboe@kernel.org/

[ Jens Remus: Add support for SFrame V3.  Add support for PC-relative
FDE function start offset.  Cleanup includes and indentation. ]

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v15:
    - Improve text/sframe section start/end validation. (Sashiko AI)
    - Use GFP_KERNEL_ACCOUNT instead of GFP_KERNEL (see
      memory-allocation.rst, section "Get Free Page flags"). (Sashiko AI)
    
    Changes in v14:
    - Rename SFRAME_FDE_TYPE_REGULAR to SFRAME_FDE_TYPE_DEFAULT to match
      SFrame V3 specification. (Indu)
    - Correct SFRAME_V3_FDE_TYPE_MASK value.
    
    Changes in v13:
    - Update to SFrame V3:
      - Add and use SFRAME_VERSION_3 definition.
      - Add helper macros to access SFrame V3 FDE type.
      - Rename SFRAME_FUNC_*() macros to SFRAME_FDE_*().
      - Rename SFRAME_FDE_TYPE_PC* defines to SFRAME_FDE_PCTYPE_* and
        SFRAME_FUNC_FDE_TYPE() macro to SFRAME_V3_FDE_PCTYPE().
      - Reword OFFSET to DATAWORD in SFRAME_FRE_OFFSET_{COUNT|SIZE}()
        macros.
      - Rename version-specific SFRAME_*() macros to SFRAME_V3_*().
      - Update struct sframe_fde and rename to sframe_fde_v3:
        - Change field start_addr from s32 to s64 and rename to
          func_start_off.
        - Change field fres_num from u32 to u16.
        - New field u8 info2.
        - Remove u16 padding field.
      - Split FDE into function descriptor entry (struct sframe_fde_v3) and
        attributes (struct sframe_fde_v3).
      - Rename macro parameter "data" to "info" to hint at fde/fre info
        word and wrap it in parenthesis.
    - Group SFRAME_* definitions so that related ones are together.
    - Reword commit message (my changes).

 MAINTAINERS            |   1 +
 arch/Kconfig           |   3 +
 include/linux/sframe.h |  37 +++++++++++
 kernel/unwind/Makefile |   3 +-
 kernel/unwind/sframe.c | 136 +++++++++++++++++++++++++++++++++++++++++
 kernel/unwind/sframe.h |  81 ++++++++++++++++++++++++
 6 files changed, 260 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/sframe.h
 create mode 100644 kernel/unwind/sframe.c
 create mode 100644 kernel/unwind/sframe.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 7434e9d7b33f..a9b42b67a88d 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -27876,6 +27876,7 @@ M:	Steven Rostedt <rostedt@goodmis.org>
 S:	Maintained
 F:	arch/*/include/asm/unwind_user.h
 F:	include/asm-generic/unwind_user.h
+F:	include/linux/sframe.h
 F:	include/linux/unwind*.h
 F:	kernel/unwind/
 
diff --git a/arch/Kconfig b/arch/Kconfig
index e86880045158..94b2d5e8e529 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -486,6 +486,9 @@ config HAVE_UNWIND_USER_FP
 	bool
 	select UNWIND_USER
 
+config HAVE_UNWIND_USER_SFRAME
+	bool
+
 config HAVE_PERF_REGS
 	bool
 	help
diff --git a/include/linux/sframe.h b/include/linux/sframe.h
new file mode 100644
index 000000000000..0642595534f9
--- /dev/null
+++ b/include/linux/sframe.h
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_SFRAME_H
+#define _LINUX_SFRAME_H
+
+#ifdef CONFIG_HAVE_UNWIND_USER_SFRAME
+
+struct sframe_section {
+	unsigned long	sframe_start;
+	unsigned long	sframe_end;
+	unsigned long	text_start;
+	unsigned long	text_end;
+
+	unsigned long	fdes_start;
+	unsigned long	fres_start;
+	unsigned long	fres_end;
+	unsigned int	num_fdes;
+
+	signed char	ra_off;
+	signed char	fp_off;
+};
+
+extern int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
+			      unsigned long text_start, unsigned long text_end);
+extern int sframe_remove_section(unsigned long sframe_addr);
+
+#else /* !CONFIG_HAVE_UNWIND_USER_SFRAME */
+
+static inline int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
+				     unsigned long text_start, unsigned long text_end)
+{
+	return -ENOSYS;
+}
+static inline int sframe_remove_section(unsigned long sframe_addr) { return -ENOSYS; }
+
+#endif /* CONFIG_HAVE_UNWIND_USER_SFRAME */
+
+#endif /* _LINUX_SFRAME_H */
diff --git a/kernel/unwind/Makefile b/kernel/unwind/Makefile
index eae37bea54fd..146038165865 100644
--- a/kernel/unwind/Makefile
+++ b/kernel/unwind/Makefile
@@ -1 +1,2 @@
- obj-$(CONFIG_UNWIND_USER)	+= user.o deferred.o
+ obj-$(CONFIG_UNWIND_USER)		+= user.o deferred.o
+ obj-$(CONFIG_HAVE_UNWIND_USER_SFRAME)	+= sframe.o
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
new file mode 100644
index 000000000000..d24e9d4f8bef
--- /dev/null
+++ b/kernel/unwind/sframe.c
@@ -0,0 +1,136 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Userspace sframe access functions
+ */
+
+#define pr_fmt(fmt)	"sframe: " fmt
+
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/srcu.h>
+#include <linux/uaccess.h>
+#include <linux/mm.h>
+#include <linux/string_helpers.h>
+#include <linux/sframe.h>
+#include <linux/unwind_user_types.h>
+
+#include "sframe.h"
+
+#define dbg(fmt, ...)							\
+	pr_debug("%s (%d): " fmt, current->comm, current->pid, ##__VA_ARGS__)
+
+static void free_section(struct sframe_section *sec)
+{
+	kfree(sec);
+}
+
+static int sframe_read_header(struct sframe_section *sec)
+{
+	unsigned long header_end, fdes_start, fdes_end, fres_start, fres_end;
+	struct sframe_header shdr;
+	unsigned int num_fdes;
+
+	if (copy_from_user(&shdr, (void __user *)sec->sframe_start, sizeof(shdr))) {
+		dbg("header usercopy failed\n");
+		return -EFAULT;
+	}
+
+	if (shdr.preamble.magic != SFRAME_MAGIC ||
+	    shdr.preamble.version != SFRAME_VERSION_3 ||
+	    !(shdr.preamble.flags & SFRAME_F_FDE_SORTED) ||
+	    !(shdr.preamble.flags & SFRAME_F_FDE_FUNC_START_PCREL) ||
+	    shdr.auxhdr_len) {
+		dbg("bad/unsupported sframe header\n");
+		return -EINVAL;
+	}
+
+	if (!shdr.num_fdes || !shdr.num_fres) {
+		dbg("no fde/fre entries\n");
+		return -EINVAL;
+	}
+
+	header_end = sec->sframe_start + SFRAME_HEADER_SIZE(shdr);
+	if (header_end >= sec->sframe_end) {
+		dbg("header doesn't fit in section\n");
+		return -EINVAL;
+	}
+
+	num_fdes   = shdr.num_fdes;
+	fdes_start = header_end + shdr.fdes_off;
+	fdes_end   = fdes_start + (num_fdes * sizeof(struct sframe_fde_v3));
+
+	fres_start = header_end + shdr.fres_off;
+	fres_end   = fres_start + shdr.fre_len;
+
+	if (fres_start < fdes_end || fres_end > sec->sframe_end) {
+		dbg("inconsistent fde/fre offsets\n");
+		return -EINVAL;
+	}
+
+	sec->num_fdes		= num_fdes;
+	sec->fdes_start		= fdes_start;
+	sec->fres_start		= fres_start;
+	sec->fres_end		= fres_end;
+
+	sec->ra_off		= shdr.cfa_fixed_ra_offset;
+	sec->fp_off		= shdr.cfa_fixed_fp_offset;
+
+	return 0;
+}
+
+int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
+		       unsigned long text_start, unsigned long text_end)
+{
+	struct vm_area_struct *sframe_vma, *text_vma;
+	struct mm_struct *mm = current->mm;
+	struct sframe_section *sec;
+	int ret;
+
+	if (sframe_start >= sframe_end || text_start >= text_end) {
+		dbg("invalid sframe/text address\n");
+		return -EINVAL;
+	}
+
+	scoped_guard(mmap_read_lock, mm) {
+		sframe_vma = vma_lookup(mm, sframe_start);
+		if (!sframe_vma || sframe_end > sframe_vma->vm_end) {
+			dbg("bad sframe address (0x%lx - 0x%lx)\n",
+			    sframe_start, sframe_end);
+			return -EINVAL;
+		}
+
+		text_vma = vma_lookup(mm, text_start);
+		if (!text_vma ||
+		    !(text_vma->vm_flags & VM_EXEC) ||
+		    text_end > text_vma->vm_end) {
+			dbg("bad text address (0x%lx - 0x%lx)\n",
+			    text_start, text_end);
+			return -EINVAL;
+		}
+	}
+
+	sec = kzalloc(sizeof(*sec), GFP_KERNEL_ACCOUNT);
+	if (!sec)
+		return -ENOMEM;
+
+	sec->sframe_start	= sframe_start;
+	sec->sframe_end		= sframe_end;
+	sec->text_start		= text_start;
+	sec->text_end		= text_end;
+
+	ret = sframe_read_header(sec);
+	if (ret)
+		goto err_free;
+
+	/* TODO nowhere to store it yet - just free it and return an error */
+	ret = -ENOSYS;
+
+err_free:
+	free_section(sec);
+	return ret;
+}
+
+int sframe_remove_section(unsigned long sframe_start)
+{
+	return -ENOSYS;
+}
diff --git a/kernel/unwind/sframe.h b/kernel/unwind/sframe.h
new file mode 100644
index 000000000000..fc2908e92c7b
--- /dev/null
+++ b/kernel/unwind/sframe.h
@@ -0,0 +1,81 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * From https://www.sourceware.org/binutils/docs/sframe-spec.html
+ */
+#ifndef _SFRAME_H
+#define _SFRAME_H
+
+#include <linux/types.h>
+
+#define SFRAME_VERSION_1			1
+#define SFRAME_VERSION_2			2
+#define SFRAME_VERSION_3			3
+#define SFRAME_MAGIC				0xdee2
+
+#define SFRAME_F_FDE_SORTED			0x1
+#define SFRAME_F_FRAME_POINTER			0x2
+#define SFRAME_F_FDE_FUNC_START_PCREL		0x4
+
+#define SFRAME_ABI_AARCH64_ENDIAN_BIG		1
+#define SFRAME_ABI_AARCH64_ENDIAN_LITTLE	2
+#define SFRAME_ABI_AMD64_ENDIAN_LITTLE		3
+
+struct sframe_preamble {
+	u16	magic;
+	u8	version;
+	u8	flags;
+} __packed;
+
+struct sframe_header {
+	struct sframe_preamble preamble;
+	u8	abi_arch;
+	s8	cfa_fixed_fp_offset;
+	s8	cfa_fixed_ra_offset;
+	u8	auxhdr_len;
+	u32	num_fdes;
+	u32	num_fres;
+	u32	fre_len;
+	u32	fdes_off;
+	u32	fres_off;
+} __packed;
+
+#define SFRAME_HEADER_SIZE(header) \
+	((sizeof(struct sframe_header) + (header).auxhdr_len))
+
+struct sframe_fde_v3 {
+	s64	func_start_off;
+	u32	func_size;
+	u32	fres_off;
+} __packed;
+
+struct sframe_fda_v3 {
+	u16	fres_num;
+	u8	info;
+	u8	info2;
+	u8	rep_size;
+} __packed;
+
+#define SFRAME_FDE_PCTYPE_INC			0
+#define SFRAME_FDE_PCTYPE_MASK			1
+
+#define SFRAME_AARCH64_PAUTH_KEY_A		0
+#define SFRAME_AARCH64_PAUTH_KEY_B		1
+
+#define SFRAME_V3_FDE_FRE_TYPE(info)		((info) & 0xf)
+#define SFRAME_V3_FDE_PCTYPE(info)		(((info) >> 4) & 0x1)
+#define SFRAME_V3_AARCH64_FDE_PAUTH_KEY(info)	(((info) >> 5) & 0x1)
+
+#define SFRAME_FDE_TYPE_DEFAULT			0
+
+#define SFRAME_V3_FDE_TYPE_MASK			0x1f
+#define SFRAME_V3_FDE_TYPE(info2)		((info2) & SFRAME_V3_FDE_TYPE_MASK)
+
+#define SFRAME_BASE_REG_FP			0
+#define SFRAME_BASE_REG_SP			1
+
+#define SFRAME_V3_FRE_CFA_BASE_REG_ID(info)		((info) & 0x1)
+#define SFRAME_V3_FRE_DATAWORD_COUNT(info)		(((info) >> 1) & 0xf)
+#define SFRAME_V3_FRE_DATAWORD_SIZE(info)		(((info) >> 5) & 0x3)
+#define SFRAME_V3_AARCH64_FRE_MANGLED_RA_P(info)	(((info) >> 7) & 0x1)
+
+#endif /* _SFRAME_H */
-- 
2.51.0

[PATCH v16 03/20] unwind_user/sframe: Store .sframe section data in per-mm maple tree

[Jens Remus]

From: Josh Poimboeuf <jpoimboe@kernel.org>

Associate an .sframe section with its mm by adding it to a per-mm maple
tree which is indexed by the corresponding text address range.  A single
.sframe section can be associated with multiple text ranges.

[ Jens Remus: Minor cleanups. Reword commit subject/message. ]

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v16:
    - Move SRCU definitions from patch "unwind_user/sframe: Add support for
      reading .sframe contents" here. (Sashiko AI)
    
    Changes in v15:
    - Fix text section end passed to mtree_insert_range() to be inclusive.
      (Sashiko AI)
    - sframe_remove_section(): Add guard(srcu) to guard access to
      sec->sframe_start.  This also guards access to sec->filename
      in __sframe_remove_section(). (Sashiko AI)
    - Use GFP_KERNEL_ACCOUNT instead of GFP_KERNEL (see
      memory-allocation.rst, section "Get Free Page flags"). (Sashiko AI)

 arch/x86/include/asm/mmu.h |  2 +-
 include/linux/mm_types.h   |  3 ++
 include/linux/sframe.h     | 18 ++++++++++
 kernel/fork.c              | 10 ++++++
 kernel/unwind/sframe.c     | 68 ++++++++++++++++++++++++++++++++++++--
 mm/init-mm.c               |  2 ++
 6 files changed, 99 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/mmu.h b/arch/x86/include/asm/mmu.h
index 0fe9c569d171..227a32899a59 100644
--- a/arch/x86/include/asm/mmu.h
+++ b/arch/x86/include/asm/mmu.h
@@ -87,7 +87,7 @@ typedef struct {
 	.context = {							\
 		.ctx_id = 1,						\
 		.lock = __MUTEX_INITIALIZER(mm.context.lock),		\
-	}
+	},
 
 void leave_mm(void);
 #define leave_mm leave_mm
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index a308e2c23b82..c1505356b6fc 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -1424,6 +1424,9 @@ struct mm_struct {
 #ifdef CONFIG_MM_ID
 		mm_id_t mm_id;
 #endif /* CONFIG_MM_ID */
+#ifdef CONFIG_HAVE_UNWIND_USER_SFRAME
+		struct maple_tree sframe_mt;
+#endif
 	} __randomize_layout;
 
 	/*
diff --git a/include/linux/sframe.h b/include/linux/sframe.h
index 0642595534f9..38047760e252 100644
--- a/include/linux/sframe.h
+++ b/include/linux/sframe.h
@@ -2,9 +2,14 @@
 #ifndef _LINUX_SFRAME_H
 #define _LINUX_SFRAME_H
 
+#include <linux/mm_types.h>
+#include <linux/srcu.h>
+
 #ifdef CONFIG_HAVE_UNWIND_USER_SFRAME
 
 struct sframe_section {
+	struct rcu_head	rcu;
+
 	unsigned long	sframe_start;
 	unsigned long	sframe_end;
 	unsigned long	text_start;
@@ -19,18 +24,31 @@ struct sframe_section {
 	signed char	fp_off;
 };
 
+#define INIT_MM_SFRAME .sframe_mt = MTREE_INIT(sframe_mt, 0),
+extern void sframe_free_mm(struct mm_struct *mm);
+
 extern int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
 			      unsigned long text_start, unsigned long text_end);
 extern int sframe_remove_section(unsigned long sframe_addr);
 
+static inline bool current_has_sframe(void)
+{
+	struct mm_struct *mm = current->mm;
+
+	return mm && !mtree_empty(&mm->sframe_mt);
+}
+
 #else /* !CONFIG_HAVE_UNWIND_USER_SFRAME */
 
+#define INIT_MM_SFRAME
+static inline void sframe_free_mm(struct mm_struct *mm) {}
 static inline int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
 				     unsigned long text_start, unsigned long text_end)
 {
 	return -ENOSYS;
 }
 static inline int sframe_remove_section(unsigned long sframe_addr) { return -ENOSYS; }
+static inline bool current_has_sframe(void) { return false; }
 
 #endif /* CONFIG_HAVE_UNWIND_USER_SFRAME */
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 5f3fdfdb14c7..8d8195561c95 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -110,6 +110,7 @@
 #include <linux/tick.h>
 #include <linux/unwind_deferred.h>
 #include <linux/pgalloc.h>
+#include <linux/sframe.h>
 #include <linux/uaccess.h>
 
 #include <asm/mmu_context.h>
@@ -735,6 +736,7 @@ void __mmdrop(struct mm_struct *mm)
 	mm_pasid_drop(mm);
 	mm_destroy_cid(mm);
 	percpu_counter_destroy_many(mm->rss_stat, NR_MM_COUNTERS);
+	sframe_free_mm(mm);
 
 	free_mm(mm);
 }
@@ -1072,6 +1074,13 @@ static void mmap_init_lock(struct mm_struct *mm)
 #endif
 }
 
+static void mm_init_sframe(struct mm_struct *mm)
+{
+#ifdef CONFIG_HAVE_UNWIND_USER_SFRAME
+	mt_init(&mm->sframe_mt);
+#endif
+}
+
 static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
 	struct user_namespace *user_ns)
 {
@@ -1100,6 +1109,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
 	mm->pmd_huge_pte = NULL;
 #endif
 	mm_init_uprobes_state(mm);
+	mm_init_sframe(mm);
 	hugetlb_count_init(mm);
 
 	mm_flags_clear_all(mm);
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index d24e9d4f8bef..46dba3cb016d 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -19,6 +19,8 @@
 #define dbg(fmt, ...)							\
 	pr_debug("%s (%d): " fmt, current->comm, current->pid, ##__VA_ARGS__)
 
+DEFINE_STATIC_SRCU(sframe_srcu);
+
 static void free_section(struct sframe_section *sec)
 {
 	kfree(sec);
@@ -81,6 +83,7 @@ static int sframe_read_header(struct sframe_section *sec)
 int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
 		       unsigned long text_start, unsigned long text_end)
 {
+	struct maple_tree *sframe_mt = &current->mm->sframe_mt;
 	struct vm_area_struct *sframe_vma, *text_vma;
 	struct mm_struct *mm = current->mm;
 	struct sframe_section *sec;
@@ -122,15 +125,74 @@ int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
 	if (ret)
 		goto err_free;
 
-	/* TODO nowhere to store it yet - just free it and return an error */
-	ret = -ENOSYS;
+	ret = mtree_insert_range(sframe_mt, sec->text_start, sec->text_end - 1,
+				 sec, GFP_KERNEL_ACCOUNT);
+	if (ret) {
+		dbg("mtree_insert_range failed: text=%lx-%lx\n",
+		    sec->text_start, sec->text_end);
+		goto err_free;
+	}
+
+	return 0;
 
 err_free:
 	free_section(sec);
 	return ret;
 }
 
+static void sframe_free_srcu(struct rcu_head *rcu)
+{
+	struct sframe_section *sec = container_of(rcu, struct sframe_section, rcu);
+
+	free_section(sec);
+}
+
+static int __sframe_remove_section(struct mm_struct *mm,
+				   struct sframe_section *sec)
+{
+	if (!mtree_erase(&mm->sframe_mt, sec->text_start)) {
+		dbg("mtree_erase failed: text=%lx\n", sec->text_start);
+		return -EINVAL;
+	}
+
+	call_srcu(&sframe_srcu, &sec->rcu, sframe_free_srcu);
+
+	return 0;
+}
+
 int sframe_remove_section(unsigned long sframe_start)
 {
-	return -ENOSYS;
+	struct mm_struct *mm = current->mm;
+	struct sframe_section *sec;
+	unsigned long index = 0;
+	bool found = false;
+	int ret = 0;
+
+	guard(srcu)(&sframe_srcu);
+
+	mt_for_each(&mm->sframe_mt, sec, index, ULONG_MAX) {
+		if (sec->sframe_start == sframe_start) {
+			found = true;
+			ret |= __sframe_remove_section(mm, sec);
+		}
+	}
+
+	if (!found || ret)
+		return -EINVAL;
+
+	return 0;
+}
+
+void sframe_free_mm(struct mm_struct *mm)
+{
+	struct sframe_section *sec;
+	unsigned long index = 0;
+
+	if (!mm)
+		return;
+
+	mt_for_each(&mm->sframe_mt, sec, index, ULONG_MAX)
+		free_section(sec);
+
+	mtree_destroy(&mm->sframe_mt);
 }
diff --git a/mm/init-mm.c b/mm/init-mm.c
index c5556bb9d5f0..77909139162e 100644
--- a/mm/init-mm.c
+++ b/mm/init-mm.c
@@ -11,6 +11,7 @@
 #include <linux/atomic.h>
 #include <linux/user_namespace.h>
 #include <linux/iommu.h>
+#include <linux/sframe.h>
 #include <asm/mmu.h>
 
 #ifndef INIT_MM_CONTEXT
@@ -49,6 +50,7 @@ struct mm_struct init_mm = {
 #endif
 	.flexible_array	= MM_STRUCT_FLEXIBLE_ARRAY_INIT,
 	INIT_MM_CONTEXT(init_mm)
+	INIT_MM_SFRAME
 };
 
 void setup_initial_init_mm(void *start_code, void *end_code,
-- 
2.51.0

[PATCH v16 04/20] x86/uaccess: Add unsafe_copy_from_user() implementation

[Jens Remus]

From: Josh Poimboeuf <jpoimboe@kernel.org>

Add an x86 implementation of unsafe_copy_from_user() similar to the
existing unsafe_copy_to_user().

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v15:
    - unsafe_copy_from_user(): Use const void *__src. (Sashiko AI)

 arch/x86/include/asm/uaccess.h | 39 +++++++++++++++++++++++++---------
 1 file changed, 29 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 3a0dd3c2b233..235886106f31 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -598,7 +598,7 @@ _label:									\
  * We want the unsafe accessors to always be inlined and use
  * the error labels - thus the macro games.
  */
-#define unsafe_copy_loop(dst, src, len, type, label)				\
+#define unsafe_copy_to_user_loop(dst, src, len, type, label)			\
 	while (len >= sizeof(type)) {						\
 		unsafe_put_user(*(type *)(src),(type __user *)(dst),label);	\
 		dst += sizeof(type);						\
@@ -606,15 +606,34 @@ _label:									\
 		len -= sizeof(type);						\
 	}
 
-#define unsafe_copy_to_user(_dst,_src,_len,label)			\
-do {									\
-	char __user *__ucu_dst = (_dst);				\
-	const char *__ucu_src = (_src);					\
-	size_t __ucu_len = (_len);					\
-	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u64, label);	\
-	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u32, label);	\
-	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u16, label);	\
-	unsafe_copy_loop(__ucu_dst, __ucu_src, __ucu_len, u8, label);	\
+#define unsafe_copy_to_user(_dst, _src, _len, label)				\
+do {										\
+	void __user *__dst = (_dst);						\
+	const void *__src = (_src);						\
+	size_t __len = (_len);							\
+	unsafe_copy_to_user_loop(__dst, __src, __len, u64, label);		\
+	unsafe_copy_to_user_loop(__dst, __src, __len, u32, label);		\
+	unsafe_copy_to_user_loop(__dst, __src, __len, u16, label);		\
+	unsafe_copy_to_user_loop(__dst, __src, __len, u8,  label);		\
+} while (0)
+
+#define unsafe_copy_from_user_loop(dst, src, len, type, label)			\
+	while (len >= sizeof(type)) {						\
+		unsafe_get_user(*(type *)(dst), (type __user *)(src), label);	\
+		dst += sizeof(type);						\
+		src += sizeof(type);						\
+		len -= sizeof(type);						\
+	}
+
+#define unsafe_copy_from_user(_dst, _src, _len, label)				\
+do {										\
+	void *__dst = (_dst);							\
+	const void __user *__src = (_src);					\
+	size_t __len = (_len);							\
+	unsafe_copy_from_user_loop(__dst, __src, __len, u64, label);		\
+	unsafe_copy_from_user_loop(__dst, __src, __len, u32, label);		\
+	unsafe_copy_from_user_loop(__dst, __src, __len, u16, label);		\
+	unsafe_copy_from_user_loop(__dst, __src, __len, u8,  label);		\
 } while (0)
 
 #ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT
-- 
2.51.0

[PATCH v16 05/20] unwind_user/sframe: Add support for reading .sframe contents

[Jens Remus]

From: Josh Poimboeuf <jpoimboe@kernel.org>

In preparation for using sframe to unwind user space stacks, add an
sframe_find() interface for finding the sframe information associated
with a given text address.

For performance, use user_read_access_begin() and the corresponding
unsafe_*() accessors.  Note that use of pr_debug() in uaccess-enabled
regions would break noinstr validation, so there aren't any debug
messages yet.  That will be added in a subsequent commit.

Link: https://lore.kernel.org/all/77c0d1ec143bf2a53d66c4ecb190e7e0a576fbfd.1737511963.git.jpoimboe@kernel.org/
Link: https://lore.kernel.org/all/b35ca3a3-8de5-4d32-8d30-d4e562f6b0de@linux.ibm.com/

[ Jens Remus: Add initial support for SFrame V3 (limited to default
FDEs).  Add support for PC-relative FDE function start offset.  Simplify
logic by using an internal FDE representation.  Rename struct sframe_fre
to sframe_fre_internal to align with struct sframe_fde_internal.
Cleanup includes.  Fix checkpatch errors "spaces required around that
':'". ]

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v16:
    - __read_fre(): Compute FRE size before mutating dataword_count.
      (Sashiko AI)
    - __read_fre(): Convert user read access to scope-based cleanup.
      (Sashiko AI)
    - Move SRCU definitions to patch "unwind_user/sframe: Store .sframe
      section data in per-mm maple tree". (Sashiko AI)
    
    Changes in v15:
    - __read_fde():
      - Validate FDE repetition size for PCTYPE_MASK FDEs to be non-zero to
        prevent division by zero. (Sashiko AI)
      - Validate FDE PC type for supported values (i.e. PCTYPE_INC or
        PCTYPE_MASK).
      - Validate FDE function end against text end.
      - Validate FDE's number of FREs to be less or equal to FDE's function
        size, as each FRE must cover at least one byte. (Indu)
    - __read_fre(): Validate FRE function offset against FDE repetition size
      for PCTYPE_MASK.
    - Change type of struct sframe_fde_internal field fres_num to the one of
      struct sframe_fda_v3 field fres_num.
    - Normalize error code usage (.sframe is removed for all but ENOENT):
      ENOENT: No sframe or no FDE for IP found
              (FDE found but no FRE found is EINVAL)
      EFAULT: Bad address
      EINVAL: Invalid input or sframe
    - Build-time checks for config options:
      - 64BIT: SFrame V3 only supports 64-bit architectures.
      - HAVE_EFFICIENT_UNALIGNED_ACCESS: Unaligned access to 16/32-bit
        SFrame FRE fields and datawords using unsafe_get_user(). (Steven)
    - Reword my changelog in commit message.
    
    Changes in v14:
    - Fix FDE function start address check in __read_fde().
    - Adjust to rename of SFRAME_FDE_TYPE_*.
    
    Changes in v13:
    - Update to SFrame V3:
      - Adjust to SFRAME_V3_*() macros and macro/define renames.
      - Adjust to struct sframe_fde_v3 rename.
      - Adjust to s64 FDE function start offset.
      - Rename local variables fde_type to fde_pctype.
      - Add and maintain struct sframe_fde_internal field u8 info2.
      - Adjust to FDE split into function descriptor entry
        (struct sframe_fde_v3) and attributes (struct sframe_fde_v3).
      - Rename offset_count/offset_size to dataword_count/dataword_count.
      - Limit __read_fre() to SFrame V3 regular FDEs (FDE_TYPE_REGULAR).  A
        subsequent patch will add support for flexible FDEs (FDE_TYPE_FLEX).
    - Rename struct sframe_fde_internal field func_start_addr to func_addr.
    - Add support u64/s64 in UNSAFE_GET_USER_INC() for s64 FDE function
      start offset.
    - Reduce indentation of assignments to fre.
    - Reword commit message (my changes).

 include/linux/sframe.h       |   3 +
 kernel/unwind/sframe.c       | 362 ++++++++++++++++++++++++++++++++++-
 kernel/unwind/sframe_debug.h |  35 ++++
 3 files changed, 396 insertions(+), 4 deletions(-)
 create mode 100644 kernel/unwind/sframe_debug.h

diff --git a/include/linux/sframe.h b/include/linux/sframe.h
index 38047760e252..9a72209696f9 100644
--- a/include/linux/sframe.h
+++ b/include/linux/sframe.h
@@ -4,6 +4,7 @@
 
 #include <linux/mm_types.h>
 #include <linux/srcu.h>
+#include <linux/unwind_user_types.h>
 
 #ifdef CONFIG_HAVE_UNWIND_USER_SFRAME
 
@@ -30,6 +31,7 @@ extern void sframe_free_mm(struct mm_struct *mm);
 extern int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
 			      unsigned long text_start, unsigned long text_end);
 extern int sframe_remove_section(unsigned long sframe_addr);
+extern int sframe_find(unsigned long ip, struct unwind_user_frame *frame);
 
 static inline bool current_has_sframe(void)
 {
@@ -48,6 +50,7 @@ static inline int sframe_add_section(unsigned long sframe_start, unsigned long s
 	return -ENOSYS;
 }
 static inline int sframe_remove_section(unsigned long sframe_addr) { return -ENOSYS; }
+static inline int sframe_find(unsigned long ip, struct unwind_user_frame *frame) { return -ENOSYS; }
 static inline bool current_has_sframe(void) { return false; }
 
 #endif /* CONFIG_HAVE_UNWIND_USER_SFRAME */
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 46dba3cb016d..2de29c836f6b 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -15,12 +15,355 @@
 #include <linux/unwind_user_types.h>
 
 #include "sframe.h"
-
-#define dbg(fmt, ...)							\
-	pr_debug("%s (%d): " fmt, current->comm, current->pid, ##__VA_ARGS__)
+#include "sframe_debug.h"
+
+struct sframe_fde_internal {
+	unsigned long	func_addr;
+	u32		func_size;
+	u32		fda_off;
+	u32		fres_off;
+	u16		fres_num;
+	u8		info;
+	u8		info2;
+	u8		rep_size;
+};
+
+struct sframe_fre_internal {
+	unsigned int	size;
+	u32		ip_off;
+	s32		cfa_off;
+	s32		ra_off;
+	s32		fp_off;
+	u8		info;
+};
 
 DEFINE_STATIC_SRCU(sframe_srcu);
 
+static __always_inline unsigned char fre_type_to_size(unsigned char fre_type)
+{
+	if (fre_type > 2)
+		return 0;
+	return 1 << fre_type;
+}
+
+static __always_inline unsigned char dataword_size_enum_to_size(unsigned char dataword_size)
+{
+	if (dataword_size > 2)
+		return 0;
+	return 1 << dataword_size;
+}
+
+static __always_inline int __read_fde(struct sframe_section *sec,
+				      unsigned int fde_num,
+				      struct sframe_fde_internal *fde)
+{
+	unsigned long fde_addr, fda_addr, func_start, func_end;
+	struct sframe_fde_v3 _fde;
+	struct sframe_fda_v3 _fda;
+	unsigned char fde_pctype;
+
+	fde_addr = sec->fdes_start + (fde_num * sizeof(struct sframe_fde_v3));
+	unsafe_copy_from_user(&_fde, (void __user *)fde_addr,
+			      sizeof(struct sframe_fde_v3), Efault);
+
+	func_start = fde_addr + _fde.func_start_off;
+	func_end = func_start + _fde.func_size;
+	if (func_start < sec->text_start || func_end > sec->text_end)
+		return -EFAULT;
+
+	fda_addr = sec->fres_start + _fde.fres_off;
+	if (fda_addr + sizeof(struct sframe_fda_v3) > sec->fres_end)
+		return -EFAULT;
+	unsafe_copy_from_user(&_fda, (void __user *)fda_addr,
+			      sizeof(struct sframe_fda_v3), Efault);
+
+	fde_pctype = SFRAME_V3_FDE_PCTYPE(_fda.info);
+	if (fde_pctype != SFRAME_FDE_PCTYPE_INC &&
+	    fde_pctype != SFRAME_FDE_PCTYPE_MASK)
+		return -EINVAL;
+	if (fde_pctype == SFRAME_FDE_PCTYPE_MASK && !_fda.rep_size)
+		return -EINVAL;
+	if (_fda.fres_num > _fde.func_size)
+		return -EINVAL;
+
+	fde->func_addr	= func_start;
+	fde->func_size	= _fde.func_size;
+	fde->fda_off	= _fde.fres_off;
+	fde->fres_off	= _fde.fres_off + sizeof(struct sframe_fda_v3);
+	fde->fres_num	= _fda.fres_num;
+	fde->info	= _fda.info;
+	fde->info2	= _fda.info2;
+	fde->rep_size	= _fda.rep_size;
+
+	return 0;
+
+Efault:
+	return -EFAULT;
+}
+
+static __always_inline int __find_fde(struct sframe_section *sec,
+				      unsigned long ip,
+				      struct sframe_fde_internal *fde)
+{
+	unsigned long func_addr_low = 0, func_addr_high = ULONG_MAX;
+	struct sframe_fde_v3 __user *first, *low, *high, *found = NULL;
+	int ret;
+
+	first = (void __user *)sec->fdes_start;
+	low = first;
+	high = first + sec->num_fdes - 1;
+
+	while (low <= high) {
+		struct sframe_fde_v3 __user *mid;
+		s64 func_off;
+		unsigned long func_addr;
+
+		mid = low + ((high - low) / 2);
+
+		unsafe_get_user(func_off, (s64 __user *)mid, Efault);
+		func_addr = (unsigned long)mid + func_off;
+
+		if (ip >= func_addr) {
+			if (func_addr < func_addr_low)
+				return -EINVAL;
+
+			func_addr_low = func_addr;
+
+			found = mid;
+			low = mid + 1;
+		} else {
+			if (func_addr > func_addr_high)
+				return -EINVAL;
+
+			func_addr_high = func_addr;
+
+			high = mid - 1;
+		}
+	}
+
+	if (!found)
+		return -ENOENT;
+
+	ret = __read_fde(sec, found - first, fde);
+	if (ret)
+		return ret;
+
+	/* make sure it's not in a gap */
+	if (ip < fde->func_addr || ip >= fde->func_addr + fde->func_size)
+		return -ENOENT;
+
+	return 0;
+
+Efault:
+	return -EFAULT;
+}
+
+#define ____UNSAFE_GET_USER_INC(to, from, type, label)			\
+({									\
+	type __to;							\
+	unsafe_get_user(__to, (type __user *)from, label);		\
+	from += sizeof(__to);						\
+	to = __to;							\
+})
+
+#define __UNSAFE_GET_USER_INC(to, from, size, label, u_or_s)		\
+({									\
+	switch (size) {							\
+	case 1:								\
+		____UNSAFE_GET_USER_INC(to, from, u_or_s##8, label);	\
+		break;							\
+	case 2:								\
+		____UNSAFE_GET_USER_INC(to, from, u_or_s##16, label);	\
+		break;							\
+	case 4:								\
+		____UNSAFE_GET_USER_INC(to, from, u_or_s##32, label);	\
+		break;							\
+	default:							\
+		return -EFAULT;						\
+	}								\
+})
+
+#define UNSAFE_GET_USER_UNSIGNED_INC(to, from, size, label)		\
+	__UNSAFE_GET_USER_INC(to, from, size, label, u)
+
+#define UNSAFE_GET_USER_SIGNED_INC(to, from, size, label)		\
+	__UNSAFE_GET_USER_INC(to, from, size, label, s)
+
+#define UNSAFE_GET_USER_INC(to, from, size, label)				\
+	_Generic(to,								\
+		 u8 :	UNSAFE_GET_USER_UNSIGNED_INC(to, from, size, label),	\
+		 u16 :	UNSAFE_GET_USER_UNSIGNED_INC(to, from, size, label),	\
+		 u32 :	UNSAFE_GET_USER_UNSIGNED_INC(to, from, size, label),	\
+		 u64 :	UNSAFE_GET_USER_UNSIGNED_INC(to, from, size, label),	\
+		 s8 :	UNSAFE_GET_USER_SIGNED_INC(to, from, size, label),	\
+		 s16 :	UNSAFE_GET_USER_SIGNED_INC(to, from, size, label),	\
+		 s32 :	UNSAFE_GET_USER_SIGNED_INC(to, from, size, label),	\
+		 s64 :	UNSAFE_GET_USER_SIGNED_INC(to, from, size, label))
+
+static __always_inline int __read_fre(struct sframe_section *sec,
+				      struct sframe_fde_internal *fde,
+				      unsigned long fre_addr,
+				      struct sframe_fre_internal *fre)
+{
+	unsigned char fde_type = SFRAME_V3_FDE_TYPE(fde->info2);
+	unsigned char fde_pctype = SFRAME_V3_FDE_PCTYPE(fde->info);
+	unsigned char fre_type = SFRAME_V3_FDE_FRE_TYPE(fde->info);
+	unsigned char dataword_count, dataword_size;
+	s32 cfa_off, ra_off, fp_off;
+	unsigned long cur = fre_addr;
+	unsigned char addr_size;
+	unsigned int fre_size;
+	u32 ip_off;
+	u8 info;
+
+	addr_size = fre_type_to_size(fre_type);
+	if (!addr_size)
+		return -EINVAL;
+
+	if (fre_addr + addr_size + 1 > sec->fres_end)
+		return -EFAULT;
+
+	UNSAFE_GET_USER_INC(ip_off, cur, addr_size, Efault);
+	if ((fde_pctype == SFRAME_FDE_PCTYPE_INC && ip_off >= fde->func_size) ||
+	    (fde_pctype == SFRAME_FDE_PCTYPE_MASK && ip_off >= fde->rep_size))
+		return -EINVAL;
+
+	UNSAFE_GET_USER_INC(info, cur, 1, Efault);
+	dataword_count = SFRAME_V3_FRE_DATAWORD_COUNT(info);
+	dataword_size  = dataword_size_enum_to_size(SFRAME_V3_FRE_DATAWORD_SIZE(info));
+	if (!dataword_count || !dataword_size)
+		return -EINVAL;
+	fre_size = addr_size + 1 + (dataword_count * dataword_size);
+
+	if (cur + (dataword_count * dataword_size) > sec->fres_end)
+		return -EFAULT;
+
+	/* TODO: Support for flexible FDEs not implemented yet. */
+	if (fde_type != SFRAME_FDE_TYPE_DEFAULT)
+		return -EINVAL;
+
+	UNSAFE_GET_USER_INC(cfa_off, cur, dataword_size, Efault);
+	dataword_count--;
+
+	ra_off = sec->ra_off;
+	if (!ra_off) {
+		if (!dataword_count--)
+			return -EINVAL;
+
+		UNSAFE_GET_USER_INC(ra_off, cur, dataword_size, Efault);
+	}
+
+	fp_off = sec->fp_off;
+	if (!fp_off && dataword_count) {
+		dataword_count--;
+		UNSAFE_GET_USER_INC(fp_off, cur, dataword_size, Efault);
+	}
+
+	if (dataword_count)
+		return -EINVAL;
+
+	fre->size	= fre_size;
+	fre->ip_off	= ip_off;
+	fre->cfa_off	= cfa_off;
+	fre->ra_off	= ra_off;
+	fre->fp_off	= fp_off;
+	fre->info	= info;
+
+	return 0;
+
+Efault:
+	return -EFAULT;
+}
+
+static __always_inline int __find_fre(struct sframe_section *sec,
+				      struct sframe_fde_internal *fde,
+				      unsigned long ip,
+				      struct unwind_user_frame *frame)
+{
+	unsigned char fde_pctype = SFRAME_V3_FDE_PCTYPE(fde->info);
+	struct sframe_fre_internal *fre, *prev_fre = NULL;
+	struct sframe_fre_internal fres[2];
+	unsigned long fre_addr;
+	bool which = false;
+	unsigned int i;
+	u32 ip_off;
+
+	ip_off = ip - fde->func_addr;
+
+	if (fde_pctype == SFRAME_FDE_PCTYPE_MASK)
+		ip_off %= fde->rep_size;
+
+	fre_addr = sec->fres_start + fde->fres_off;
+
+	for (i = 0; i < fde->fres_num; i++) {
+		int ret;
+
+		/*
+		 * Alternate between the two fre_addr[] entries for 'fre' and
+		 * 'prev_fre'.
+		 */
+		fre = which ? fres : fres + 1;
+		which = !which;
+
+		ret = __read_fre(sec, fde, fre_addr, fre);
+		if (ret)
+			return ret;
+
+		fre_addr += fre->size;
+
+		if (prev_fre && fre->ip_off <= prev_fre->ip_off)
+			return -EINVAL;
+
+		if (fre->ip_off > ip_off)
+			break;
+
+		prev_fre = fre;
+	}
+
+	if (!prev_fre)
+		return -EINVAL;
+	fre = prev_fre;
+
+	frame->cfa_off = fre->cfa_off;
+	frame->ra_off  = fre->ra_off;
+	frame->fp_off  = fre->fp_off;
+	frame->use_fp  = SFRAME_V3_FRE_CFA_BASE_REG_ID(fre->info) == SFRAME_BASE_REG_FP;
+
+	return 0;
+}
+
+int sframe_find(unsigned long ip, struct unwind_user_frame *frame)
+{
+	struct mm_struct *mm = current->mm;
+	struct sframe_section *sec;
+	struct sframe_fde_internal fde;
+	void __user *sframe_start;
+	int ret;
+
+	if (!mm)
+		return -EINVAL;
+
+	guard(srcu)(&sframe_srcu);
+
+	sec = mtree_load(&mm->sframe_mt, ip);
+	if (!sec)
+		return -ENOENT;
+
+	sframe_start = (void __user *)sec->sframe_start;
+	scoped_user_read_access_size(sframe_start,
+				     sec->sframe_end - sec->sframe_start,
+				     Efault) {
+		ret = __find_fde(sec, ip, &fde);
+		if (!ret)
+			ret = __find_fre(sec, &fde, ip, frame);
+	}
+
+	return ret;
+
+Efault:
+	return -EFAULT;
+}
+
 static void free_section(struct sframe_section *sec)
 {
 	kfree(sec);
@@ -32,6 +375,15 @@ static int sframe_read_header(struct sframe_section *sec)
 	struct sframe_header shdr;
 	unsigned int num_fdes;
 
+	/* SFrame V3 is only supported on 64-bit architectures */
+	BUILD_BUG_ON(!IS_ENABLED(CONFIG_64BIT));
+
+	/*
+	 * Unaligned access to 16/32-bit SFrame FRE fields and datawords
+	 * using unsafe_get_user() via UNSAFE_GET_USER_INC()
+	 */
+	BUILD_BUG_ON(!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS));
+
 	if (copy_from_user(&shdr, (void __user *)sec->sframe_start, sizeof(shdr))) {
 		dbg("header usercopy failed\n");
 		return -EFAULT;
@@ -122,8 +474,10 @@ int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
 	sec->text_end		= text_end;
 
 	ret = sframe_read_header(sec);
-	if (ret)
+	if (ret) {
+		dbg_print_header(sec);
 		goto err_free;
+	}
 
 	ret = mtree_insert_range(sframe_mt, sec->text_start, sec->text_end - 1,
 				 sec, GFP_KERNEL_ACCOUNT);
diff --git a/kernel/unwind/sframe_debug.h b/kernel/unwind/sframe_debug.h
new file mode 100644
index 000000000000..36352124cde8
--- /dev/null
+++ b/kernel/unwind/sframe_debug.h
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _SFRAME_DEBUG_H
+#define _SFRAME_DEBUG_H
+
+#include <linux/sframe.h>
+#include "sframe.h"
+
+#ifdef CONFIG_DYNAMIC_DEBUG
+
+#define dbg(fmt, ...)							\
+	pr_debug("%s (%d): " fmt, current->comm, current->pid, ##__VA_ARGS__)
+
+static __always_inline void dbg_print_header(struct sframe_section *sec)
+{
+	unsigned long fdes_end;
+
+	fdes_end = sec->fdes_start + (sec->num_fdes * sizeof(struct sframe_fde_v3));
+
+	dbg("SEC: sframe:0x%lx-0x%lx text:0x%lx-0x%lx "
+	    "fdes:0x%lx-0x%lx fres:0x%lx-0x%lx "
+	    "ra_off:%d fp_off:%d\n",
+	    sec->sframe_start, sec->sframe_end, sec->text_start, sec->text_end,
+	    sec->fdes_start, fdes_end, sec->fres_start, sec->fres_end,
+	    sec->ra_off, sec->fp_off);
+}
+
+#else /* !CONFIG_DYNAMIC_DEBUG */
+
+#define dbg(args...)			no_printk(args)
+
+static inline void dbg_print_header(struct sframe_section *sec) {}
+
+#endif /* !CONFIG_DYNAMIC_DEBUG */
+
+#endif /* _SFRAME_DEBUG_H */
-- 
2.51.0

[PATCH v16 06/20] unwind_user/sframe: Detect .sframe sections in executables

[Jens Remus]

From: Josh Poimboeuf <jpoimboe@kernel.org>

When loading an ELF executable, automatically detect an .sframe section
and associate it with the mm_struct.

[ Jens Remus: Fix checkpatch warning "braces {} are not necessary for
single statement blocks". ]

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v15:
    - Only add sframe for text that is PT_LOAD in addition to PF_X.
      (Sashiko AI)

 fs/binfmt_elf.c          | 48 +++++++++++++++++++++++++++++++++++++---
 include/uapi/linux/elf.h |  1 +
 2 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 16a56b6b3f6c..980a9f229cd1 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -48,6 +48,7 @@
 #include <linux/uaccess.h>
 #include <uapi/linux/rseq.h>
 #include <linux/rseq.h>
+#include <linux/sframe.h>
 #include <asm/param.h>
 #include <asm/page.h>
 
@@ -637,6 +638,21 @@ static inline int make_prot(u32 p_flags, struct arch_elf_state *arch_state,
 	return arch_elf_adjust_prot(prot, arch_state, has_interp, is_interp);
 }
 
+static void elf_add_sframe(struct elf_phdr *text, struct elf_phdr *sframe,
+			   unsigned long base_addr)
+{
+	unsigned long sframe_start, sframe_end, text_start, text_end;
+
+	sframe_start = base_addr + sframe->p_vaddr;
+	sframe_end   = sframe_start + sframe->p_memsz;
+
+	text_start   = base_addr + text->p_vaddr;
+	text_end     = text_start + text->p_memsz;
+
+	/* Ignore return value, sframe section isn't critical */
+	sframe_add_section(sframe_start, sframe_end, text_start, text_end);
+}
+
 /* This is much more generalized than the library routine read function,
    so we keep this separate.  Technically the library read function
    is only provided so that we can read a.out libraries that have
@@ -647,7 +663,7 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
 		unsigned long no_base, struct elf_phdr *interp_elf_phdata,
 		struct arch_elf_state *arch_state)
 {
-	struct elf_phdr *eppnt;
+	struct elf_phdr *eppnt, *sframe_phdr = NULL;
 	unsigned long load_addr = 0;
 	int load_addr_set = 0;
 	unsigned long error = ~0UL;
@@ -673,7 +689,8 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
 
 	eppnt = interp_elf_phdata;
 	for (i = 0; i < interp_elf_ex->e_phnum; i++, eppnt++) {
-		if (eppnt->p_type == PT_LOAD) {
+		switch (eppnt->p_type) {
+		case PT_LOAD: {
 			int elf_type = MAP_PRIVATE;
 			int elf_prot = make_prot(eppnt->p_flags, arch_state,
 						 true, true);
@@ -712,6 +729,19 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
 				error = -ENOMEM;
 				goto out;
 			}
+			break;
+		}
+		case PT_GNU_SFRAME:
+			sframe_phdr = eppnt;
+			break;
+		}
+	}
+
+	if (sframe_phdr) {
+		eppnt = interp_elf_phdata;
+		for (i = 0; i < interp_elf_ex->e_phnum; i++, eppnt++) {
+			if (eppnt->p_flags & PF_X && eppnt->p_type == PT_LOAD)
+				elf_add_sframe(eppnt, sframe_phdr, load_addr);
 		}
 	}
 
@@ -836,7 +866,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
 	int first_pt_load = 1;
 	unsigned long error;
 	struct elf_phdr *elf_ppnt, *elf_phdata, *interp_elf_phdata = NULL;
-	struct elf_phdr *elf_property_phdata = NULL;
+	struct elf_phdr *elf_property_phdata = NULL, *sframe_phdr = NULL;
 	unsigned long elf_brk;
 	bool brk_moved = false;
 	int retval, i;
@@ -945,6 +975,10 @@ static int load_elf_binary(struct linux_binprm *bprm)
 				executable_stack = EXSTACK_DISABLE_X;
 			break;
 
+		case PT_GNU_SFRAME:
+			sframe_phdr = elf_ppnt;
+			break;
+
 		case PT_LOPROC ... PT_HIPROC:
 			retval = arch_elf_pt_proc(elf_ex, elf_ppnt,
 						  bprm->file, false,
@@ -1242,6 +1276,14 @@ static int load_elf_binary(struct linux_binprm *bprm)
 			elf_brk = k;
 	}
 
+	if (sframe_phdr) {
+		for (i = 0, elf_ppnt = elf_phdata;
+		     i < elf_ex->e_phnum; i++, elf_ppnt++) {
+			if (elf_ppnt->p_flags & PF_X && elf_ppnt->p_type == PT_LOAD)
+				elf_add_sframe(elf_ppnt, sframe_phdr, load_bias);
+		}
+	}
+
 	e_entry = elf_ex->e_entry + load_bias;
 	phdr_addr += load_bias;
 	elf_brk += load_bias;
diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index ee30dcd80901..e2a7dbed2e80 100644
--- a/include/uapi/linux/elf.h
+++ b/include/uapi/linux/elf.h
@@ -41,6 +41,7 @@ typedef __u16	Elf64_Versym;
 #define PT_GNU_STACK	(PT_LOOS + 0x474e551)
 #define PT_GNU_RELRO	(PT_LOOS + 0x474e552)
 #define PT_GNU_PROPERTY	(PT_LOOS + 0x474e553)
+#define PT_GNU_SFRAME	(PT_LOOS + 0x474e554)
 
 
 /* ARM MTE memory tag segment type */
-- 
2.51.0

[PATCH v16 07/20] unwind_user/sframe: Wire up unwind_user to sframe

[Jens Remus]

From: Josh Poimboeuf <jpoimboe@kernel.org>

Now that the sframe infrastructure is fully in place, make it work by
hooking it up to the unwind_user interface.

[ Jens Remus: Remove unused pt_regs from unwind_user_next_common() and
its callers.  Simplify unwind_user_next_sframe(). ]

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---
 arch/Kconfig                      |  1 +
 include/linux/unwind_user_types.h |  4 +++-
 kernel/unwind/user.c              | 23 +++++++++++++++++++++++
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 94b2d5e8e529..37549832bd1f 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -488,6 +488,7 @@ config HAVE_UNWIND_USER_FP
 
 config HAVE_UNWIND_USER_SFRAME
 	bool
+	select UNWIND_USER
 
 config HAVE_PERF_REGS
 	bool
diff --git a/include/linux/unwind_user_types.h b/include/linux/unwind_user_types.h
index 412729a269bc..43e4b160883f 100644
--- a/include/linux/unwind_user_types.h
+++ b/include/linux/unwind_user_types.h
@@ -9,7 +9,8 @@
  * available.
  */
 enum unwind_user_type_bits {
-	UNWIND_USER_TYPE_FP_BIT =		0,
+	UNWIND_USER_TYPE_SFRAME_BIT =		0,
+	UNWIND_USER_TYPE_FP_BIT =		1,
 
 	NR_UNWIND_USER_TYPE_BITS,
 };
@@ -17,6 +18,7 @@ enum unwind_user_type_bits {
 enum unwind_user_type {
 	/* Type "none" for the start of stack walk iteration. */
 	UNWIND_USER_TYPE_NONE =			0,
+	UNWIND_USER_TYPE_SFRAME =		BIT(UNWIND_USER_TYPE_SFRAME_BIT),
 	UNWIND_USER_TYPE_FP =			BIT(UNWIND_USER_TYPE_FP_BIT),
 };
 
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index 90ab3c1a205e..1fb272419733 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -7,6 +7,7 @@
 #include <linux/sched/task_stack.h>
 #include <linux/unwind_user.h>
 #include <linux/uaccess.h>
+#include <linux/sframe.h>
 
 #define for_each_user_frame(state) \
 	for (unwind_user_start(state); !(state)->done; unwind_user_next(state))
@@ -82,6 +83,16 @@ static int unwind_user_next_fp(struct unwind_user_state *state)
 	return unwind_user_next_common(state, &fp_frame);
 }
 
+static int unwind_user_next_sframe(struct unwind_user_state *state)
+{
+	struct unwind_user_frame frame;
+
+	/* sframe expects the frame to be local storage */
+	if (sframe_find(state->ip, &frame))
+		return -ENOENT;
+	return unwind_user_next_common(state, &frame);
+}
+
 static int unwind_user_next(struct unwind_user_state *state)
 {
 	unsigned long iter_mask = state->available_types;
@@ -95,6 +106,16 @@ static int unwind_user_next(struct unwind_user_state *state)
 
 		state->current_type = type;
 		switch (type) {
+		case UNWIND_USER_TYPE_SFRAME:
+			switch (unwind_user_next_sframe(state)) {
+			case 0:
+				return 0;
+			case -ENOENT:
+				continue;	/* Try next method. */
+			default:
+				state->done = true;
+			}
+			break;
 		case UNWIND_USER_TYPE_FP:
 			if (!unwind_user_next_fp(state))
 				return 0;
@@ -123,6 +144,8 @@ static int unwind_user_start(struct unwind_user_state *state)
 		return -EINVAL;
 	}
 
+	if (current_has_sframe())
+		state->available_types |= UNWIND_USER_TYPE_SFRAME;
 	if (IS_ENABLED(CONFIG_HAVE_UNWIND_USER_FP))
 		state->available_types |= UNWIND_USER_TYPE_FP;
 
-- 
2.51.0

[PATCH v16 08/20] unwind_user: Stop when reaching an outermost frame

[Jens Remus]

Add an indication for an outermost frame to the unwind user frame
structure and stop unwinding when reaching an outermost frame.

This will be used by unwind user sframe, as SFrame may represent an
undefined return address as indication for an outermost frame.

Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---
 arch/x86/include/asm/unwind_user.h | 6 ++++--
 include/linux/unwind_user_types.h  | 1 +
 kernel/unwind/user.c               | 6 ++++++
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/unwind_user.h b/arch/x86/include/asm/unwind_user.h
index 6e469044e4de..2dfb5ef11e36 100644
--- a/arch/x86/include/asm/unwind_user.h
+++ b/arch/x86/include/asm/unwind_user.h
@@ -23,13 +23,15 @@ static inline int unwind_user_word_size(struct pt_regs *regs)
 	.cfa_off	=  2*(ws),			\
 	.ra_off		= -1*(ws),			\
 	.fp_off		= -2*(ws),			\
-	.use_fp		= true,
+	.use_fp		= true,				\
+	.outermost	= false,
 
 #define ARCH_INIT_USER_FP_ENTRY_FRAME(ws)		\
 	.cfa_off	=  1*(ws),			\
 	.ra_off		= -1*(ws),			\
 	.fp_off		= 0,				\
-	.use_fp		= false,
+	.use_fp		= false,			\
+	.outermost	= false,
 
 static inline bool unwind_user_at_function_start(struct pt_regs *regs)
 {
diff --git a/include/linux/unwind_user_types.h b/include/linux/unwind_user_types.h
index 43e4b160883f..616cc5ee4586 100644
--- a/include/linux/unwind_user_types.h
+++ b/include/linux/unwind_user_types.h
@@ -32,6 +32,7 @@ struct unwind_user_frame {
 	s32 ra_off;
 	s32 fp_off;
 	bool use_fp;
+	bool outermost;
 };
 
 struct unwind_user_state {
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index 1fb272419733..fdb1001e3750 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -32,6 +32,12 @@ static int unwind_user_next_common(struct unwind_user_state *state,
 {
 	unsigned long cfa, fp, ra;
 
+	/* Stop unwinding when reaching an outermost frame. */
+	if (frame->outermost) {
+		state->done = true;
+		return 0;
+	}
+
 	/* Get the Canonical Frame Address (CFA) */
 	if (frame->use_fp) {
 		if (state->fp < state->sp)
-- 
2.51.0

[PATCH v16 09/20] unwind_user/sframe: Add support for outermost frame indication

[Jens Remus]

SFrame may represent an undefined return address (RA) as SFrame FRE
without any offsets as indication for an outermost frame.

Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---
 kernel/unwind/sframe.c | 15 ++++++++++++++-
 kernel/unwind/sframe.h |  1 +
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 2de29c836f6b..41ece3ca62a1 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -231,7 +231,7 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	UNSAFE_GET_USER_INC(info, cur, 1, Efault);
 	dataword_count = SFRAME_V3_FRE_DATAWORD_COUNT(info);
 	dataword_size  = dataword_size_enum_to_size(SFRAME_V3_FRE_DATAWORD_SIZE(info));
-	if (!dataword_count || !dataword_size)
+	if (!dataword_size)
 		return -EINVAL;
 	fre_size = addr_size + 1 + (dataword_count * dataword_size);
 
@@ -242,6 +242,17 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	if (fde_type != SFRAME_FDE_TYPE_DEFAULT)
 		return -EINVAL;
 
+	if (!dataword_count) {
+		/*
+		 * A FRE without data words indicates RA undefined /
+		 * outermost frame.
+		 */
+		cfa_off	= 0;
+		ra_off	= 0;
+		fp_off	= 0;
+		goto done;
+	}
+
 	UNSAFE_GET_USER_INC(cfa_off, cur, dataword_size, Efault);
 	dataword_count--;
 
@@ -262,6 +273,7 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	if (dataword_count)
 		return -EINVAL;
 
+done:
 	fre->size	= fre_size;
 	fre->ip_off	= ip_off;
 	fre->cfa_off	= cfa_off;
@@ -328,6 +340,7 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 	frame->ra_off  = fre->ra_off;
 	frame->fp_off  = fre->fp_off;
 	frame->use_fp  = SFRAME_V3_FRE_CFA_BASE_REG_ID(fre->info) == SFRAME_BASE_REG_FP;
+	frame->outermost = SFRAME_V3_FRE_RA_UNDEFINED_P(fre->info);
 
 	return 0;
 }
diff --git a/kernel/unwind/sframe.h b/kernel/unwind/sframe.h
index fc2908e92c7b..ed111fd0d702 100644
--- a/kernel/unwind/sframe.h
+++ b/kernel/unwind/sframe.h
@@ -77,5 +77,6 @@ struct sframe_fda_v3 {
 #define SFRAME_V3_FRE_DATAWORD_COUNT(info)		(((info) >> 1) & 0xf)
 #define SFRAME_V3_FRE_DATAWORD_SIZE(info)		(((info) >> 5) & 0x3)
 #define SFRAME_V3_AARCH64_FRE_MANGLED_RA_P(info)	(((info) >> 7) & 0x1)
+#define SFRAME_V3_FRE_RA_UNDEFINED_P(info)		(SFRAME_V3_FRE_DATAWORD_COUNT(info) == 0)
 
 #endif /* _SFRAME_H */
-- 
2.51.0

[PATCH v16 10/20] unwind_user/sframe: Remove .sframe section on detected corruption

[Jens Remus]

From: Josh Poimboeuf <jpoimboe@kernel.org>

To avoid continued attempted use of a bad .sframe section, remove it
on demand when the first sign of corruption is detected.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v15:
    - sframe_find(): Align to normalized error code usage and remove .sframe
      for all but ENOENT.  Also remove if user_read_access_begin() fails.

 kernel/unwind/sframe.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 41ece3ca62a1..e0eb2adf5a07 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -371,10 +371,15 @@ int sframe_find(unsigned long ip, struct unwind_user_frame *frame)
 			ret = __find_fre(sec, &fde, ip, frame);
 	}
 
+end:
+	if (ret && ret != -ENOENT)
+		WARN_ON_ONCE(sframe_remove_section(sec->sframe_start));
+
 	return ret;
 
 Efault:
-	return -EFAULT;
+	ret = -EFAULT;
+	goto end;
 }
 
 static void free_section(struct sframe_section *sec)
-- 
2.51.0

[PATCH v16 11/20] unwind_user/sframe: Show file name in debug output

[Jens Remus]

From: Josh Poimboeuf <jpoimboe@kernel.org>

When debugging sframe issues, the error messages aren't all that helpful
without knowing what file a corresponding .sframe section belongs to.
Prefix debug output strings with the file name.

[ Jens Remus: Fix checkpatch error "space prohibited before that close
parenthesis ')'". ]

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v15:
    - Use GFP_KERNEL_ACCOUNT instead of GFP_KERNEL (see
      memory-allocation.rst, section "Get Free Page flags"). (Sashiko AI)
    
    Changes in v14:
    - Uppercase terms FDE and FRE in debug messages.

 include/linux/sframe.h       |  4 +++-
 kernel/unwind/sframe.c       | 23 ++++++++++--------
 kernel/unwind/sframe_debug.h | 45 +++++++++++++++++++++++++++++++-----
 3 files changed, 56 insertions(+), 16 deletions(-)

diff --git a/include/linux/sframe.h b/include/linux/sframe.h
index 9a72209696f9..b79c5ec09229 100644
--- a/include/linux/sframe.h
+++ b/include/linux/sframe.h
@@ -10,7 +10,9 @@
 
 struct sframe_section {
 	struct rcu_head	rcu;
-
+#ifdef CONFIG_DYNAMIC_DEBUG
+	const char	*filename;
+#endif
 	unsigned long	sframe_start;
 	unsigned long	sframe_end;
 	unsigned long	text_start;
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index e0eb2adf5a07..2cfa274cd8dc 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -372,8 +372,10 @@ int sframe_find(unsigned long ip, struct unwind_user_frame *frame)
 	}
 
 end:
-	if (ret && ret != -ENOENT)
+	if (ret && ret != -ENOENT) {
+		dbg_sec("removing bad .sframe section\n");
 		WARN_ON_ONCE(sframe_remove_section(sec->sframe_start));
+	}
 
 	return ret;
 
@@ -384,6 +386,7 @@ int sframe_find(unsigned long ip, struct unwind_user_frame *frame)
 
 static void free_section(struct sframe_section *sec)
 {
+	dbg_free(sec);
 	kfree(sec);
 }
 
@@ -403,7 +406,7 @@ static int sframe_read_header(struct sframe_section *sec)
 	BUILD_BUG_ON(!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS));
 
 	if (copy_from_user(&shdr, (void __user *)sec->sframe_start, sizeof(shdr))) {
-		dbg("header usercopy failed\n");
+		dbg_sec("header usercopy failed\n");
 		return -EFAULT;
 	}
 
@@ -412,18 +415,18 @@ static int sframe_read_header(struct sframe_section *sec)
 	    !(shdr.preamble.flags & SFRAME_F_FDE_SORTED) ||
 	    !(shdr.preamble.flags & SFRAME_F_FDE_FUNC_START_PCREL) ||
 	    shdr.auxhdr_len) {
-		dbg("bad/unsupported sframe header\n");
+		dbg_sec("bad/unsupported sframe header\n");
 		return -EINVAL;
 	}
 
 	if (!shdr.num_fdes || !shdr.num_fres) {
-		dbg("no fde/fre entries\n");
+		dbg_sec("no FDE/FRE entries\n");
 		return -EINVAL;
 	}
 
 	header_end = sec->sframe_start + SFRAME_HEADER_SIZE(shdr);
 	if (header_end >= sec->sframe_end) {
-		dbg("header doesn't fit in section\n");
+		dbg_sec("header doesn't fit in section\n");
 		return -EINVAL;
 	}
 
@@ -435,7 +438,7 @@ static int sframe_read_header(struct sframe_section *sec)
 	fres_end   = fres_start + shdr.fre_len;
 
 	if (fres_start < fdes_end || fres_end > sec->sframe_end) {
-		dbg("inconsistent fde/fre offsets\n");
+		dbg_sec("inconsistent FDE/FRE offsets\n");
 		return -EINVAL;
 	}
 
@@ -491,6 +494,8 @@ int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
 	sec->text_start		= text_start;
 	sec->text_end		= text_end;
 
+	dbg_init(sec);
+
 	ret = sframe_read_header(sec);
 	if (ret) {
 		dbg_print_header(sec);
@@ -500,8 +505,8 @@ int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
 	ret = mtree_insert_range(sframe_mt, sec->text_start, sec->text_end - 1,
 				 sec, GFP_KERNEL_ACCOUNT);
 	if (ret) {
-		dbg("mtree_insert_range failed: text=%lx-%lx\n",
-		    sec->text_start, sec->text_end);
+		dbg_sec("mtree_insert_range failed: text=%lx-%lx\n",
+			sec->text_start, sec->text_end);
 		goto err_free;
 	}
 
@@ -523,7 +528,7 @@ static int __sframe_remove_section(struct mm_struct *mm,
 				   struct sframe_section *sec)
 {
 	if (!mtree_erase(&mm->sframe_mt, sec->text_start)) {
-		dbg("mtree_erase failed: text=%lx\n", sec->text_start);
+		dbg_sec("mtree_erase failed: text=%lx\n", sec->text_start);
 		return -EINVAL;
 	}
 
diff --git a/kernel/unwind/sframe_debug.h b/kernel/unwind/sframe_debug.h
index 36352124cde8..a63e75cccc70 100644
--- a/kernel/unwind/sframe_debug.h
+++ b/kernel/unwind/sframe_debug.h
@@ -10,26 +10,59 @@
 #define dbg(fmt, ...)							\
 	pr_debug("%s (%d): " fmt, current->comm, current->pid, ##__VA_ARGS__)
 
+#define dbg_sec(fmt, ...)						\
+	dbg("%s: " fmt, sec->filename, ##__VA_ARGS__)
+
 static __always_inline void dbg_print_header(struct sframe_section *sec)
 {
 	unsigned long fdes_end;
 
 	fdes_end = sec->fdes_start + (sec->num_fdes * sizeof(struct sframe_fde_v3));
 
-	dbg("SEC: sframe:0x%lx-0x%lx text:0x%lx-0x%lx "
-	    "fdes:0x%lx-0x%lx fres:0x%lx-0x%lx "
-	    "ra_off:%d fp_off:%d\n",
-	    sec->sframe_start, sec->sframe_end, sec->text_start, sec->text_end,
-	    sec->fdes_start, fdes_end, sec->fres_start, sec->fres_end,
-	    sec->ra_off, sec->fp_off);
+	dbg_sec("SEC: sframe:0x%lx-0x%lx text:0x%lx-0x%lx "
+		"fdes:0x%lx-0x%lx fres:0x%lx-0x%lx "
+		"ra_off:%d fp_off:%d\n",
+		sec->sframe_start, sec->sframe_end, sec->text_start, sec->text_end,
+		sec->fdes_start, fdes_end, sec->fres_start, sec->fres_end,
+		sec->ra_off, sec->fp_off);
+}
+
+static inline void dbg_init(struct sframe_section *sec)
+{
+	struct mm_struct *mm = current->mm;
+	struct vm_area_struct *vma;
+
+	guard(mmap_read_lock)(mm);
+	vma = vma_lookup(mm, sec->sframe_start);
+	if (!vma)
+		sec->filename = kstrdup("(vma gone???)", GFP_KERNEL_ACCOUNT);
+	else if (vma->vm_file)
+		sec->filename = kstrdup_quotable_file(vma->vm_file, GFP_KERNEL_ACCOUNT);
+	else if (vma->vm_ops && vma->vm_ops->name)
+		sec->filename = kstrdup(vma->vm_ops->name(vma), GFP_KERNEL_ACCOUNT);
+	else if (arch_vma_name(vma))
+		sec->filename = kstrdup(arch_vma_name(vma), GFP_KERNEL_ACCOUNT);
+	else if (!vma->vm_mm)
+		sec->filename = kstrdup("(vdso)", GFP_KERNEL_ACCOUNT);
+	else
+		sec->filename = kstrdup("(anonymous)", GFP_KERNEL_ACCOUNT);
+}
+
+static inline void dbg_free(struct sframe_section *sec)
+{
+	kfree(sec->filename);
 }
 
 #else /* !CONFIG_DYNAMIC_DEBUG */
 
 #define dbg(args...)			no_printk(args)
+#define dbg_sec(args...)		no_printk(args)
 
 static inline void dbg_print_header(struct sframe_section *sec) {}
 
+static inline void dbg_init(struct sframe_section *sec) {}
+static inline void dbg_free(struct sframe_section *sec) {}
+
 #endif /* !CONFIG_DYNAMIC_DEBUG */
 
 #endif /* _SFRAME_DEBUG_H */
-- 
2.51.0

[PATCH v16 12/20] unwind_user/sframe: Add .sframe validation option

[Jens Remus]

From: Josh Poimboeuf <jpoimboe@kernel.org>

Add a debug feature to validate all .sframe sections when first loading
the file rather than on demand.

[ Jens Remus: Add support for SFrame V3.  Add support for PC-relative
FDE function start offset.  Adjust to rename of struct sframe_fre to
sframe_fre_internal.  Use %#x/%#lx format specifiers. ]

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v16:
    - sframe_validate_section(): Allow for a FDE[0] function start address
      of zero. (Sashiko AI)
    - sframe_validate_section(): Replace alternation between two FREs with
      simpler logic used for FDE and use a prev_ip_off.
    
    Changes in v15:
    - sframe_validate_section(): Fix format specifier for number of FREs
      in debug message. (Sashiko AI)
    - Normalize error code usage (.sframe is removed for all but ENOENT):
      ENOENT: No sframe or no FDE for IP found
              (FDE found but no FRE is EINVAL)
      EFAULT: Bad address
      EINVAL: Invalid input or sframe
    
    Changes in v14:
    - Add debug message if safe_read_fde() fails.
    - Update function names in debug messages.
    - Uppercase terms FDE and FRE in debug messages.
    
    Changes in v13:
    - Update to SFrame V3:
      - Print struct sframe_fde_internal fields fda_off and info2 in debug
        message.
    - Adjust to rename of struct sframe_fde_internal field func_start_addr
      to func_addr.
    - Use format strings "%#x" and "%#lx" instead of "0x%x" and "0x%lx".
    - Reword commit message (my changes).

 arch/Kconfig           | 19 +++++++++
 kernel/unwind/sframe.c | 92 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 111 insertions(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index 37549832bd1f..132249d342a3 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -490,6 +490,25 @@ config HAVE_UNWIND_USER_SFRAME
 	bool
 	select UNWIND_USER
 
+config SFRAME_VALIDATION
+	bool "Enable .sframe section debugging"
+	depends on HAVE_UNWIND_USER_SFRAME
+	depends on DYNAMIC_DEBUG
+	help
+	  When adding an .sframe section for a task, validate the entire
+	  section immediately rather than on demand.
+
+	  This is a debug feature which is helpful for rooting out .sframe
+	  section issues.  If the .sframe section is corrupt, it will fail to
+	  load immediately, with more information provided in dynamic printks.
+
+	  This has a significant page cache footprint due to its reading of the
+	  entire .sframe section for every loaded executable and shared
+	  library.  Also, it's done for all processes, even those which don't
+	  get stack traced by the kernel.  Not recommended for general use.
+
+	  If unsure, say N.
+
 config HAVE_PERF_REGS
 	bool
 	help
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 2cfa274cd8dc..e6d66ae8e7ac 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -384,6 +384,94 @@ int sframe_find(unsigned long ip, struct unwind_user_frame *frame)
 	goto end;
 }
 
+#ifdef CONFIG_SFRAME_VALIDATION
+
+static int safe_read_fde(struct sframe_section *sec,
+			 unsigned int fde_num, struct sframe_fde_internal *fde)
+{
+	int ret;
+
+	if (!user_read_access_begin((void __user *)sec->sframe_start,
+				    sec->sframe_end - sec->sframe_start))
+		return -EFAULT;
+	ret = __read_fde(sec, fde_num, fde);
+	user_read_access_end();
+	return ret;
+}
+
+static int safe_read_fre(struct sframe_section *sec,
+			 struct sframe_fde_internal *fde,
+			 unsigned long fre_addr,
+			 struct sframe_fre_internal *fre)
+{
+	int ret;
+
+	if (!user_read_access_begin((void __user *)sec->sframe_start,
+				    sec->sframe_end - sec->sframe_start))
+		return -EFAULT;
+	ret = __read_fre(sec, fde, fre_addr, fre);
+	user_read_access_end();
+	return ret;
+}
+
+static int sframe_validate_section(struct sframe_section *sec)
+{
+	struct sframe_fde_internal fde;
+	unsigned long prev_func_addr;
+	unsigned int i;
+
+	for (i = 0; i < sec->num_fdes; i++) {
+		struct sframe_fre_internal fre;
+		unsigned long fre_addr;
+		u32 prev_ip_off;
+		unsigned int j;
+		int ret;
+
+		ret = safe_read_fde(sec, i, &fde);
+		if (ret) {
+			dbg_sec("safe_read_fde(%u) failed\n", i);
+			return ret;
+		}
+
+		if (i && fde.func_addr <= prev_func_addr) {
+			dbg_sec("FDE %u not sorted\n", i);
+			return -EINVAL;
+		}
+		prev_func_addr = fde.func_addr;
+
+		fre_addr = sec->fres_start + fde.fres_off;
+		for (j = 0; j < fde.fres_num; j++) {
+			ret = safe_read_fre(sec, &fde, fre_addr, &fre);
+			if (ret) {
+				dbg_sec("FDE %u: safe_read_fre(%u) failed\n", i, j);
+				dbg_sec("FDE: func_addr:%#lx func_size:%#x fda_off:%#x fres_off:%#x fres_num:%u info:%u info2:%u rep_size:%u\n",
+					fde.func_addr, fde.func_size,
+					fde.fda_off,
+					fde.fres_off, fde.fres_num,
+					fde.info, fde.info2,
+					fde.rep_size);
+				return ret;
+			}
+
+			if (j && fre.ip_off <= prev_ip_off) {
+				dbg_sec("FDE %u: FRE %u not sorted\n", i, j);
+				return -EINVAL;
+			}
+			prev_ip_off = fre.ip_off;
+
+			fre_addr += fre.size;
+		}
+	}
+
+	return 0;
+}
+
+#else /*  !CONFIG_SFRAME_VALIDATION */
+
+static int sframe_validate_section(struct sframe_section *sec) { return 0; }
+
+#endif /* !CONFIG_SFRAME_VALIDATION */
+
 static void free_section(struct sframe_section *sec)
 {
 	dbg_free(sec);
@@ -502,6 +590,10 @@ int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
 		goto err_free;
 	}
 
+	ret = sframe_validate_section(sec);
+	if (ret)
+		goto err_free;
+
 	ret = mtree_insert_range(sframe_mt, sec->text_start, sec->text_end - 1,
 				 sec, GFP_KERNEL_ACCOUNT);
 	if (ret) {
-- 
2.51.0

[PATCH v16 13/20] unwind_user: Enable archs that pass RA in a register

[Jens Remus]

Not all architectures/ABIs pass the return address (RA) on the stack on
function entry, like x86-64 does due to its CALL instruction pushing
the RA onto the stack.  Architectures/ABIs, such as s390, also do not
require the RA to be saved on the stack in the function prologue.  In
particular, the RA may never be saved to the stack at all, such as in
leaf functions.  Unwinding must therefore not assume the presence of a
RA saved on stack for the topmost frame.

Treat a RA offset from CFA of zero as indication that the RA is not
saved (on the stack).  For the topmost frame treat it as indication that
the RA is in the link/RA register, such as on arm64 and s390, and obtain
it from there.  For non-topmost frames treat it as error, as the RA must
be saved.

Additionally allow the SP to be unchanged in the topmost frame, for
architectures where SP at function entry == SP at call site, such as
arm64 and s390.

Note that treating a RA offset from CFA of zero as indication that
the RA is not saved on the stack additionally allows for architectures,
such as s390, where the frame pointer (FP) may be saved without the RA
being saved as well.  Provided that such architectures represent this
in SFrame by encoding the "missing" RA offset using a padding RA offset
with a value of zero.

Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v15:
    - Define pr_fmt().
    - unwind_user_get_ra_reg(): Use pr_debug_once() instead of
      WARN_ON_ONCE() to prevent user-triggered warning/panic. (Sashiko AI)
    - Reworded commit message. (Indu)

 include/linux/unwind_user.h | 10 ++++++++++
 kernel/unwind/sframe.c      |  6 ++----
 kernel/unwind/user.c        | 20 ++++++++++++++++----
 3 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/include/linux/unwind_user.h b/include/linux/unwind_user.h
index 64618618febd..7bf58f23aa64 100644
--- a/include/linux/unwind_user.h
+++ b/include/linux/unwind_user.h
@@ -23,6 +23,16 @@ static inline bool unwind_user_at_function_start(struct pt_regs *regs)
 #define unwind_user_at_function_start unwind_user_at_function_start
 #endif
 
+#ifndef unwind_user_get_ra_reg
+static inline int unwind_user_get_ra_reg(unsigned long *val)
+{
+	pr_debug_once("%s (%d): unwind_user_get_ra_reg() not implemented\n",
+		      current->comm, current->pid);
+	return -EINVAL;
+}
+#define unwind_user_get_ra_reg unwind_user_get_ra_reg
+#endif
+
 int unwind_user(struct unwind_stacktrace *trace, unsigned int max_entries);
 
 #endif /* _LINUX_UNWIND_USER_H */
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index e6d66ae8e7ac..d573c2529926 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -257,10 +257,8 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	dataword_count--;
 
 	ra_off = sec->ra_off;
-	if (!ra_off) {
-		if (!dataword_count--)
-			return -EINVAL;
-
+	if (!ra_off && dataword_count) {
+		dataword_count--;
 		UNSAFE_GET_USER_INC(ra_off, cur, dataword_size, Efault);
 	}
 
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index fdb1001e3750..afa7c6f6d9b4 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -2,6 +2,9 @@
 /*
 * Generic interfaces for unwinding user space
 */
+
+#define pr_fmt(fmt)	"unwind_user: " fmt
+
 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/sched/task_stack.h>
@@ -48,8 +51,12 @@ static int unwind_user_next_common(struct unwind_user_state *state,
 	}
 	cfa += frame->cfa_off;
 
-	/* Make sure that stack is not going in wrong direction */
-	if (cfa <= state->sp)
+	/*
+	 * Make sure that stack is not going in wrong direction.  Allow SP
+	 * to be unchanged for the topmost frame, by subtracting topmost,
+	 * which is either 0 or 1.
+	 */
+	if (cfa <= state->sp - state->topmost)
 		return -EINVAL;
 
 	/* Make sure that the address is word aligned */
@@ -57,8 +64,13 @@ static int unwind_user_next_common(struct unwind_user_state *state,
 		return -EINVAL;
 
 	/* Get the Return Address (RA) */
-	if (get_user_word(&ra, cfa, frame->ra_off, state->ws))
-		return -EINVAL;
+	if (frame->ra_off) {
+		if (get_user_word(&ra, cfa, frame->ra_off, state->ws))
+			return -EINVAL;
+	} else {
+		if (!state->topmost || unwind_user_get_ra_reg(&ra))
+			return -EINVAL;
+	}
 
 	/* Get the Frame Pointer (FP) */
 	if (frame->fp_off && get_user_word(&fp, cfa, frame->fp_off, state->ws))
-- 
2.51.0

[PATCH v16 14/20] unwind_user: Flexible FP/RA recovery rules

[Jens Remus]

To enable support for SFrame V3 flexible FDEs with a subsequent patch,
add support for the following flexible frame pointer (FP) and return
address (RA) recovery rules:

  FP/RA = *(CFA + offset)
  FP/RA = register + offset
  FP/RA = *(register + offset)

Note that FP/RA recovery rules that use arbitrary register contents are
only valid when in the topmost frame, as their contents are otherwise
unknown.

This also enables unwinding of user space for architectures, such as
s390, that may save the frame pointer (FP) and/or return address (RA) in
other registers, for instance when in a leaf function.

Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v15:
    - Define dbg_once().
    - unwind_user_get_reg(): Use pr_debug_once() instead of WARN_ON_ONCE()
      to prevent user-triggered warning/panic. (Sashiko AI)
    - unwind_user_next_common(): Handle UNWIND_USER_RULE_CFA_OFFSET for RA
      and FP to use dbg_once() instead of WARN_ON_ONCE() to prevent user-
      triggered warning/panic. (Sashiko AI)
    
    Changes in v14:
    - Improve comment on why UNWIND_USER_RULE_CFA_OFFSET is not implemented.
      (Mark Rutland)

 arch/x86/include/asm/unwind_user.h | 21 +++++++--
 include/linux/unwind_user.h        | 10 +++++
 include/linux/unwind_user_types.h  | 23 +++++++++-
 kernel/unwind/sframe.c             | 16 ++++++-
 kernel/unwind/user.c               | 70 +++++++++++++++++++++++++++---
 5 files changed, 125 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/unwind_user.h b/arch/x86/include/asm/unwind_user.h
index 2dfb5ef11e36..9c3417be4283 100644
--- a/arch/x86/include/asm/unwind_user.h
+++ b/arch/x86/include/asm/unwind_user.h
@@ -21,15 +21,26 @@ static inline int unwind_user_word_size(struct pt_regs *regs)
 
 #define ARCH_INIT_USER_FP_FRAME(ws)			\
 	.cfa_off	=  2*(ws),			\
-	.ra_off		= -1*(ws),			\
-	.fp_off		= -2*(ws),			\
+	.ra		= {				\
+		.rule		= UNWIND_USER_RULE_CFA_OFFSET_DEREF,\
+		.offset		= -1*(ws),		\
+			},				\
+	.fp		= {				\
+		.rule		= UNWIND_USER_RULE_CFA_OFFSET_DEREF,\
+		.offset		= -2*(ws),		\
+			},				\
 	.use_fp		= true,				\
 	.outermost	= false,
 
 #define ARCH_INIT_USER_FP_ENTRY_FRAME(ws)		\
 	.cfa_off	=  1*(ws),			\
-	.ra_off		= -1*(ws),			\
-	.fp_off		= 0,				\
+	.ra		= {				\
+		.rule		= UNWIND_USER_RULE_CFA_OFFSET_DEREF,\
+		.offset		= -1*(ws),		\
+			},				\
+	.fp		= {				\
+		.rule		= UNWIND_USER_RULE_RETAIN,\
+			},				\
 	.use_fp		= false,			\
 	.outermost	= false,
 
@@ -41,4 +52,6 @@ static inline bool unwind_user_at_function_start(struct pt_regs *regs)
 
 #endif /* CONFIG_HAVE_UNWIND_USER_FP */
 
+#include <asm-generic/unwind_user.h>
+
 #endif /* _ASM_X86_UNWIND_USER_H */
diff --git a/include/linux/unwind_user.h b/include/linux/unwind_user.h
index 7bf58f23aa64..6aca38f89ddd 100644
--- a/include/linux/unwind_user.h
+++ b/include/linux/unwind_user.h
@@ -33,6 +33,16 @@ static inline int unwind_user_get_ra_reg(unsigned long *val)
 #define unwind_user_get_ra_reg unwind_user_get_ra_reg
 #endif
 
+#ifndef unwind_user_get_reg
+static inline int unwind_user_get_reg(unsigned long *val, unsigned int regnum)
+{
+	pr_debug_once("%s (%d): unwind_user_get_reg(%u) not implemented\n",
+		      current->comm, current->pid, regnum);
+	return -EINVAL;
+}
+#define unwind_user_get_reg unwind_user_get_reg
+#endif
+
 int unwind_user(struct unwind_stacktrace *trace, unsigned int max_entries);
 
 #endif /* _LINUX_UNWIND_USER_H */
diff --git a/include/linux/unwind_user_types.h b/include/linux/unwind_user_types.h
index 616cc5ee4586..0d02714a1b5d 100644
--- a/include/linux/unwind_user_types.h
+++ b/include/linux/unwind_user_types.h
@@ -27,10 +27,29 @@ struct unwind_stacktrace {
 	unsigned long	*entries;
 };
 
+#define UNWIND_USER_RULE_DEREF			BIT(31)
+
+enum unwind_user_rule {
+	UNWIND_USER_RULE_RETAIN,		/* entity = entity */
+	UNWIND_USER_RULE_CFA_OFFSET,		/* entity = CFA + offset */
+	UNWIND_USER_RULE_REG_OFFSET,		/* entity = register + offset */
+	/* DEREF variants */
+	UNWIND_USER_RULE_CFA_OFFSET_DEREF =	/* entity = *(CFA + offset) */
+		UNWIND_USER_RULE_CFA_OFFSET | UNWIND_USER_RULE_DEREF,
+	UNWIND_USER_RULE_REG_OFFSET_DEREF =	/* entity = *(register + offset) */
+		UNWIND_USER_RULE_REG_OFFSET | UNWIND_USER_RULE_DEREF,
+};
+
+struct unwind_user_rule_data {
+	enum unwind_user_rule rule;
+	s32 offset;
+	unsigned int regnum;
+};
+
 struct unwind_user_frame {
 	s32 cfa_off;
-	s32 ra_off;
-	s32 fp_off;
+	struct unwind_user_rule_data ra;
+	struct unwind_user_rule_data fp;
 	bool use_fp;
 	bool outermost;
 };
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index d573c2529926..29a874a67f32 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -285,6 +285,18 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	return -EFAULT;
 }
 
+static __always_inline void
+sframe_init_rule_data(struct unwind_user_rule_data *rule_data,
+		      s32 offset)
+{
+	if (offset) {
+		rule_data->rule = UNWIND_USER_RULE_CFA_OFFSET_DEREF;
+		rule_data->offset = offset;
+	} else {
+		rule_data->rule = UNWIND_USER_RULE_RETAIN;
+	}
+}
+
 static __always_inline int __find_fre(struct sframe_section *sec,
 				      struct sframe_fde_internal *fde,
 				      unsigned long ip,
@@ -335,8 +347,8 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 	fre = prev_fre;
 
 	frame->cfa_off = fre->cfa_off;
-	frame->ra_off  = fre->ra_off;
-	frame->fp_off  = fre->fp_off;
+	sframe_init_rule_data(&frame->ra, fre->ra_off);
+	sframe_init_rule_data(&frame->fp, fre->fp_off);
 	frame->use_fp  = SFRAME_V3_FRE_CFA_BASE_REG_ID(fre->info) == SFRAME_BASE_REG_FP;
 	frame->outermost = SFRAME_V3_FRE_RA_UNDEFINED_P(fre->info);
 
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index afa7c6f6d9b4..c6a2abac78e0 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -12,6 +12,17 @@
 #include <linux/uaccess.h>
 #include <linux/sframe.h>
 
+#ifdef CONFIG_DYNAMIC_DEBUG
+
+#define dbg_once(fmt, ...)							\
+	pr_debug_once("%s (%d): " fmt, current->comm, current->pid, ##__VA_ARGS__)
+
+#else /* !CONFIG_DYNAMIC_DEBUG */
+
+#define dbg_once(args...)		no_printk(args)
+
+#endif /* !CONFIG_DYNAMIC_DEBUG */
+
 #define for_each_user_frame(state) \
 	for (unwind_user_start(state); !(state)->done; unwind_user_next(state))
 
@@ -64,22 +75,67 @@ static int unwind_user_next_common(struct unwind_user_state *state,
 		return -EINVAL;
 
 	/* Get the Return Address (RA) */
-	if (frame->ra_off) {
-		if (get_user_word(&ra, cfa, frame->ra_off, state->ws))
-			return -EINVAL;
-	} else {
+	switch (frame->ra.rule) {
+	case UNWIND_USER_RULE_RETAIN:
 		if (!state->topmost || unwind_user_get_ra_reg(&ra))
 			return -EINVAL;
+		break;
+	case UNWIND_USER_RULE_CFA_OFFSET:
+		/*
+		 * RA = CFA + offset does not make sense.
+		 * A return address cannot legitimately be a stack address.
+		 */
+		dbg_once("UNWIND_USER_RULE_CFA_OFFSET invalid for RA\n");
+		return -EINVAL;
+	case UNWIND_USER_RULE_CFA_OFFSET_DEREF:
+		ra = cfa + frame->ra.offset;
+		break;
+	case UNWIND_USER_RULE_REG_OFFSET:
+	case UNWIND_USER_RULE_REG_OFFSET_DEREF:
+		if (!state->topmost || unwind_user_get_reg(&ra, frame->ra.regnum))
+			return -EINVAL;
+		ra += frame->ra.offset;
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		return -EINVAL;
 	}
+	if (frame->ra.rule & UNWIND_USER_RULE_DEREF &&
+	    get_user_word(&ra, ra, 0, state->ws))
+		return -EINVAL;
 
 	/* Get the Frame Pointer (FP) */
-	if (frame->fp_off && get_user_word(&fp, cfa, frame->fp_off, state->ws))
+	switch (frame->fp.rule) {
+	case UNWIND_USER_RULE_RETAIN:
+		fp = state->fp;
+		break;
+	case UNWIND_USER_RULE_CFA_OFFSET:
+		/*
+		 * FP = CFA + offset is currently not used for FP
+		 * (e.g. SFrame cannot represent this rule).
+		 */
+		dbg_once("UNWIND_USER_RULE_CFA_OFFSET unsupported for FP\n");
+		return -EINVAL;
+	case UNWIND_USER_RULE_CFA_OFFSET_DEREF:
+		fp = cfa + frame->fp.offset;
+		break;
+	case UNWIND_USER_RULE_REG_OFFSET:
+	case UNWIND_USER_RULE_REG_OFFSET_DEREF:
+		if (!state->topmost || unwind_user_get_reg(&fp, frame->fp.regnum))
+			return -EINVAL;
+		fp += frame->fp.offset;
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		return -EINVAL;
+	}
+	if (frame->fp.rule & UNWIND_USER_RULE_DEREF &&
+	    get_user_word(&fp, fp, 0, state->ws))
 		return -EINVAL;
 
 	state->ip = ra;
 	state->sp = cfa;
-	if (frame->fp_off)
-		state->fp = fp;
+	state->fp = fp;
 	state->topmost = false;
 	return 0;
 }
-- 
2.51.0

[PATCH v16 15/20] unwind_user: Flexible CFA recovery rules

[Jens Remus]

To enable support for SFrame V3 flexible FDEs with a subsequent patch,
add support for the following flexible Canonical Frame Address (CFA)
recovery rules:

  CFA = SP + offset
  CFA = *(SP + offset)
  CFA = FP + offset
  CFA = *(FP + offset)
  CFA = register + offset
  CFA = *(register + offset)

Note that CFA recovery rules that use arbitrary register contents are
only valid when in the topmost frame, as their contents are otherwise
unknown.

Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v15:
    - enum unwind_user_cfa_rule, unwind_user_next_common(): Add support for
      SP/FP-based CFA recovery rules with dereferencing. (Sashiko AI)

 arch/x86/include/asm/unwind_user.h | 12 ++++++++----
 include/linux/unwind_user_types.h  | 22 ++++++++++++++++++++--
 kernel/unwind/sframe.c             | 15 +++++++++++++--
 kernel/unwind/user.c               | 24 ++++++++++++++++++++----
 4 files changed, 61 insertions(+), 12 deletions(-)

diff --git a/arch/x86/include/asm/unwind_user.h b/arch/x86/include/asm/unwind_user.h
index 9c3417be4283..f38f7c5ff1de 100644
--- a/arch/x86/include/asm/unwind_user.h
+++ b/arch/x86/include/asm/unwind_user.h
@@ -20,7 +20,10 @@ static inline int unwind_user_word_size(struct pt_regs *regs)
 #ifdef CONFIG_HAVE_UNWIND_USER_FP
 
 #define ARCH_INIT_USER_FP_FRAME(ws)			\
-	.cfa_off	=  2*(ws),			\
+	.cfa		= {				\
+		.rule		= UNWIND_USER_CFA_RULE_FP_OFFSET,\
+		.offset		=  2*(ws),		\
+			},				\
 	.ra		= {				\
 		.rule		= UNWIND_USER_RULE_CFA_OFFSET_DEREF,\
 		.offset		= -1*(ws),		\
@@ -29,11 +32,13 @@ static inline int unwind_user_word_size(struct pt_regs *regs)
 		.rule		= UNWIND_USER_RULE_CFA_OFFSET_DEREF,\
 		.offset		= -2*(ws),		\
 			},				\
-	.use_fp		= true,				\
 	.outermost	= false,
 
 #define ARCH_INIT_USER_FP_ENTRY_FRAME(ws)		\
-	.cfa_off	=  1*(ws),			\
+	.cfa		= {				\
+		.rule		= UNWIND_USER_CFA_RULE_SP_OFFSET,\
+		.offset		=  1*(ws),		\
+			},				\
 	.ra		= {				\
 		.rule		= UNWIND_USER_RULE_CFA_OFFSET_DEREF,\
 		.offset		= -1*(ws),		\
@@ -41,7 +46,6 @@ static inline int unwind_user_word_size(struct pt_regs *regs)
 	.fp		= {				\
 		.rule		= UNWIND_USER_RULE_RETAIN,\
 			},				\
-	.use_fp		= false,			\
 	.outermost	= false,
 
 static inline bool unwind_user_at_function_start(struct pt_regs *regs)
diff --git a/include/linux/unwind_user_types.h b/include/linux/unwind_user_types.h
index 0d02714a1b5d..c18be5b7d586 100644
--- a/include/linux/unwind_user_types.h
+++ b/include/linux/unwind_user_types.h
@@ -29,6 +29,25 @@ struct unwind_stacktrace {
 
 #define UNWIND_USER_RULE_DEREF			BIT(31)
 
+enum unwind_user_cfa_rule {
+	UNWIND_USER_CFA_RULE_SP_OFFSET,		/* CFA = SP + offset */
+	UNWIND_USER_CFA_RULE_FP_OFFSET,		/* CFA = FP + offset */
+	UNWIND_USER_CFA_RULE_REG_OFFSET,	/* CFA = register + offset */
+	/* DEREF variants */
+	UNWIND_USER_CFA_RULE_SP_OFFSET_DEREF =	/* CFA = *(SP + offset) */
+		UNWIND_USER_CFA_RULE_SP_OFFSET | UNWIND_USER_RULE_DEREF,
+	UNWIND_USER_CFA_RULE_FP_OFFSET_DEREF =	/* CFA = *(FP + offset) */
+		UNWIND_USER_CFA_RULE_FP_OFFSET | UNWIND_USER_RULE_DEREF,
+	UNWIND_USER_CFA_RULE_REG_OFFSET_DEREF =	/* CFA = *(register + offset) */
+		UNWIND_USER_CFA_RULE_REG_OFFSET | UNWIND_USER_RULE_DEREF,
+};
+
+struct unwind_user_cfa_rule_data {
+	enum unwind_user_cfa_rule rule;
+	s32 offset;
+	unsigned int regnum;
+};
+
 enum unwind_user_rule {
 	UNWIND_USER_RULE_RETAIN,		/* entity = entity */
 	UNWIND_USER_RULE_CFA_OFFSET,		/* entity = CFA + offset */
@@ -47,10 +66,9 @@ struct unwind_user_rule_data {
 };
 
 struct unwind_user_frame {
-	s32 cfa_off;
+	struct unwind_user_cfa_rule_data cfa;
 	struct unwind_user_rule_data ra;
 	struct unwind_user_rule_data fp;
-	bool use_fp;
 	bool outermost;
 };
 
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 29a874a67f32..daa97d8b0231 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -285,6 +285,18 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	return -EFAULT;
 }
 
+static __always_inline void
+sframe_init_cfa_rule_data(struct unwind_user_cfa_rule_data *cfa_rule_data,
+			  unsigned char fre_info,
+			  s32 offset)
+{
+	if (SFRAME_V3_FRE_CFA_BASE_REG_ID(fre_info) == SFRAME_BASE_REG_FP)
+		cfa_rule_data->rule = UNWIND_USER_CFA_RULE_FP_OFFSET;
+	else
+		cfa_rule_data->rule = UNWIND_USER_CFA_RULE_SP_OFFSET;
+	cfa_rule_data->offset = offset;
+}
+
 static __always_inline void
 sframe_init_rule_data(struct unwind_user_rule_data *rule_data,
 		      s32 offset)
@@ -346,10 +358,9 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 		return -EINVAL;
 	fre = prev_fre;
 
-	frame->cfa_off = fre->cfa_off;
+	sframe_init_cfa_rule_data(&frame->cfa, fre->info, fre->cfa_off);
 	sframe_init_rule_data(&frame->ra, fre->ra_off);
 	sframe_init_rule_data(&frame->fp, fre->fp_off);
-	frame->use_fp  = SFRAME_V3_FRE_CFA_BASE_REG_ID(fre->info) == SFRAME_BASE_REG_FP;
 	frame->outermost = SFRAME_V3_FRE_RA_UNDEFINED_P(fre->info);
 
 	return 0;
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index c6a2abac78e0..447061b10613 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -53,14 +53,30 @@ static int unwind_user_next_common(struct unwind_user_state *state,
 	}
 
 	/* Get the Canonical Frame Address (CFA) */
-	if (frame->use_fp) {
+	switch (frame->cfa.rule) {
+	case UNWIND_USER_CFA_RULE_SP_OFFSET:
+	case UNWIND_USER_CFA_RULE_SP_OFFSET_DEREF:
+		cfa = state->sp;
+		break;
+	case UNWIND_USER_CFA_RULE_FP_OFFSET:
+	case UNWIND_USER_CFA_RULE_FP_OFFSET_DEREF:
 		if (state->fp < state->sp)
 			return -EINVAL;
 		cfa = state->fp;
-	} else {
-		cfa = state->sp;
+		break;
+	case UNWIND_USER_CFA_RULE_REG_OFFSET:
+	case UNWIND_USER_CFA_RULE_REG_OFFSET_DEREF:
+		if (!state->topmost || unwind_user_get_reg(&cfa, frame->cfa.regnum))
+			return -EINVAL;
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		return -EINVAL;
 	}
-	cfa += frame->cfa_off;
+	cfa += frame->cfa.offset;
+	if (frame->cfa.rule & UNWIND_USER_RULE_DEREF &&
+	    get_user_word(&cfa, cfa, 0, state->ws))
+		return -EINVAL;
 
 	/*
 	 * Make sure that stack is not going in wrong direction.  Allow SP
-- 
2.51.0

[PATCH v16 16/20] unwind_user/sframe: Add support for SFrame V3 flexible FDEs

[Jens Remus]

SFrame V3 introduces flexible FDEs in addition to the regular FDEs.
The key difference is that flexible FDEs encode the CFA, RA, and FP
tracking information using two FRE data words, a control word and an
offset, or a single padding data word of zero (e.g. to represent FP
without RA tracking information).

The control word contains the following information:
- reg_p: Whether to use the register contents (reg_p=1) specified
  by regnum or the CFA (reg_p=0) as base.
- deref_p: Whether to dereference.
- regnum: A DWARF register number.

The offset is added to the base (i.e. CFA or register contents).  Then
the resulting address may optionally be dereferenced.

This enables the following flexible CFA and FP/RA recovery rules:
- CFA = register + offset	// reg_p=1, deref_p=0
- CFA = *(register + offset)	// reg_p=1, deref_p=1
- FP/RA = *(CFA + offset)	// reg_p=0, deref_p=0
- FP/RA = register + offset	// reg_p=1, deref_p=0
- FP/RA = *(register + offset)	// reg_p=1, deref_p=1

Note that for the CFA a rule with reg_p=0 is invalid, as the value of
the CFA cannot be described using itself as base.  For FP/RA a rule with
reg_p=0 and deref_p=0 and regnum=0 is invalid, as it that is equal to
the padding data word of zero.

Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v16:
    - __find_fre(): Move declaration of ret to function scope to resolve
      compile error. (Sashiko AI)
    
    Changes in v15:
    - __read_flex_fde_fre_datawords(): Add comment on FRE dataword RA/FP
      location info decoding logic. (Sashiko AI)
    - Fix outermost frame (FRE without datawords) handling to not cause
      sframe_init_cfa_rule_data() and ultimately sframe_find() to fail
      with -EINVAL. (Sashiko AI)
    - sframe_init_[cfa_]rule_data(): Reject FRE control word with
      reserved_p=1. (Sashiko AI)
    - __find_fre(): Return RC of sframe_init_[cfa_]rule_data() if bad RC.
    - Normalize error code usage (.sframe is removed for all but ENOENT):
      ENOENT: No sframe or no FDE for IP found
              (FDE found but no FRE is EINVAL)
      EFAULT: Bad address
      EINVAL: Invalid input or sframe
    
    Changes in v14:
    - Rename __read_regular_fre_datawords() to
      __read_default_fre_datawords() to align to SFrame V3 specification
      (default FRE).
    - Rename SFRAME_FDE_TYPE_FLEXIBLE to SFRAME_FDE_TYPE_FLEX to match
      SFrame V3 specification and adjust to rename of SFRAME_FDE_TYPE_*.
    - Rename SFRAME_V3_FLEX_FDE_CTLWORD_*() to
      SFRAME_V3_FLEX_FDE_CTRLWORD_*() to match SFrame V3 reference
      implementation.
    - Add arch/*/include/asm/unwind_user_sframe.h to MAINTAINERS.

 MAINTAINERS            |   1 +
 kernel/unwind/sframe.c | 287 +++++++++++++++++++++++++++++++++--------
 kernel/unwind/sframe.h |   6 +
 3 files changed, 238 insertions(+), 56 deletions(-)

diff --git a/MAINTAINERS b/MAINTAINERS
index a9b42b67a88d..25f0b933511c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -27875,6 +27875,7 @@ M:	Josh Poimboeuf <jpoimboe@kernel.org>
 M:	Steven Rostedt <rostedt@goodmis.org>
 S:	Maintained
 F:	arch/*/include/asm/unwind_user.h
+F:	arch/*/include/asm/unwind_user_sframe.h
 F:	include/asm-generic/unwind_user.h
 F:	include/linux/sframe.h
 F:	include/linux/unwind*.h
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index daa97d8b0231..b623dca072da 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -12,6 +12,7 @@
 #include <linux/mm.h>
 #include <linux/string_helpers.h>
 #include <linux/sframe.h>
+#include <asm/unwind_user_sframe.h>
 #include <linux/unwind_user_types.h>
 
 #include "sframe.h"
@@ -31,8 +32,11 @@ struct sframe_fde_internal {
 struct sframe_fre_internal {
 	unsigned int	size;
 	u32		ip_off;
+	u32		cfa_ctl;
 	s32		cfa_off;
+	u32		ra_ctl;
 	s32		ra_off;
+	u32		fp_ctl;
 	s32		fp_off;
 	u8		info;
 };
@@ -200,19 +204,160 @@ static __always_inline int __find_fde(struct sframe_section *sec,
 		 s32 :	UNSAFE_GET_USER_SIGNED_INC(to, from, size, label),	\
 		 s64 :	UNSAFE_GET_USER_SIGNED_INC(to, from, size, label))
 
+static __always_inline int
+__read_default_fre_datawords(struct sframe_section *sec,
+			     struct sframe_fde_internal *fde,
+			     unsigned long cur,
+			     unsigned char dataword_count,
+			     unsigned char dataword_size,
+			     struct sframe_fre_internal *fre)
+{
+	s32 cfa_off, ra_off, fp_off;
+	unsigned int cfa_regnum;
+
+	UNSAFE_GET_USER_INC(cfa_off, cur, dataword_size, Efault);
+	dataword_count--;
+
+	ra_off = sec->ra_off;
+	if (!ra_off && dataword_count) {
+		dataword_count--;
+		UNSAFE_GET_USER_INC(ra_off, cur, dataword_size, Efault);
+	}
+
+	fp_off = sec->fp_off;
+	if (!fp_off && dataword_count) {
+		dataword_count--;
+		UNSAFE_GET_USER_INC(fp_off, cur, dataword_size, Efault);
+	}
+
+	if (dataword_count)
+		return -EINVAL;
+
+	cfa_regnum =
+		(SFRAME_V3_FRE_CFA_BASE_REG_ID(fre->info) == SFRAME_BASE_REG_FP) ?
+			SFRAME_REG_FP : SFRAME_REG_SP;
+
+	fre->cfa_ctl	= (cfa_regnum << 3) | 1; /* regnum, deref_p=0, reg_p=1 */
+	fre->cfa_off	= cfa_off;
+	fre->ra_ctl	= ra_off ? 2 : 0; /* regnum=0, deref_p=(ra_off != 0), reg_p=0 */
+	fre->ra_off	= ra_off;
+	fre->fp_ctl	= fp_off ? 2 : 0; /* regnum=0, deref_p=(fp_off != 0), reg_p=0 */
+	fre->fp_off	= fp_off;
+
+	return 0;
+
+Efault:
+	return -EFAULT;
+}
+
+static __always_inline int
+__read_flex_fde_fre_datawords(struct sframe_section *sec,
+			      struct sframe_fde_internal *fde,
+			      unsigned long cur,
+			      unsigned char dataword_count,
+			      unsigned char dataword_size,
+			      struct sframe_fre_internal *fre)
+{
+	u32 cfa_ctl, ra_ctl, fp_ctl;
+	s32 cfa_off, ra_off, fp_off;
+
+	if (dataword_count < 2)
+		return -EINVAL;
+	UNSAFE_GET_USER_INC(cfa_ctl, cur, dataword_size, Efault);
+	UNSAFE_GET_USER_INC(cfa_off, cur, dataword_size, Efault);
+	dataword_count -= 2;
+
+	/*
+	 * Each RA/FP location info consumes either two datawords
+	 * (control word + offset) or one padding word substituting
+	 * for that pair.  Padding is only valid as substitution if
+	 * followed by further non-padding location info.  Therefore
+	 * decoding only proceeds with at least two datawords.  Any
+	 * leftover trailing datawords are invalid and rejected by
+	 * the final check.
+	 */
+
+	ra_off = sec->ra_off;
+	ra_ctl = ra_off ? 2 : 0; /* regnum=0, deref_p=(ra_off != 0), reg_p=0 */
+	if (dataword_count >= 2) {
+		UNSAFE_GET_USER_INC(ra_ctl, cur, dataword_size, Efault);
+		dataword_count--;
+		if (ra_ctl) {
+			UNSAFE_GET_USER_INC(ra_off, cur, dataword_size, Efault);
+			dataword_count--;
+		} else {
+			/* Padding RA location info */
+			ra_ctl = ra_off ? 2 : 0; /* re-deduce (see above) */
+		}
+	}
+
+	fp_off = sec->fp_off;
+	fp_ctl = fp_off ? 2 : 0; /* regnum=0, deref_p=(fp_off != 0), reg_p=0 */
+	if (dataword_count >= 2) {
+		UNSAFE_GET_USER_INC(fp_ctl, cur, dataword_size, Efault);
+		dataword_count--;
+		if (fp_ctl) {
+			UNSAFE_GET_USER_INC(fp_off, cur, dataword_size, Efault);
+			dataword_count--;
+		} else {
+			/* Padding FP location info */
+			fp_ctl = fp_off ? 2 : 0; /* re-deduce (see above) */
+		}
+	}
+
+	/* Reject trailing padding or unknown extra datawords */
+	if (dataword_count)
+		return -EINVAL;
+
+	fre->cfa_ctl	= cfa_ctl;
+	fre->cfa_off	= cfa_off;
+	fre->ra_ctl	= ra_ctl;
+	fre->ra_off	= ra_off;
+	fre->fp_ctl	= fp_ctl;
+	fre->fp_off	= fp_off;
+
+	return 0;
+
+Efault:
+	return -EFAULT;
+}
+
+static __always_inline int
+__read_fre_datawords(struct sframe_section *sec,
+		     struct sframe_fde_internal *fde,
+		     unsigned long cur,
+		     unsigned char dataword_count,
+		     unsigned char dataword_size,
+		     struct sframe_fre_internal *fre)
+{
+	unsigned char fde_type = SFRAME_V3_FDE_TYPE(fde->info2);
+
+	switch (fde_type) {
+	case SFRAME_FDE_TYPE_DEFAULT:
+		return __read_default_fre_datawords(sec, fde, cur,
+						    dataword_count,
+						    dataword_size,
+						    fre);
+	case SFRAME_FDE_TYPE_FLEX:
+		return __read_flex_fde_fre_datawords(sec, fde, cur,
+						     dataword_count,
+						     dataword_size,
+						     fre);
+	default:
+		return -EINVAL;
+	}
+}
+
 static __always_inline int __read_fre(struct sframe_section *sec,
 				      struct sframe_fde_internal *fde,
 				      unsigned long fre_addr,
 				      struct sframe_fre_internal *fre)
 {
-	unsigned char fde_type = SFRAME_V3_FDE_TYPE(fde->info2);
 	unsigned char fde_pctype = SFRAME_V3_FDE_PCTYPE(fde->info);
 	unsigned char fre_type = SFRAME_V3_FDE_FRE_TYPE(fde->info);
 	unsigned char dataword_count, dataword_size;
-	s32 cfa_off, ra_off, fp_off;
 	unsigned long cur = fre_addr;
 	unsigned char addr_size;
-	unsigned int fre_size;
 	u32 ip_off;
 	u8 info;
 
@@ -233,80 +378,105 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	dataword_size  = dataword_size_enum_to_size(SFRAME_V3_FRE_DATAWORD_SIZE(info));
 	if (!dataword_size)
 		return -EINVAL;
-	fre_size = addr_size + 1 + (dataword_count * dataword_size);
 
 	if (cur + (dataword_count * dataword_size) > sec->fres_end)
 		return -EFAULT;
 
-	/* TODO: Support for flexible FDEs not implemented yet. */
-	if (fde_type != SFRAME_FDE_TYPE_DEFAULT)
-		return -EINVAL;
+	fre->size	= addr_size + 1 + (dataword_count * dataword_size);
+	fre->ip_off	= ip_off;
+	fre->info	= info;
 
 	if (!dataword_count) {
 		/*
-		 * A FRE without data words indicates RA undefined /
-		 * outermost frame.
+		 * A FRE without datawords indicates an outermost
+		 * frame.  Zero-initialize CFA, RA, and FP location
+		 * info, except for the CFA control word, so that
+		 * neither sframe_init_cfa_rule_data() nor
+		 * sframe_init_rule_data() fail.
 		 */
-		cfa_off	= 0;
-		ra_off	= 0;
-		fp_off	= 0;
-		goto done;
-	}
-
-	UNSAFE_GET_USER_INC(cfa_off, cur, dataword_size, Efault);
-	dataword_count--;
-
-	ra_off = sec->ra_off;
-	if (!ra_off && dataword_count) {
-		dataword_count--;
-		UNSAFE_GET_USER_INC(ra_off, cur, dataword_size, Efault);
-	}
+		fre->cfa_ctl	= (SFRAME_REG_SP << 3) | 1; /* regnum=SP, deref_p=0, reg_p=1 */
+		fre->cfa_off	= 0;
+		fre->ra_ctl	= 0;
+		fre->ra_off	= 0;
+		fre->fp_ctl	= 0;
+		fre->fp_off	= 0;
 
-	fp_off = sec->fp_off;
-	if (!fp_off && dataword_count) {
-		dataword_count--;
-		UNSAFE_GET_USER_INC(fp_off, cur, dataword_size, Efault);
+		return 0;
 	}
 
-	if (dataword_count)
-		return -EINVAL;
-
-done:
-	fre->size	= fre_size;
-	fre->ip_off	= ip_off;
-	fre->cfa_off	= cfa_off;
-	fre->ra_off	= ra_off;
-	fre->fp_off	= fp_off;
-	fre->info	= info;
-
-	return 0;
+	return __read_fre_datawords(sec, fde, cur, dataword_count, dataword_size, fre);
 
 Efault:
 	return -EFAULT;
 }
 
-static __always_inline void
+static __always_inline int
 sframe_init_cfa_rule_data(struct unwind_user_cfa_rule_data *cfa_rule_data,
-			  unsigned char fre_info,
-			  s32 offset)
+			  u32 ctlword, s32 offset)
 {
-	if (SFRAME_V3_FRE_CFA_BASE_REG_ID(fre_info) == SFRAME_BASE_REG_FP)
-		cfa_rule_data->rule = UNWIND_USER_CFA_RULE_FP_OFFSET;
-	else
+	bool deref_p = SFRAME_V3_FLEX_FDE_CTRLWORD_DEREF_P(ctlword);
+	bool reg_p = SFRAME_V3_FLEX_FDE_CTRLWORD_REG_P(ctlword);
+	bool reserved_p = SFRAME_V3_FLEX_FDE_CTRLWORD_RESERVED_P(ctlword);
+	unsigned int regnum = SFRAME_V3_FLEX_FDE_CTRLWORD_REGNUM(ctlword);
+
+	if (reserved_p)
+		return -EINVAL;
+
+	/* CFA recovery rule must be register-based */
+	if (!reg_p)
+		return -EINVAL;
+
+	switch (regnum) {
+	case SFRAME_REG_SP:
 		cfa_rule_data->rule = UNWIND_USER_CFA_RULE_SP_OFFSET;
+		break;
+	case SFRAME_REG_FP:
+		cfa_rule_data->rule = UNWIND_USER_CFA_RULE_FP_OFFSET;
+		break;
+	default:
+		cfa_rule_data->rule = UNWIND_USER_CFA_RULE_REG_OFFSET;
+		cfa_rule_data->regnum = regnum;
+	}
+
+	if (deref_p)
+		cfa_rule_data->rule |= UNWIND_USER_RULE_DEREF;
+
 	cfa_rule_data->offset = offset;
+
+	return 0;
 }
 
-static __always_inline void
+static __always_inline int
 sframe_init_rule_data(struct unwind_user_rule_data *rule_data,
-		      s32 offset)
+		      u32 ctlword, s32 offset)
 {
-	if (offset) {
-		rule_data->rule = UNWIND_USER_RULE_CFA_OFFSET_DEREF;
-		rule_data->offset = offset;
-	} else {
+	bool deref_p = SFRAME_V3_FLEX_FDE_CTRLWORD_DEREF_P(ctlword);
+	bool reg_p = SFRAME_V3_FLEX_FDE_CTRLWORD_REG_P(ctlword);
+	bool reserved_p = SFRAME_V3_FLEX_FDE_CTRLWORD_RESERVED_P(ctlword);
+
+	if (!ctlword && !offset) {
 		rule_data->rule = UNWIND_USER_RULE_RETAIN;
+		return 0;
+	}
+
+	if (reserved_p)
+		return -EINVAL;
+
+	if (reg_p) {
+		unsigned int regnum = SFRAME_V3_FLEX_FDE_CTRLWORD_REGNUM(ctlword);
+
+		rule_data->rule = UNWIND_USER_RULE_REG_OFFSET;
+		rule_data->regnum = regnum;
+	} else {
+		rule_data->rule = UNWIND_USER_RULE_CFA_OFFSET;
 	}
+
+	if (deref_p)
+		rule_data->rule |= UNWIND_USER_RULE_DEREF;
+
+	rule_data->offset = offset;
+
+	return 0;
 }
 
 static __always_inline int __find_fre(struct sframe_section *sec,
@@ -321,6 +491,7 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 	bool which = false;
 	unsigned int i;
 	u32 ip_off;
+	int ret;
 
 	ip_off = ip - fde->func_addr;
 
@@ -330,8 +501,6 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 	fre_addr = sec->fres_start + fde->fres_off;
 
 	for (i = 0; i < fde->fres_num; i++) {
-		int ret;
-
 		/*
 		 * Alternate between the two fre_addr[] entries for 'fre' and
 		 * 'prev_fre'.
@@ -358,9 +527,15 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 		return -EINVAL;
 	fre = prev_fre;
 
-	sframe_init_cfa_rule_data(&frame->cfa, fre->info, fre->cfa_off);
-	sframe_init_rule_data(&frame->ra, fre->ra_off);
-	sframe_init_rule_data(&frame->fp, fre->fp_off);
+	ret = sframe_init_cfa_rule_data(&frame->cfa, fre->cfa_ctl, fre->cfa_off);
+	if (ret)
+		return ret;
+	ret = sframe_init_rule_data(&frame->ra, fre->ra_ctl, fre->ra_off);
+	if (ret)
+		return ret;
+	ret = sframe_init_rule_data(&frame->fp, fre->fp_ctl, fre->fp_off);
+	if (ret)
+		return ret;
 	frame->outermost = SFRAME_V3_FRE_RA_UNDEFINED_P(fre->info);
 
 	return 0;
diff --git a/kernel/unwind/sframe.h b/kernel/unwind/sframe.h
index ed111fd0d702..1a2528e4b149 100644
--- a/kernel/unwind/sframe.h
+++ b/kernel/unwind/sframe.h
@@ -66,6 +66,7 @@ struct sframe_fda_v3 {
 #define SFRAME_V3_AARCH64_FDE_PAUTH_KEY(info)	(((info) >> 5) & 0x1)
 
 #define SFRAME_FDE_TYPE_DEFAULT			0
+#define SFRAME_FDE_TYPE_FLEX			1
 
 #define SFRAME_V3_FDE_TYPE_MASK			0x1f
 #define SFRAME_V3_FDE_TYPE(info2)		((info2) & SFRAME_V3_FDE_TYPE_MASK)
@@ -79,4 +80,9 @@ struct sframe_fda_v3 {
 #define SFRAME_V3_AARCH64_FRE_MANGLED_RA_P(info)	(((info) >> 7) & 0x1)
 #define SFRAME_V3_FRE_RA_UNDEFINED_P(info)		(SFRAME_V3_FRE_DATAWORD_COUNT(info) == 0)
 
+#define SFRAME_V3_FLEX_FDE_CTRLWORD_REGNUM(data)	(((data) >> 3) & 0x1f)
+#define SFRAME_V3_FLEX_FDE_CTRLWORD_RESERVED_P(data)	(((data) >> 2) & 0x1)
+#define SFRAME_V3_FLEX_FDE_CTRLWORD_DEREF_P(data)	(((data) >> 1) & 0x1)
+#define SFRAME_V3_FLEX_FDE_CTRLWORD_REG_P(data)		((data) & 0x1)
+
 #endif /* _SFRAME_H */
-- 
2.51.0

[PATCH v16 17/20] unwind_user/sframe: Separate reading of FRE from reading of FRE data words

[Jens Remus]

__find_fre() performs linear search for a matching SFrame FRE for a
given IP.  For that purpose it uses __read_fre(), which reads the whole
FRE.  That is the variable-size FRE structure as well as the trailing
variable-length array of variable-size data words.  For the search logic
to skip over the FRE it would be sufficient to read the variable-size
FRE structure only, which includes the count and size of data words.

Add fields to struct sframe_fre_internal to store the FRE data word's
address, count, and size.  Change __read_fre() to read the variable-
size FRE structure only and populate those new fields.  Change
__read_fre_datawords() to use those new fields.  Change __find_fre()
to use __read_fre_datawords() to read the FRE data words only after a
matching FRE has been found.  Introduce safe_read_fre_datawords() and
use it in sframe_validate_section() to validate that the FRE data words.

Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v15:
    - sframe_validate_section(): Fix format specifier for number of FREs
      in debug message. (Sashiko AI)
    
    Changes in v14:
    - Adjust to rename of SFRAME_FDE_TYPE_* and
      __read_default_fre_datawords().
    - Update function name in debug message.

 kernel/unwind/sframe.c | 99 +++++++++++++++++++++++++++---------------
 1 file changed, 63 insertions(+), 36 deletions(-)

diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index b623dca072da..7f439600b0f0 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -39,6 +39,9 @@ struct sframe_fre_internal {
 	u32		fp_ctl;
 	s32		fp_off;
 	u8		info;
+	unsigned long	dw_addr;
+	unsigned char	dw_count;
+	unsigned char	dw_size;
 };
 
 DEFINE_STATIC_SRCU(sframe_srcu);
@@ -207,11 +210,11 @@ static __always_inline int __find_fde(struct sframe_section *sec,
 static __always_inline int
 __read_default_fre_datawords(struct sframe_section *sec,
 			     struct sframe_fde_internal *fde,
-			     unsigned long cur,
-			     unsigned char dataword_count,
-			     unsigned char dataword_size,
 			     struct sframe_fre_internal *fre)
 {
+	unsigned char dataword_count = fre->dw_count;
+	unsigned char dataword_size = fre->dw_size;
+	unsigned long cur = fre->dw_addr;
 	s32 cfa_off, ra_off, fp_off;
 	unsigned int cfa_regnum;
 
@@ -253,11 +256,11 @@ __read_default_fre_datawords(struct sframe_section *sec,
 static __always_inline int
 __read_flex_fde_fre_datawords(struct sframe_section *sec,
 			      struct sframe_fde_internal *fde,
-			      unsigned long cur,
-			      unsigned char dataword_count,
-			      unsigned char dataword_size,
 			      struct sframe_fre_internal *fre)
 {
+	unsigned char dataword_count = fre->dw_count;
+	unsigned char dataword_size = fre->dw_size;
+	unsigned long cur = fre->dw_addr;
 	u32 cfa_ctl, ra_ctl, fp_ctl;
 	s32 cfa_off, ra_off, fp_off;
 
@@ -325,24 +328,34 @@ __read_flex_fde_fre_datawords(struct sframe_section *sec,
 static __always_inline int
 __read_fre_datawords(struct sframe_section *sec,
 		     struct sframe_fde_internal *fde,
-		     unsigned long cur,
-		     unsigned char dataword_count,
-		     unsigned char dataword_size,
 		     struct sframe_fre_internal *fre)
 {
 	unsigned char fde_type = SFRAME_V3_FDE_TYPE(fde->info2);
+	unsigned char dataword_count = fre->dw_count;
+
+	if (!dataword_count) {
+		/*
+		 * A FRE without datawords indicates an outermost
+		 * frame.  Zero-initialize CFA, RA, and FP location
+		 * info, except for the CFA control word, so that
+		 * neither sframe_init_cfa_rule_data() nor
+		 * sframe_init_rule_data() fail.
+		 */
+		fre->cfa_ctl	= (SFRAME_REG_SP << 3) | 1; /* regnum=SP, deref_p=0, reg_p=1 */
+		fre->cfa_off	= 0;
+		fre->ra_ctl	= 0;
+		fre->ra_off	= 0;
+		fre->fp_ctl	= 0;
+		fre->fp_off	= 0;
+
+		return 0;
+	}
 
 	switch (fde_type) {
 	case SFRAME_FDE_TYPE_DEFAULT:
-		return __read_default_fre_datawords(sec, fde, cur,
-						    dataword_count,
-						    dataword_size,
-						    fre);
+		return __read_default_fre_datawords(sec, fde, fre);
 	case SFRAME_FDE_TYPE_FLEX:
-		return __read_flex_fde_fre_datawords(sec, fde, cur,
-						     dataword_count,
-						     dataword_size,
-						     fre);
+		return __read_flex_fde_fre_datawords(sec, fde, fre);
 	default:
 		return -EINVAL;
 	}
@@ -385,26 +398,11 @@ static __always_inline int __read_fre(struct sframe_section *sec,
 	fre->size	= addr_size + 1 + (dataword_count * dataword_size);
 	fre->ip_off	= ip_off;
 	fre->info	= info;
+	fre->dw_addr	= cur;
+	fre->dw_count	= dataword_count;
+	fre->dw_size	= dataword_size;
 
-	if (!dataword_count) {
-		/*
-		 * A FRE without datawords indicates an outermost
-		 * frame.  Zero-initialize CFA, RA, and FP location
-		 * info, except for the CFA control word, so that
-		 * neither sframe_init_cfa_rule_data() nor
-		 * sframe_init_rule_data() fail.
-		 */
-		fre->cfa_ctl	= (SFRAME_REG_SP << 3) | 1; /* regnum=SP, deref_p=0, reg_p=1 */
-		fre->cfa_off	= 0;
-		fre->ra_ctl	= 0;
-		fre->ra_off	= 0;
-		fre->fp_ctl	= 0;
-		fre->fp_off	= 0;
-
-		return 0;
-	}
-
-	return __read_fre_datawords(sec, fde, cur, dataword_count, dataword_size, fre);
+	return 0;
 
 Efault:
 	return -EFAULT;
@@ -527,6 +525,10 @@ static __always_inline int __find_fre(struct sframe_section *sec,
 		return -EINVAL;
 	fre = prev_fre;
 
+	ret = __read_fre_datawords(sec, fde, fre);
+	if (ret)
+		return ret;
+
 	ret = sframe_init_cfa_rule_data(&frame->cfa, fre->cfa_ctl, fre->cfa_off);
 	if (ret)
 		return ret;
@@ -610,6 +612,20 @@ static int safe_read_fre(struct sframe_section *sec,
 	return ret;
 }
 
+static int safe_read_fre_datawords(struct sframe_section *sec,
+				   struct sframe_fde_internal *fde,
+				   struct sframe_fre_internal *fre)
+{
+	int ret;
+
+	if (!user_read_access_begin((void __user *)sec->sframe_start,
+				    sec->sframe_end - sec->sframe_start))
+		return -EFAULT;
+	ret = __read_fre_datawords(sec, fde, fre);
+	user_read_access_end();
+	return ret;
+}
+
 static int sframe_validate_section(struct sframe_section *sec)
 {
 	struct sframe_fde_internal fde;
@@ -648,6 +664,17 @@ static int sframe_validate_section(struct sframe_section *sec)
 					fde.rep_size);
 				return ret;
 			}
+			ret = safe_read_fre_datawords(sec, &fde, &fre);
+			if (ret) {
+				dbg_sec("FDE %u: safe_read_fre_datawords(%u) failed\n", i, j);
+				dbg_sec("FDE: func_addr:%#lx func_size:%#x fda_off:%#x fres_off:%#x fres_num:%u info:%u info2:%u rep_size:%u\n",
+					fde.func_addr, fde.func_size,
+					fde.fda_off,
+					fde.fres_off, fde.fres_num,
+					fde.info, fde.info2,
+					fde.rep_size);
+				return ret;
+			}
 
 			if (j && fre.ip_off <= prev_ip_off) {
 				dbg_sec("FDE %u: FRE %u not sorted\n", i, j);
-- 
2.51.0

[PATCH v16 18/20] unwind_user/sframe: Duplicate registered .sframe section data on clone/fork

[Jens Remus]

When duplicating a process' virtual memory mappings also duplicate all
of its registered .sframe sections stored in the per-mm maple tree to
enable stacktracing using sframe of the child process.

Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v16:
    - dup_mmap(): Drop unnecessary CONFIG_HAVE_UNWIND_USER_SFRAME #ifdefs.
      (Sashiko AI)
    - dup_mmap(): Call sframe_dup_mm() prior to arch_dup_mmap(), so that
      comes last.
    
    Changes in v15:
    - New patch.

 include/linux/sframe.h       |  5 ++++
 kernel/unwind/sframe.c       | 48 ++++++++++++++++++++++++++++++++++++
 kernel/unwind/sframe_debug.h |  7 ++++++
 mm/mmap.c                    |  5 ++++
 4 files changed, 65 insertions(+)

diff --git a/include/linux/sframe.h b/include/linux/sframe.h
index b79c5ec09229..91889b4fe3dd 100644
--- a/include/linux/sframe.h
+++ b/include/linux/sframe.h
@@ -28,6 +28,7 @@ struct sframe_section {
 };
 
 #define INIT_MM_SFRAME .sframe_mt = MTREE_INIT(sframe_mt, 0),
+extern int sframe_dup_mm(struct mm_struct *mm, struct mm_struct *oldmm);
 extern void sframe_free_mm(struct mm_struct *mm);
 
 extern int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
@@ -45,6 +46,10 @@ static inline bool current_has_sframe(void)
 #else /* !CONFIG_HAVE_UNWIND_USER_SFRAME */
 
 #define INIT_MM_SFRAME
+static inline int sframe_dup_mm(struct mm_struct *mm, struct mm_struct *oldmm)
+{
+	return 0;
+}
 static inline void sframe_free_mm(struct mm_struct *mm) {}
 static inline int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
 				     unsigned long text_start, unsigned long text_end)
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 7f439600b0f0..db88d993dff1 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -875,6 +875,54 @@ int sframe_remove_section(unsigned long sframe_start)
 	return 0;
 }
 
+static void __sframe_dup_section(struct sframe_section *sec, struct sframe_section *oldsec)
+{
+	sec->sframe_start	= oldsec->sframe_start;
+	sec->sframe_end		= oldsec->sframe_end;
+	sec->text_start		= oldsec->text_start;
+	sec->text_end		= oldsec->text_end;
+
+	sec->fdes_start		= oldsec->fdes_start;
+	sec->fres_start		= oldsec->fres_start;
+	sec->fres_end		= oldsec->fres_end;
+	sec->num_fdes		= oldsec->num_fdes;
+
+	sec->ra_off		= oldsec->ra_off;
+	sec->fp_off		= oldsec->fp_off;
+
+	dbg_dup(sec, oldsec);
+}
+
+int sframe_dup_mm(struct mm_struct *mm, struct mm_struct *oldmm)
+{
+	struct sframe_section *sec, *oldsec;
+	unsigned long index = 0;
+	int ret;
+
+	guard(srcu)(&sframe_srcu);
+
+	mt_for_each(&oldmm->sframe_mt, oldsec, index, ULONG_MAX) {
+		sec = kzalloc(sizeof(*sec), GFP_KERNEL_ACCOUNT);
+		if (!sec)
+			return -ENOMEM;
+
+		__sframe_dup_section(sec, oldsec);
+
+		ret = mtree_insert_range(&mm->sframe_mt,
+					 sec->text_start,
+					 sec->text_end - 1,
+					 sec, GFP_KERNEL_ACCOUNT);
+		if (ret)
+			goto err_free;
+	}
+
+	return 0;
+
+err_free:
+	free_section(sec);
+	return ret;
+}
+
 void sframe_free_mm(struct mm_struct *mm)
 {
 	struct sframe_section *sec;
diff --git a/kernel/unwind/sframe_debug.h b/kernel/unwind/sframe_debug.h
index a63e75cccc70..2503972155e8 100644
--- a/kernel/unwind/sframe_debug.h
+++ b/kernel/unwind/sframe_debug.h
@@ -48,6 +48,12 @@ static inline void dbg_init(struct sframe_section *sec)
 		sec->filename = kstrdup("(anonymous)", GFP_KERNEL_ACCOUNT);
 }
 
+static inline void dbg_dup(struct sframe_section *sec, struct sframe_section *oldsec)
+{
+	if (oldsec->filename)
+		sec->filename = kstrdup(oldsec->filename, GFP_KERNEL_ACCOUNT);
+}
+
 static inline void dbg_free(struct sframe_section *sec)
 {
 	kfree(sec->filename);
@@ -61,6 +67,7 @@ static inline void dbg_free(struct sframe_section *sec)
 static inline void dbg_print_header(struct sframe_section *sec) {}
 
 static inline void dbg_init(struct sframe_section *sec) {}
+static inline void dbg_dup(struct sframe_section *sec, struct sframe_section *oldsec) {}
 static inline void dbg_free(struct sframe_section *sec) {}
 
 #endif /* !CONFIG_DYNAMIC_DEBUG */
diff --git a/mm/mmap.c b/mm/mmap.c
index 5754d1c36462..8715be691488 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -48,6 +48,7 @@
 #include <linux/sched/mm.h>
 #include <linux/ksm.h>
 #include <linux/memfd.h>
+#include <linux/sframe.h>
 
 #include <linux/uaccess.h>
 #include <asm/cacheflush.h>
@@ -1844,6 +1845,9 @@ __latent_entropy int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 			goto loop_out;
 		}
 	}
+	retval = sframe_dup_mm(mm, oldmm);
+	if (retval)
+		goto loop_out;
 	/* a new mm has just been created */
 	retval = arch_dup_mmap(oldmm, mm);
 loop_out:
@@ -1893,6 +1897,7 @@ __latent_entropy int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 			vm_unacct_memory(charge);
 		}
 		__mt_destroy(&mm->mm_mt);
+		sframe_free_mm(mm);
 		/*
 		 * The mm_struct is going to exit, but the locks will be dropped
 		 * first.  Set the mm_struct as unstable is advisable as it is
-- 
2.51.0

[PATCH v16 19/20] unwind_user/sframe/x86: Enable sframe unwinding on x86

[Jens Remus]

From: Josh Poimboeuf <jpoimboe@kernel.org>

The x86 SFrame V3 implementation works fairly well, starting with
binutils 2.46.  Enable it.

[ Jens Remus: Reword commit message for SFrame V3, starting with
binutils 2.46. ]

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v15:
    - unwind_user_get_reg(): Fail if !user_64bit_mode(). (Sashiko AI)
    - unwind_user_get_reg(): Simplify guarding using CONFIG_X86_64.
    - unwind_user_get_reg(): Add pr_debug_once() if unsupported register
      number.
    
    Changes in v14:
    - Drop superfluous empty line in unwind_user_get_reg().
    
    Changes in v13:
    - Naive implementation of unwind_user_get_reg() to support SFrame V3
      flexible FDEs (e.g. used to represent DRAP pattern).
    - Define SFRAME_REG_SP and SFRAME_REG_FP to the respective x86-64
      DWARF register numbers.
    - Reword commit message for SFrame V3 and (upcoming) binutils 2.46.

 arch/x86/Kconfig                          |  1 +
 arch/x86/include/asm/unwind_user.h        | 39 +++++++++++++++++++++++
 arch/x86/include/asm/unwind_user_sframe.h | 12 +++++++
 3 files changed, 52 insertions(+)
 create mode 100644 arch/x86/include/asm/unwind_user_sframe.h

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f3f7cb01d69d..51286dfdb5f4 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -302,6 +302,7 @@ config X86
 	select HAVE_UACCESS_VALIDATION		if HAVE_OBJTOOL
 	select HAVE_UNSTABLE_SCHED_CLOCK
 	select HAVE_UNWIND_USER_FP		if X86_64
+	select HAVE_UNWIND_USER_SFRAME		if X86_64
 	select HAVE_USER_RETURN_NOTIFIER
 	select HAVE_GENERIC_VDSO
 	select VDSO_GETRANDOM			if X86_64
diff --git a/arch/x86/include/asm/unwind_user.h b/arch/x86/include/asm/unwind_user.h
index f38f7c5ff1de..942475235431 100644
--- a/arch/x86/include/asm/unwind_user.h
+++ b/arch/x86/include/asm/unwind_user.h
@@ -15,6 +15,45 @@ static inline int unwind_user_word_size(struct pt_regs *regs)
 	return user_64bit_mode(regs) ? 8 : 4;
 }
 
+#ifdef CONFIG_X86_64
+
+static inline int unwind_user_get_reg(unsigned long *val, unsigned int regnum)
+{
+	struct pt_regs *regs = task_pt_regs(current);
+
+	/* SFrame only supports x86-64 */
+	if (!user_64bit_mode(regs))
+		return -EINVAL;
+
+	switch (regnum) {
+	/* DWARF register numbers 0..15 */
+	case  0: *val = regs->ax; break;
+	case  1: *val = regs->dx; break;
+	case  2: *val = regs->cx; break;
+	case  3: *val = regs->bx; break;
+	case  4: *val = regs->si; break;
+	case  5: *val = regs->di; break;
+	case  6: *val = regs->bp; break;
+	case  7: *val = regs->sp; break;
+	case  8: *val = regs->r8; break;
+	case  9: *val = regs->r9; break;
+	case 10: *val = regs->r10; break;
+	case 11: *val = regs->r11; break;
+	case 12: *val = regs->r12; break;
+	case 13: *val = regs->r13; break;
+	case 14: *val = regs->r14; break;
+	case 15: *val = regs->r15; break;
+	default:
+		pr_debug_once("%s (%d): unwind_user_get_reg(%u): unsupported register number\n",
+			      current->comm, current->pid, regnum);
+		return -EINVAL;
+	}
+	return 0;
+}
+#define unwind_user_get_reg unwind_user_get_reg
+
+#endif /* CONFIG_X86_64 */
+
 #endif /* CONFIG_UNWIND_USER */
 
 #ifdef CONFIG_HAVE_UNWIND_USER_FP
diff --git a/arch/x86/include/asm/unwind_user_sframe.h b/arch/x86/include/asm/unwind_user_sframe.h
new file mode 100644
index 000000000000..d828ae1a4aac
--- /dev/null
+++ b/arch/x86/include/asm/unwind_user_sframe.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_UNWIND_USER_SFRAME_H
+#define _ASM_X86_UNWIND_USER_SFRAME_H
+
+#ifdef CONFIG_X86_64
+
+#define SFRAME_REG_SP	7
+#define SFRAME_REG_FP	6
+
+#endif
+
+#endif /* _ASM_X86_UNWIND_USER_SFRAME_H */
-- 
2.51.0

[PATCH v16 20/20] unwind_user/sframe: Add prctl() interface for registering .sframe sections

[Jens Remus]

From: Josh Poimboeuf <jpoimboe@kernel.org>

The kernel doesn't have direct visibility to the ELF contents of shared
libraries.  Add some prctl() interfaces which allow glibc to tell the
kernel where to find .sframe sections.

[
  This adds an interface for prctl() for testing loading of sframes for
  libraries. But this interface should really be a system call. This patch
  is for testing purposes only and should not be applied to mainline.
]

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Indu Bhagat <ibhagatgnu@gmail.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v15:
    - Fix rebase error (missing break). (Sashiko AI)
    
    Changes in v14:
    - Bump PR_ADD_SFRAME and PR_REMOVE_SFRAME.

 include/uapi/linux/prctl.h | 4 ++++
 kernel/sys.c               | 9 +++++++++
 2 files changed, 13 insertions(+)

diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index b6ec6f693719..bd0bf828b033 100644
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -416,4 +416,8 @@ struct prctl_mm_map {
 # define PR_CFI_DISABLE		_BITUL(1)
 # define PR_CFI_LOCK		_BITUL(2)
 
+/* SFRAME management */
+#define PR_ADD_SFRAME			82
+#define PR_REMOVE_SFRAME		83
+
 #endif /* _LINUX_PRCTL_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index 62e842055cc9..b0a9b1e3ccd7 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -65,6 +65,7 @@
 #include <linux/rcupdate.h>
 #include <linux/uidgid.h>
 #include <linux/cred.h>
+#include <linux/sframe.h>
 
 #include <linux/nospec.h>
 
@@ -2907,6 +2908,14 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 		if (arg3 & PR_CFI_LOCK && !(arg3 & PR_CFI_DISABLE))
 			error = arch_prctl_lock_branch_landing_pad_state(me);
 		break;
+	case PR_ADD_SFRAME:
+		error = sframe_add_section(arg2, arg3, arg4, arg5);
+		break;
+	case PR_REMOVE_SFRAME:
+		if (arg3 || arg4 || arg5)
+			return -EINVAL;
+		error = sframe_remove_section(arg2);
+		break;
 	default:
 		trace_task_prctl_unknown(option, arg2, arg3, arg4, arg5);
 		error = -EINVAL;
-- 
2.51.0

Re: [PATCH v16 08/20] unwind_user: Stop when reaching an outermost frame

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The newly added `outermost` field in `struct unwind_user_frame` is left uninitialized in `unwind_user_next_sframe()`, causing `unwind_user_next_common()` to read stack garbage and potentially terminate unwinding prematurely.
--

commit 88bb99c2143c88573eb3287429d12baa8f4ccda7
Author: Jens Remus <jremus@linux.ibm.com>

unwind_user: Stop when reaching an outermost frame

This commit adds an indication for an outermost frame to the unwind user
frame structure. It updates the common user unwinding code to stop when
such a frame is encountered.

[ ... ]

> diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
> index 1fb2724197332..fdb1001e37505 100644
> --- a/kernel/unwind/user.c
> +++ b/kernel/unwind/user.c
> @@ -32,6 +32,12 @@ static int unwind_user_next_common(struct unwind_user_state *state,
>  {
>  	unsigned long cfa, fp, ra;
>  
> +	/* Stop unwinding when reaching an outermost frame. */
> +	if (frame->outermost) {

[Severity: Medium]
Could this read uninitialized stack memory during bisection?

In unwind_user_next_sframe(), struct unwind_user_frame frame is declared
on the stack without being fully zeroed. It then calls __find_fre() which
populates only some fields, leaving the new outermost field uninitialized:

unwind_user_next_sframe()
   struct unwind_user_frame frame;
   
   __find_fre()
      /* populates cfa_off, ra_off, fp_off, use_fp */

   unwind_user_next_common()
      if (frame->outermost) { /* reads uninitialized stack memory */

If the stack memory happens to be non-zero, this could incorrectly set
state->done = true and truncate the stack trace prematurely.

While this appears to be resolved in the subsequent commit
"unwind_user/sframe: Add support for outermost frame indication", does
introducing the read here before the initialization break bisectability?

> +		state->done = true;
> +		return 0;
> +	}
> +
>  	/* Get the Canonical Frame Address (CFA) */

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260521142546.3908498-1-jremus@linux.ibm.com?part=8

Re: [PATCH v16 02/20] unwind_user/sframe: Add support for reading .sframe headers

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Calculations for sframe section boundaries lack overflow checks, allowing malformed headers to bypass bounds validation on 32-bit architectures.
--

commit 054ec0b1d4b6a41d4be90015daaf62a201f3ec3b
Author: Josh Poimboeuf <jpoimboe@kernel.org>

unwind_user/sframe: Add support for reading .sframe headers

This commit introduces basic infrastructure for unwinding user space stacks
with sframe. It adds functionality to read and validate the .sframe section
header from user memory.

Link: https://lore.kernel.org/all/f27e8463783febfa0dabb0432a3dd6be8ad98412.1737511963.git.jpoimboe@kernel.org/

> diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
> new file mode 100644
> index 0000000000000..d24e9d4f8bef7
> --- /dev/null
> +++ b/kernel/unwind/sframe.c
> @@ -0,0 +1,136 @@
[ ... ]
> +static int sframe_read_header(struct sframe_section *sec)
> +{
> +	unsigned long header_end, fdes_start, fdes_end, fres_start, fres_end;
> +	struct sframe_header shdr;
> +	unsigned int num_fdes;
[ ... ]
> +	num_fdes   = shdr.num_fdes;
> +	fdes_start = header_end + shdr.fdes_off;
> +	fdes_end   = fdes_start + (num_fdes * sizeof(struct sframe_fde_v3));
> +
> +	fres_start = header_end + shdr.fres_off;
> +	fres_end   = fres_start + shdr.fre_len;

[Severity: High]
Could this introduce a regression on 32-bit architectures where these
boundary calculations overflow?

On 32-bit systems, operations like header_end + shdr.fdes_off and
num_fdes * sizeof(struct sframe_fde_v3) can overflow and wrap around to
small values. For example, if a malformed header sets num_fdes = 0x10000000,
the multiplication by 16 evaluates to 0.

This might allow a crafted sframe header to satisfy the subsequent
fres_start < fdes_end and fres_end <= sec->sframe_end checks, storing a
deceptively large num_fdes and out-of-bounds section pointers. When the kernel
unwinder later processes this section, it could attempt to iterate over
millions of entries or read from wrapped addresses, potentially causing CPU
stalls or soft lockups.

Could safe math helpers like check_add_overflow() or size_mul() be used
here to prevent silent wrap-arounds?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260521142546.3908498-1-jremus@linux.ibm.com?part=2

Re: [PATCH v16 07/20] unwind_user/sframe: Wire up unwind_user to sframe

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Missing instruction pointer adjustment for return addresses during SFrame unwinding of non-topmost frames.
--

commit 9e76c3f974e7ef0d88d0ca8c60fa84ef664ebee7
Author: Josh Poimboeuf <jpoimboe@kernel.org>

unwind_user/sframe: Wire up unwind_user to sframe

Now that the sframe infrastructure is fully in place, make it work by hooking
it up to the unwind_user interface.

> diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
> index 90ab3c1a205ef..1fb2724197332 100644
> --- a/kernel/unwind/user.c
> +++ b/kernel/unwind/user.c

[ ... ]

> @@ -82,6 +83,16 @@ static int unwind_user_next_fp(struct unwind_user_state *state)
>  	return unwind_user_next_common(state, &fp_frame);
>  }
>  
> +static int unwind_user_next_sframe(struct unwind_user_state *state)
> +{
> +	struct unwind_user_frame frame;
> +
> +	/* sframe expects the frame to be local storage */
> +	if (sframe_find(state->ip, &frame))

[Severity: Medium]
For non-topmost stack frames, state->ip holds the return address, which points
to the instruction after the call. If a call is the very last instruction of a
function (like a call to a noreturn function), the return address will point to
the first instruction of the next contiguous function in memory.

Could sframe_find() incorrectly match the next function's FDE and apply its
unwind rules to the current frame? Other table-driven unwinders handle this
by subtracting 1 from the instruction pointer for non-topmost frames.

> +		return -ENOENT;
> +	return unwind_user_next_common(state, &frame);
> +}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260521142546.3908498-1-jremus@linux.ibm.com?part=7

Re: [PATCH v16 12/20] unwind_user/sframe: Add .sframe validation option

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] The `.sframe` validation loop in `sframe_validate_section` lacks `cond_resched()`, allowing maliciously large or crafted `.sframe` sections to cause CPU soft lockups.
--

commit 134a5da326c64a7bfc6e8145805fff7efe4a4cc1
Author: Josh Poimboeuf <jpoimboe@kernel.org>
unwind_user/sframe: Add .sframe validation option

This commit introduces a debug feature to validate all .sframe sections
when first loading the file rather than on demand. The feature reads the
entire .sframe section for every loaded executable and shared library.

> diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
> index 2cfa274cd8dcf..e6d66ae8e7ac6 100644
> --- a/kernel/unwind/sframe.c
> +++ b/kernel/unwind/sframe.c

[ ... ]

> @@ -384,6 +384,94 @@ int sframe_find(unsigned long ip, struct unwind_user_frame *frame)
>  	goto end;
>  }
>  
> +#ifdef CONFIG_SFRAME_VALIDATION

[ ... ]

> +static int sframe_validate_section(struct sframe_section *sec)
> +{
> +	struct sframe_fde_internal fde;
> +	unsigned long prev_func_addr;
> +	unsigned int i;
> +
> +	for (i = 0; i < sec->num_fdes; i++) {
> +		struct sframe_fre_internal fre;
> +		unsigned long fre_addr;
> +		u32 prev_ip_off;
> +		unsigned int j;
> +		int ret;
> +
> +		ret = safe_read_fde(sec, i, &fde);
> +		if (ret) {
> +			dbg_sec("safe_read_fde(%u) failed\n", i);
> +			return ret;
> +		}
> +
> +		if (i && fde.func_addr <= prev_func_addr) {
> +			dbg_sec("FDE %u not sorted\n", i);
> +			return -EINVAL;
> +		}
> +		prev_func_addr = fde.func_addr;
> +
> +		fre_addr = sec->fres_start + fde.fres_off;
> +		for (j = 0; j < fde.fres_num; j++) {
> +			ret = safe_read_fre(sec, &fde, fre_addr, &fre);

[Severity: High]
Could a large or crafted .sframe section cause a CPU soft lockup here?

Since sec->num_fdes and fde.fres_num are bounded only by the mapped user
memory region size, a .sframe section could be crafted with millions of FDEs
pointing to the same valid array of FREs.

Without a cond_resched() or fatal_signal_pending() check in these nested
loops, iterating over these entries could monopolize the CPU in kernel mode
without yielding, potentially triggering the soft lockup watchdog.

> +			if (ret) {
> +				dbg_sec("FDE %u: safe_read_fre(%u) failed\n", i, j);
> +				dbg_sec("FDE: func_addr:%#lx func_size:%#x fda_off:%#x fres_off:%#x fres_num:%u info:%u info2:%u rep_size:%u\n",
> +					fde.func_addr, fde.func_size,
> +					fde.fda_off,
> +					fde.fres_off, fde.fres_num,
> +					fde.info, fde.info2,
> +					fde.rep_size);
> +				return ret;
> +			}

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260521142546.3908498-1-jremus@linux.ibm.com?part=12

Re: [PATCH v16 03/20] unwind_user/sframe: Store .sframe section data in per-mm maple tree

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 5 potential issue(s) to consider:
- [High] Concurrent `sframe_remove_section` calls lead to a TOCTOU race causing SRCU double-queueing and memory leaks.
- [High] The `sframe_mt` maple tree is initialized without `MT_FLAGS_USE_RCU`, causing use-after-free during lockless traversal.
- [High] `sframe_free_mm()` bypasses SRCU and synchronously frees objects, racing with concurrent SRCU readers.
- [Low] Mixing `scoped_guard()` with goto-based error handling violates subsystem cleanup rules.
- [Low] `current_has_sframe()` dereferences `current->mm` without including `<linux/sched.h>`, causing incomplete type errors.
--

commit 4b0aee91d63748e3221127b74ad789be7e3d2c6b
Author: Josh Poimboeuf <jpoimboe@kernel.org>
Subject: unwind_user/sframe: Store .sframe section data in per-mm maple tree

Associate an .sframe section with its mm by adding it to a per-mm maple
tree which is indexed by the corresponding text address range.  A single
.sframe section can be associated with multiple text ranges.

> diff --git a/include/linux/sframe.h b/include/linux/sframe.h
> index 0642595534f95..38047760e252e 100644
> --- a/include/linux/sframe.h
> +++ b/include/linux/sframe.h
> @@ -19,18 +24,31 @@ struct sframe_section {
>  	signed char	fp_off;
>  };
>  
> +#define INIT_MM_SFRAME .sframe_mt = MTREE_INIT(sframe_mt, 0),

[Severity: High]
Does this maple tree initialization need the MT_FLAGS_USE_RCU flag?

Since sframe_remove_section() traverses the tree locklessly using
mt_for_each(), omitting the RCU flag means internal tree nodes split or
merged by concurrent updates could be freed immediately via
kmem_cache_free(), potentially causing a use-after-free for the
lockless readers.

> +extern void sframe_free_mm(struct mm_struct *mm);
> +
>  extern int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
>  			      unsigned long text_start, unsigned long text_end);
>  extern int sframe_remove_section(unsigned long sframe_addr);
>  
> +static inline bool current_has_sframe(void)
> +{
> +	struct mm_struct *mm = current->mm;
> +
> +	return mm && !mtree_empty(&mm->sframe_mt);
> +}

[Severity: Low]
Will this compile cleanly in all contexts?

The header dereferences current->mm, but <linux/sched.h> doesn't appear
to be included here. Files including <linux/sframe.h> without also
including sched.h might fail to compile with incomplete type errors.

> diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
> index d24e9d4f8bef7..46dba3cb016df 100644
> --- a/kernel/unwind/sframe.c
> +++ b/kernel/unwind/sframe.c
[ ... ]
> @@ -122,15 +125,74 @@ int sframe_add_section(unsigned long sframe_start, unsigned long sframe_end,
>  	if (ret)
>  		goto err_free;
>  
> -	/* TODO nowhere to store it yet - just free it and return an error */
> -	ret = -ENOSYS;
> +	ret = mtree_insert_range(sframe_mt, sec->text_start, sec->text_end - 1,
> +				 sec, GFP_KERNEL_ACCOUNT);
> +	if (ret) {
> +		dbg("mtree_insert_range failed: text=%lx-%lx\n",
> +		    sec->text_start, sec->text_end);
> +		goto err_free;
> +	}
> +
> +	return 0;
>  
>  err_free:
>  	free_section(sec);
>  	return ret;
>  }

[Severity: Low]
This isn't a bug, but does mixing goto-based error handling (err_free)
with the scoped_guard() used earlier in this function violate the
cleanup subsystem guidelines?

The standard suggests managing the sec pointer via __free(kfree) instead
of using goto labels to avoid confusing ownership semantics.

> +static int __sframe_remove_section(struct mm_struct *mm,
> +				   struct sframe_section *sec)
> +{
> +	if (!mtree_erase(&mm->sframe_mt, sec->text_start)) {
> +		dbg("mtree_erase failed: text=%lx\n", sec->text_start);
> +		return -EINVAL;
> +	}
> +
> +	call_srcu(&sframe_srcu, &sec->rcu, sframe_free_srcu);
> +
> +	return 0;
> +}

[Severity: High]
Could this lockless tree access result in corrupting the SRCU callback
list and leaking memory?

If a concurrent thread inserts a new section at the same text_start
address before mtree_erase() is called, mtree_erase() will successfully
remove and return the new section.

Because the return value of mtree_erase() is not checked against sec,
the code proceeds to call call_srcu() on the original sec pointer. This
could double-queue the old section's RCU head and permanently leak the
newly inserted section.

[ ... ]
> +void sframe_free_mm(struct mm_struct *mm)
> +{
> +	struct sframe_section *sec;
> +	unsigned long index = 0;
> +
> +	if (!mm)
> +		return;
> +
> +	mt_for_each(&mm->sframe_mt, sec, index, ULONG_MAX)
> +		free_section(sec);
> +
> +	mtree_destroy(&mm->sframe_mt);
>  }

[Severity: High]
Does bypassing the SRCU grace period here cause a use-after-free for
concurrent readers?

If an unwinder accesses a section under sframe_srcu and then drops its
mm reference, triggering teardown, the synchronous free_section()
(which calls kfree directly) will free the section while the unwinder
is still relying on SRCU to keep it alive. Should this teardown path
use call_srcu() as well?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260521142546.3908498-1-jremus@linux.ibm.com?part=3

Re: [PATCH v16 11/20] unwind_user/sframe: Show file name in debug output

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:

New issues:
- [Low] VMA Classification Bug in `dbg_init()`

Pre-existing issues:
- [High] Calling `sframe_remove_section()` upon `-EFAULT` causes a deadlock in NMI context.
- [High] User-triggerable WARN_ON_ONCE in `sframe_find()` due to concurrent removal of malformed `.sframe` sections.
--

commit fff3b1ad1d5f40f0ff8ee5d6dd0af4160fc5f674
Author: Josh Poimboeuf <jpoimboe@kernel.org>

unwind_user/sframe: Show file name in debug output

This commit enhances sframe debugging by prefixing debug output strings
with the file name corresponding to the .sframe section.

> diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
> index e0eb2adf5a074..2cfa274cd8dcf 100644
> --- a/kernel/unwind/sframe.c
> +++ b/kernel/unwind/sframe.c

[ ... ]

> @@ -372,8 +372,10 @@ int sframe_find(unsigned long ip, struct unwind_user_frame *frame)
>  	}
>  
>  end:
> -	if (ret && ret != -ENOENT)
> +	if (ret && ret != -ENOENT) {
> +		dbg_sec("removing bad .sframe section\n");
>  		WARN_ON_ONCE(sframe_remove_section(sec->sframe_start));

[Severity: High]
This is a pre-existing issue, but can this error path cause a deadlock in
NMI context?

sframe_find() is a core unwinder function frequently invoked by perf PMU
interrupts, which execute in NMI context. If reading the user memory
fails, scoped_user_read_access_size() returns -EFAULT. This handler treats
it as a corrupted section and calls sframe_remove_section(), which
eventually calls mtree_erase() and acquires the maple tree spinlock.

Taking a non-irqsafe spinlock in NMI context violates kernel locking rules
and will immediately deadlock if the interrupted thread holds the same lock.
Could an unprivileged user exploit this to trigger a local denial of service?

[Severity: High]
This is also a pre-existing issue, but is it safe to unconditionally call
WARN_ON_ONCE(sframe_remove_section(...)) here?

If multiple threads concurrently trigger unwinding on a malformed or recently
unmapped .sframe section, they could all reach this error path simultaneously
under the SRCU read lock.

The first thread successfully removes the section, but subsequent threads will
fail to find it, causing sframe_remove_section() to return an error like
-EINVAL. This triggers the WARN_ON_ONCE, which can trivially panic the system
on kernels with panic_on_warn enabled.

> +	}
>  
>  	return ret;

[ ... ]

> diff --git a/kernel/unwind/sframe_debug.h b/kernel/unwind/sframe_debug.h
> index 36352124cde81..a63e75cccc700 100644
> --- a/kernel/unwind/sframe_debug.h
> +++ b/kernel/unwind/sframe_debug.h

[ ... ]

> +static inline void dbg_init(struct sframe_section *sec)
> +{
> +	struct mm_struct *mm = current->mm;
> +	struct vm_area_struct *vma;
> +
> +	guard(mmap_read_lock)(mm);
> +	vma = vma_lookup(mm, sec->sframe_start);
> +	if (!vma)
> +		sec->filename = kstrdup("(vma gone???)", GFP_KERNEL_ACCOUNT);
> +	else if (vma->vm_file)

[Severity: Low]
Does this correctly classify file-backed VMAs?

The MM subsystem guidelines state that vma->vm_file shouldn't be used as a
proxy for file-backed classification, because anonymous mappings (like private
mappings of /dev/zero created by some drivers) can still have vm_file set.

Should this use !vma_is_anonymous(vma) instead?

> +		sec->filename = kstrdup_quotable_file(vma->vm_file, GFP_KERNEL_ACCOUNT);
> +	else if (vma->vm_ops && vma->vm_ops->name)
> +		sec->filename = kstrdup(vma->vm_ops->name(vma), GFP_KERNEL_ACCOUNT);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260521142546.3908498-1-jremus@linux.ibm.com?part=11

Re: [PATCH v16 16/20] unwind_user/sframe: Add support for SFrame V3 flexible FDEs

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] Mismatch between SFrame V3 flexible FDE control word specification in the commit message and the actual implementation.
- [Low] The patch uses undefined macros `SFRAME_REG_SP` and `SFRAME_REG_FP` and includes a missing architecture header, breaking the build.
--

commit 82ce04f2a50a8ff116e0ca155714efff95332739
Author: Jens Remus <jremus@linux.ibm.com>

unwind_user/sframe: Add support for SFrame V3 flexible FDEs

This commit introduces support for SFrame V3 flexible FDEs, which encode CFA,
RA, and FP tracking information using FRE data words or padding words. It
adds logic to read flexible FDE control words and initialize the appropriate
CFA and rule data structures.

>     This enables the following flexible CFA and FP/RA recovery rules:
>     - CFA = register + offset       // reg_p=1, deref_p=0
>     - CFA = *(register + offset)    // reg_p=1, deref_p=1
>     - FP/RA = *(CFA + offset)       // reg_p=0, deref_p=0

[Severity: Medium]
Is this description in the commit message accurate?

The commit message states that the FP/RA rule uses reg_p=0, deref_p=0.
However, the implementation for this rule in __read_flex_fde_fre_datawords()
uses ra_ctl = 2, which corresponds to deref_p=1. 

Also, the commit message later notes that reg_p=0 and deref_p=0 is actually
an invalid padding word.

Could the commit message be updated to match the code's behavior to avoid
confusing future maintainers debugging the SFrame unwinder?

> diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
> index daa97d8b02316..b623dca072daa 100644
> --- a/kernel/unwind/sframe.c
> +++ b/kernel/unwind/sframe.c
> @@ -12,6 +12,7 @@
>  #include <linux/mm.h>
>  #include <linux/string_helpers.h>
>  #include <linux/sframe.h>
> +#include <asm/unwind_user_sframe.h>
>  #include <linux/unwind_user_types.h>

[Severity: Low]
Does this include break the build for intermediate commits?

This architecture header, along with the SFRAME_REG_SP and SFRAME_REG_FP
macros used later in this patch, do not appear to exist in the tree at this
commit.

Although this is fixed later in the patch series by the commit that enables
sframe unwinding on x86, missing headers and undefined macros break git
bisectability. 

Should these definitions be introduced in an earlier patch or within this
one so that this patch compiles cleanly?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260521142546.3908498-1-jremus@linux.ibm.com?part=16

Re: [PATCH v16 05/20] unwind_user/sframe: Add support for reading .sframe contents

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] Mixing unsafe_copy_from_user() and unsafe_get_user() inside a user_access_begin() block breaks user access state (PAN) on architectures like ARM64.
- [Low] Mixing goto-based cleanup with scoped_guard() in sframe_add_section() violates the kernel's cleanup subsystem rules.
--

Note: The standard inline-quoting format has been altered to a free-form
summary due to text recitation restrictions. Code snippets from the
original patch are omitted.

commit b0f7b5132f15107b2df84ba67a33ced97fd3372a
Author: Josh Poimboeuf <jpoimboe@kernel.org>
Subject: unwind_user/sframe: Add support for reading .sframe contents

This commit adds an sframe_find() interface to support unwinding user
space stacks using sframe information. It implements performant user space
access using user_read_access_begin() and unsafe accessors.

Link: https://lore.kernel.org/all/77c0d1ec143bf2a53d66c4ecb190e7e0a576fbfd.1737511963.git.jpoimboe@kernel.org/
Link: https://lore.kernel.org/all/b35ca3a3-8de5-4d32-8d30-d4e562f6b0de@linux.ibm.com/

[Severity: High]
In sframe_find(), scoped_user_read_access_size() opens a user access block.
Inside this block, __find_fde() uses unsafe_copy_from_user(), followed by
__find_fre() using unsafe_get_user() via UNSAFE_GET_USER_INC().

Does mixing these accessors risk breaking the user access state (PAN) on
architectures like ARM64?

On platforms that do not explicitly override unsafe_copy_from_user(), it
falls back to calling raw_copy_from_user(). With CONFIG_ARM64_SW_TTBR0_PAN
enabled, raw_copy_from_user() explicitly enables and then disables TTBR0,
re-enabling PAN during the copy. When it returns, user access is prematurely
disabled for the rest of the block.

Could the subsequent unsafe_get_user() in __find_fre() then trigger a fatal
page fault and kernel panic because TTBR0 is unmapped?

[Severity: Low]
In sframe_add_section(), scoped_guard(mmap_read_lock, mm) is used for
scope-based locking, but later the function uses goto err_free; to clean up
the allocated sec object on error paths.

This isn't a bug, but does this violate the cleanup subsystem guidelines?

The documentation for the cleanup subsystem states that functions should
convert all resources that need a goto cleanup to scope-based cleanup, or
convert none of them, specifically recommending against mixing goto-based
error handling and guard declarations in the same routine.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260521142546.3908498-1-jremus@linux.ibm.com?part=5

Re: [PATCH v16 10/20] unwind_user/sframe: Remove .sframe section on detected corruption

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] Concurrent removal of a corrupted or unmapped .sframe section triggers a user-controllable WARN_ON_ONCE.
- [High] Valid but paged-out .sframe sections are permanently removed due to transient page faults.
--

commit b574618cbc641ef52e2678be129e34a64bc4fb53
Author: Josh Poimboeuf <jpoimboe@kernel.org>

unwind_user/sframe: Remove .sframe section on detected corruption

To avoid continued attempted use of a bad .sframe section, this commit removes
it on demand when the first sign of corruption is detected.

> diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
> index 41ece3ca62a1f..e0eb2adf5a074 100644
> --- a/kernel/unwind/sframe.c
> +++ b/kernel/unwind/sframe.c

[ ... ]

> @@ -371,10 +371,15 @@ int sframe_find(unsigned long ip, struct unwind_user_frame *frame)
>  			ret = __find_fre(sec, &fde, ip, frame);
>  	}
>  
> +end:
> +	if (ret && ret != -ENOENT)
> +		WARN_ON_ONCE(sframe_remove_section(sec->sframe_start));

[Severity: High]
Can a concurrent unwind cause a user-controllable warning here?

If two threads concurrently fail to read a corrupted .sframe section, they 
could both reach this code. The first thread would successfully remove the 
section, but the second thread would fail to find it in the maple tree, 
causing sframe_remove_section() to return -EINVAL. 

This would trigger the WARN_ON_ONCE(), potentially allowing an unprivileged 
user to crash the system if panic_on_warn is enabled.

>  
>  	return ret;
>  
>  Efault:
> -	return -EFAULT;
> +	ret = -EFAULT;
> +	goto end;
>  }

[Severity: High]
Will this permanently remove perfectly valid .sframe sections if they happen 
to be paged out?

User space unwinding often happens in atomic contexts like perf NMIs where 
demand paging is not permitted. If a valid .sframe section is temporarily 
swapped out or hasn't been faulted in yet, the memory read operations will 
cleanly fail and jump here, setting ret to -EFAULT.

Since -EFAULT is not -ENOENT, the error handling logic jumps to the end label 
and treats this transient failure as permanent corruption, permanently removing 
the section from the maple tree. Applications might lose unwinding capabilities 
simply because their memory was temporarily paged out during a profiler sample.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260521142546.3908498-1-jremus@linux.ibm.com?part=10

Re: [PATCH v16 20/20] unwind_user/sframe: Add prctl() interface for registering .sframe sections

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 6 potential issue(s) to consider:

New issues:
- [High] The patch adds a test-only UAPI interface that is explicitly not intended for mainline inclusion, violating ABI stability rules.
- [High] Unbounded memory allocation in PR_ADD_SFRAME allows a local Denial of Service (DoS) via memory exhaustion.
- [Low] When SFrame support is disabled, the prctl options incorrectly return -ENOSYS instead of -EINVAL.

Pre-existing issues:
- [Critical] Improper handling of -EFAULT in sframe_find() leads to premature deletion of valid unwinding metadata and poses a severe NMI deadlock risk.
- [High] A malicious user application can reliably trigger a WARN_ON_ONCE in sframe_find() by causing concurrent removals of an .sframe section, potentially panicking the system.
- [High] Unbounded iteration in sframe_validate_section() without yielding the CPU can cause softlockup DoS.
--

commit f2ba64c060979156a7ef9c545cd667594369670a
Author: Josh Poimboeuf <jpoimboe@kernel.org>

unwind_user/sframe: Add prctl() interface for registering .sframe sections

The kernel doesn't have direct visibility to the ELF contents of shared
libraries. This commit adds prctl() interfaces to allow glibc to tell the
kernel where to find .sframe sections for unwinding.

> [
>   This adds an interface for prctl() for testing loading of sframes for
>   libraries. But this interface should really be a system call. This patch
>   is for testing purposes only and should not be applied to mainline.
> ]

[Severity: High]
Since this is explicitly marked as a temporary test patch, should it be
redesigned as a proper system call or removed before being merged?

Adding temporary or experimental prctl() interfaces exposes a temporary ABI to
userspace which must be maintained indefinitely, polluting the UAPI.

> diff --git a/kernel/sys.c b/kernel/sys.c
> index 62e842055cc9c..b0a9b1e3ccd7c 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c

[ ... ]

> @@ -2907,6 +2908,14 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>  		if (arg3 & PR_CFI_LOCK && !(arg3 & PR_CFI_DISABLE))
>  			error = arch_prctl_lock_branch_landing_pad_state(me);
>  		break;
> +	case PR_ADD_SFRAME:
> +		error = sframe_add_section(arg2, arg3, arg4, arg5);

[Severity: High]
Could this allow a local Denial of Service via memory exhaustion?

A user process can repeatedly call prctl(PR_ADD_SFRAME) with valid, small
ranges. If each call allocates a new struct sframe_section and inserts it
into the mm->sframe_mt maple tree using GFP_KERNEL_ACCOUNT, an unprivileged
user might exhaust kernel memory since there is no upper limit on the total
number of sections a process can register.

[Severity: Low]
Is it intentional that the fallback stub for sframe_add_section() returns
-ENOSYS when SFrame support is disabled?

include/linux/sframe.h:sframe_add_section() {
    ...
    return -ENOSYS;
}

Standard kernel conventions dictate that unsupported or disabled prctl options
should return -EINVAL. Returning -ENOSYS incorrectly indicates to userspace
that the entire prctl syscall is unimplemented.

[Severity: High]
This is a pre-existing issue, but is there a risk of a softlockup Denial of
Service during section validation?

When registering a new .sframe section via PR_ADD_SFRAME, the kernel
synchronously validates all FDE and FRE entries in sframe_validate_section().
Because the number of FDEs is read from user-space memory and can be extremely
large, an attacker could provide a massive amount of FDEs/FREs.

Since the validation loop does not contain cond_resched(), the kernel could
spin here for seconds without yielding, triggering the softlockup detector.

> +		break;
> +	case PR_REMOVE_SFRAME:
> +		if (arg3 || arg4 || arg5)
> +			return -EINVAL;
> +		error = sframe_remove_section(arg2);

[Severity: Critical]
This is a pre-existing issue, but does handling -EFAULT in sframe_find() risk
a severe NMI deadlock and premature deletion of valid metadata?

If unsafe_get_user() cleanly faults because the memory is temporarily paged
out, it sets ret = -EFAULT. The cleanup block then calls
WARN_ON_ONCE(sframe_remove_section(sec->sframe_start)).

Because sframe_find() is used by stack unwinders (like perf) that execute
in NMI context, triggering sframe_remove_section() inside an NMI attempts
to acquire the maple tree's internal spinlock (mt_lock). If the NMI
interrupted a thread already holding mt_lock, this could result in a hard
deadlock. Furthermore, this permanently destroys perfectly valid unwinding
metadata simply because a page was not resident.

[Severity: High]
This is a pre-existing issue, but might a malicious application reliably
trigger the WARN_ON_ONCE in sframe_find(), potentially panicking the system?

If an .sframe section returns -EFAULT because it is paged out, the error
path calls WARN_ON_ONCE(sframe_remove_section(sec->sframe_start)).
If sframe_remove_section() fails to find the section, it returns -EINVAL,
causing the warning to fire.

This condition could be reliably triggered if multiple threads concurrently
unwind through the same paged-out section, or if one thread unwinds while
another explicitly removes the section using the newly added
prctl(PR_REMOVE_SFRAME). If panic_on_warn is enabled, this might allow
unprivileged users to reliably crash the system.

> +		break;
>  	default:
>  		trace_task_prctl_unknown(option, arg2, arg3, arg4, arg5);
>  		error = -EINVAL;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260521142546.3908498-1-jremus@linux.ibm.com?part=20

Re: [PATCH v16 18/20] unwind_user/sframe: Duplicate registered .sframe section data on clone/fork

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:

New issues:
- [Critical] Use-After-Free of maple tree nodes due to lockless traversal without RCU protection.
- [Medium] Mixing goto-based error handling with guard() in the same function.

Pre-existing issues:
- [High] Spinlock deadlock due to calling `mtree_erase` from NMI/interrupt context.
--

commit dd76a8e2b70424efa3c49c5cac126edfd3a77425
Author: Jens Remus <jremus@linux.ibm.com>

unwind_user/sframe: Duplicate registered .sframe section data on clone/fork
    
When duplicating a process' virtual memory mappings also duplicate all
of its registered .sframe sections stored in the per-mm maple tree to
enable stacktracing using sframe of the child process.

> diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
> index 7f439600b0f0a..db88d993dff1f 100644
> --- a/kernel/unwind/sframe.c
> +++ b/kernel/unwind/sframe.c

[ ... ]

> @@ -875,6 +875,54 @@ int sframe_remove_section(unsigned long sframe_start)
> +int sframe_dup_mm(struct mm_struct *mm, struct mm_struct *oldmm)
> +{
> +	struct sframe_section *sec, *oldsec;
> +	unsigned long index = 0;
> +	int ret;
> +
> +	guard(srcu)(&sframe_srcu);
> +
> +	mt_for_each(&oldmm->sframe_mt, oldsec, index, ULONG_MAX) {

[Severity: Critical]
Does this lockless iteration risk a use-after-free on maple tree nodes?

The maple tree is initialized via INIT_MM_SFRAME as MTREE_INIT(sframe_mt,
0), which omits the MT_FLAGS_USE_RCU flag. Without this flag, tree
modifications free internal tree nodes synchronously via kfree() instead
of call_rcu().

If sframe_remove_section() modifies the tree concurrently, could this
lockless mt_for_each() access freed maple tree nodes?

[Severity: High]
This isn't a bug introduced by this patch, but looking at how the maple
tree is used here and in sframe_remove_section(), is there a deadlock
risk if sframe_remove_section() is called from NMI/interrupt context?

Since stack unwinding can occur asynchronously in NMI or hardirq context
(e.g., via perf_callchain_user), if it detects a corrupted section and
triggers sframe_remove_section() which ultimately calls mtree_erase(),
that will take a non-IRQ-safe spin_lock via mtree_lock(mt).

If an NMI interrupts a thread that is already holding the mtree_lock
(for instance, during sframe_add_section), could this instantly
hard-deadlock?

> +		sec = kzalloc(sizeof(*sec), GFP_KERNEL_ACCOUNT);
> +		if (!sec)
> +			return -ENOMEM;
> +
> +		__sframe_dup_section(sec, oldsec);
> +
> +		ret = mtree_insert_range(&mm->sframe_mt,
> +					 sec->text_start,
> +					 sec->text_end - 1,
> +					 sec, GFP_KERNEL_ACCOUNT);
> +		if (ret)
> +			goto err_free;
> +	}
> +
> +	return 0;
> +
> +err_free:

[Severity: Medium]
Are we mixing goto-based error handling and scope-based cleanups in the
same function?

This function declares guard(srcu)(&sframe_srcu) at the top, but then
uses a goto-based cleanup label here. According to the cleanup subsystem
guidelines in include/linux/cleanup.h, mixing goto and scope-based
cleanup helpers in the same function creates confusing ownership
semantics.

Should this function either convert all resources to scope-based cleanup,
or convert none of them?

> +	free_section(sec);
> +	return ret;
> +}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260521142546.3908498-1-jremus@linux.ibm.com?part=18

Re: [PATCH v16 05/20] unwind_user/sframe: Add support for reading .sframe contents

[Jens Remus]

On 5/21/2026 5:18 PM, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
> - [High] Mixing unsafe_copy_from_user() and unsafe_get_user() inside a user_access_begin() block breaks user access state (PAN) on architectures like ARM64.
> - [Low] Mixing goto-based cleanup with scoped_guard() in sframe_add_section() violates the kernel's cleanup subsystem rules.
> --
> 
> Note: The standard inline-quoting format has been altered to a free-form
> summary due to text recitation restrictions. Code snippets from the
> original patch are omitted.
> 
> commit b0f7b5132f15107b2df84ba67a33ced97fd3372a
> Author: Josh Poimboeuf <jpoimboe@kernel.org>
> Subject: unwind_user/sframe: Add support for reading .sframe contents
> 
> This commit adds an sframe_find() interface to support unwinding user
> space stacks using sframe information. It implements performant user space
> access using user_read_access_begin() and unsafe accessors.
> 
> Link: https://lore.kernel.org/all/77c0d1ec143bf2a53d66c4ecb190e7e0a576fbfd.1737511963.git.jpoimboe@kernel.org/
> Link: https://lore.kernel.org/all/b35ca3a3-8de5-4d32-8d30-d4e562f6b0de@linux.ibm.com/
> 
> [Severity: High]
> In sframe_find(), scoped_user_read_access_size() opens a user access block.
> Inside this block, __find_fde() uses unsafe_copy_from_user(), followed by
> __find_fre() using unsafe_get_user() via UNSAFE_GET_USER_INC().

Previously (see v15) the code was using user_read_access_begin() and
user_read_access_end().  IIUC scoped_user_read_access_size() is just
another mean to express the same and it behaves the same.  So if the
issue brought up by Sashiko AI review is valid, then it would also
exist with the previous implementation.

> 
> Does mixing these accessors risk breaking the user access state (PAN) on
> architectures like ARM64?
> 
> On platforms that do not explicitly override unsafe_copy_from_user(), it
> falls back to calling raw_copy_from_user(). With CONFIG_ARM64_SW_TTBR0_PAN
> enabled, raw_copy_from_user() explicitly enables and then disables TTBR0,
> re-enabling PAN during the copy. When it returns, user access is prematurely
> disabled for the rest of the block.
> 
> Could the subsequent unsafe_get_user() in __find_fre() then trigger a fatal
> page fault and kernel panic because TTBR0 is unmapped?

If that would be true, wouldn't then the arm64 raw_copy_from_user() or
the common unsafe_copy_from_user() implementation be broken?

Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
jremus@de.ibm.com / jremus@linux.ibm.com

IBM Deutschland Research & Development GmbH; Vorsitzender des Aufsichtsrats: Wolfgang Wendt; Geschäftsführung: David Faller; Sitz der Gesellschaft: Ehningen; Registergericht: Amtsgericht Stuttgart, HRB 243294
IBM Data Privacy Statement: https://www.ibm.com/privacy/

Re: [PATCH v16 07/20] unwind_user/sframe: Wire up unwind_user to sframe

[Jens Remus]

On 5/21/2026 4:53 PM, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] Missing instruction pointer adjustment for return addresses during SFrame unwinding of non-topmost frames.
> --
> 
> commit 9e76c3f974e7ef0d88d0ca8c60fa84ef664ebee7
> Author: Josh Poimboeuf <jpoimboe@kernel.org>
> 
> unwind_user/sframe: Wire up unwind_user to sframe
> 
> Now that the sframe infrastructure is fully in place, make it work by hooking
> it up to the unwind_user interface.
> 
>> diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
>> index 90ab3c1a205ef..1fb2724197332 100644
>> --- a/kernel/unwind/user.c
>> +++ b/kernel/unwind/user.c
> 
> [ ... ]
> 
>> @@ -82,6 +83,16 @@ static int unwind_user_next_fp(struct unwind_user_state *state)
>>  	return unwind_user_next_common(state, &fp_frame);
>>  }
>>  
>> +static int unwind_user_next_sframe(struct unwind_user_state *state)
>> +{
>> +	struct unwind_user_frame frame;
>> +
>> +	/* sframe expects the frame to be local storage */
>> +	if (sframe_find(state->ip, &frame))
> 
> [Severity: Medium]
> For non-topmost stack frames, state->ip holds the return address, which points
> to the instruction after the call. If a call is the very last instruction of a
> function (like a call to a noreturn function), the return address will point to
> the first instruction of the next contiguous function in memory.
> 
> Could sframe_find() incorrectly match the next function's FDE and apply its
> unwind rules to the current frame? Other table-driven unwinders handle this
> by subtracting 1 from the instruction pointer for non-topmost frames.

Valid.  Every now and then during testing on s390 a stacktrace ends e.g.
as follows, because the return address of a function with
__attribute__((noreturn)), such as exit(), might point at the following
function in storage, which then confuses unwind user:

objdump    1060    26.324199:     100010 task-clock:ppp:
             3ff9ec908b4 dfs_traversal.part.0+0x34 (/usr/lib/ld64.so.1)
             3ff9ec90900 dfs_traversal.part.0+0x80 (/usr/lib/ld64.so.1)
             3ff9ec90e68 _dl_sort_maps+0x4b8 (/usr/lib/ld64.so.1)
             3ff9ec84aa2 _dl_fini+0x252 (/usr/lib/ld64.so.1)
             3ff9e856b06 __run_exit_handlers+0x176 (/usr/lib64/libc.so.6)
             3ff9e856c00 internal_addseverity+0x0 (/usr/lib64/libc.so.6)

$ objdump -d build-sframe/libc.so
...
000000000004dee0 <exit>:
   4dee0:       eb ef f0 70 00 24       stmg    %r14,%r15,112(%r15)
   4dee6:       a7 59 00 01             lghi    %r5,1
   4deea:       e3 f0 ff 60 ff 71       lay     %r15,-160(%r15)
   4def0:       a7 49 00 01             lghi    %r4,1
   4def4:       c0 30 00 0d 9b a2       larl    %r3,201638 <__exit_funcs>
   4defa:       c0 e5 ff ff fe 9b       brasl   %r14,4dc30 <__run_exit_handlers>

000000000004df00 <internal_addseverity>:
   4df00:       eb 9f f0 48 00 24       stmg    %r9,%r15,72(%r15)
   4df06:       c0 10 00 0d 9b 9d       larl    %r1,201640 <severity_list>
   4df0c:       e3 f0 ff 60 ff 71       lay     %r15,-160(%r15)
...

But this should then be addressed in unwind_user_next_common(), which
would simply need to determine the next IP as RA - 1.  I have not
addressed this yet, as signal frames might require different handling.

> 
>> +		return -ENOENT;
>> +	return unwind_user_next_common(state, &frame);
>> +}
> 

Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
jremus@de.ibm.com / jremus@linux.ibm.com

IBM Deutschland Research & Development GmbH; Vorsitzender des Aufsichtsrats: Wolfgang Wendt; Geschäftsführung: David Faller; Sitz der Gesellschaft: Ehningen; Registergericht: Amtsgericht Stuttgart, HRB 243294
IBM Data Privacy Statement: https://www.ibm.com/privacy/

Re: [PATCH v16 11/20] unwind_user/sframe: Show file name in debug output

[Jens Remus]

On 5/21/2026 5:05 PM, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
> 
> New issues:
> - [Low] VMA Classification Bug in `dbg_init()`

Will be addressed in next version as suggested by Steven during v15
review:

https://lore.kernel.org/all/20260521122033.4648359e@gandalf.local.home/

Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
jremus@de.ibm.com / jremus@linux.ibm.com

IBM Deutschland Research & Development GmbH; Vorsitzender des Aufsichtsrats: Wolfgang Wendt; Geschäftsführung: David Faller; Sitz der Gesellschaft: Ehningen; Registergericht: Amtsgericht Stuttgart, HRB 243294
IBM Data Privacy Statement: https://www.ibm.com/privacy/

Re: [PATCH v16 10/20] unwind_user/sframe: Remove .sframe section on detected corruption

[Jens Remus]

On 5/21/2026 5:19 PM, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
> - [High] Concurrent removal of a corrupted or unmapped .sframe section triggers a user-controllable WARN_ON_ONCE.
> - [High] Valid but paged-out .sframe sections are permanently removed due to transient page faults.
> --
> 
> commit b574618cbc641ef52e2678be129e34a64bc4fb53
> Author: Josh Poimboeuf <jpoimboe@kernel.org>
> 
> unwind_user/sframe: Remove .sframe section on detected corruption
> 
> To avoid continued attempted use of a bad .sframe section, this commit removes
> it on demand when the first sign of corruption is detected.
> 
>> diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
>> index 41ece3ca62a1f..e0eb2adf5a074 100644
>> --- a/kernel/unwind/sframe.c
>> +++ b/kernel/unwind/sframe.c
> 
> [ ... ]
> 
>> @@ -371,10 +371,15 @@ int sframe_find(unsigned long ip, struct unwind_user_frame *frame)
>>  			ret = __find_fre(sec, &fde, ip, frame);
>>  	}
>>  
>> +end:
>> +	if (ret && ret != -ENOENT)
>> +		WARN_ON_ONCE(sframe_remove_section(sec->sframe_start));
> 
> [Severity: High]
> Can a concurrent unwind cause a user-controllable warning here?
> 
> If two threads concurrently fail to read a corrupted .sframe section, they 
> could both reach this code. The first thread would successfully remove the 
> section, but the second thread would fail to find it in the maple tree, 
> causing sframe_remove_section() to return -EINVAL. 
> 
> This would trigger the WARN_ON_ONCE(), potentially allowing an unprivileged 
> user to crash the system if panic_on_warn is enabled.

This seems valid and therefore I think we should remove the WARN_ON_ONCE().

Any objections?

> 
>>  
>>  	return ret;
>>  
>>  Efault:
>> -	return -EFAULT;
>> +	ret = -EFAULT;
>> +	goto end;
>>  }
> 
> [Severity: High]
> Will this permanently remove perfectly valid .sframe sections if they happen 
> to be paged out?
> 
> User space unwinding often happens in atomic contexts like perf NMIs where 
> demand paging is not permitted. If a valid .sframe section is temporarily 
> swapped out or hasn't been faulted in yet, the memory read operations will 
> cleanly fail and jump here, setting ret to -EFAULT.
> 
> Since -EFAULT is not -ENOENT, the error handling logic jumps to the end label 
> and treats this transient failure as permanent corruption, permanently removing 
> the section from the maple tree. Applications might lose unwinding capabilities 
> simply because their memory was temporarily paged out during a profiler sample.

No.  IIUC the deferred stacktracing explicitly allows for page faults to
be handled.  So any page faults during reading of .sframe section data
from user space should not cause an -EFAULT and thus never erroneous
removal of valid .sframe.

Thanks and regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
jremus@de.ibm.com / jremus@linux.ibm.com

IBM Deutschland Research & Development GmbH; Vorsitzender des Aufsichtsrats: Wolfgang Wendt; Geschäftsführung: David Faller; Sitz der Gesellschaft: Ehningen; Registergericht: Amtsgericht Stuttgart, HRB 243294
IBM Data Privacy Statement: https://www.ibm.com/privacy/

Re: [PATCH v16 12/20] unwind_user/sframe: Add .sframe validation option

[Jens Remus]

On 5/21/2026 5:02 PM, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] The `.sframe` validation loop in `sframe_validate_section` lacks `cond_resched()`, allowing maliciously large or crafted `.sframe` sections to cause CPU soft lockups.

cond_resched() is not required according to v14 review feedback from
Steven.

Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
jremus@de.ibm.com / jremus@linux.ibm.com

IBM Deutschland Research & Development GmbH; Vorsitzender des Aufsichtsrats: Wolfgang Wendt; Geschäftsführung: David Faller; Sitz der Gesellschaft: Ehningen; Registergericht: Amtsgericht Stuttgart, HRB 243294
IBM Data Privacy Statement: https://www.ibm.com/privacy/

Re: [PATCH v16 02/20] unwind_user/sframe: Add support for reading .sframe headers

[Jens Remus]

On 5/21/2026 4:51 PM, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] Calculations for sframe section boundaries lack overflow checks, allowing malformed headers to bypass bounds validation on 32-bit architectures.

SFrame only supports 64-bit architectures.  A BUILD_BUG_ON() is
introduced in "[PATCH v16 05/20] unwind_user/sframe: Add support
for reading .sframe contents".

I might move that to this patch in the next version to silence
this.

Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
jremus@de.ibm.com / jremus@linux.ibm.com

IBM Deutschland Research & Development GmbH; Vorsitzender des Aufsichtsrats: Wolfgang Wendt; Geschäftsführung: David Faller; Sitz der Gesellschaft: Ehningen; Registergericht: Amtsgericht Stuttgart, HRB 243294
IBM Data Privacy Statement: https://www.ibm.com/privacy/

Re: [PATCH v16 08/20] unwind_user: Stop when reaching an outermost frame

[Jens Remus]

On 5/21/2026 4:47 PM, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] The newly added `outermost` field in `struct unwind_user_frame` is left uninitialized in `unwind_user_next_sframe()`, causing `unwind_user_next_common()` to read stack garbage and potentially terminate unwinding prematurely.

Ignore: This is no longer an issue after subsequent "[PATCH v16 09/20]
unwind_user/sframe: Add support for outermost frame indication".

Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
jremus@de.ibm.com / jremus@linux.ibm.com

IBM Deutschland Research & Development GmbH; Vorsitzender des Aufsichtsrats: Wolfgang Wendt; Geschäftsführung: David Faller; Sitz der Gesellschaft: Ehningen; Registergericht: Amtsgericht Stuttgart, HRB 243294
IBM Data Privacy Statement: https://www.ibm.com/privacy/

Re: [PATCH v16 16/20] unwind_user/sframe: Add support for SFrame V3 flexible FDEs

[Jens Remus]

On 5/21/2026 5:14 PM, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
> - [Medium] Mismatch between SFrame V3 flexible FDE control word specification in the commit message and the actual implementation.
> - [Low] The patch uses undefined macros `SFRAME_REG_SP` and `SFRAME_REG_FP` and includes a missing architecture header, breaking the build.
> --
> 
> commit 82ce04f2a50a8ff116e0ca155714efff95332739
> Author: Jens Remus <jremus@linux.ibm.com>
> 
> unwind_user/sframe: Add support for SFrame V3 flexible FDEs
> 
> This commit introduces support for SFrame V3 flexible FDEs, which encode CFA,
> RA, and FP tracking information using FRE data words or padding words. It
> adds logic to read flexible FDE control words and initialize the appropriate
> CFA and rule data structures.
> 
>>     This enables the following flexible CFA and FP/RA recovery rules:
>>     - CFA = register + offset       // reg_p=1, deref_p=0
>>     - CFA = *(register + offset)    // reg_p=1, deref_p=1
>>     - FP/RA = *(CFA + offset)       // reg_p=0, deref_p=0
> 
> [Severity: Medium]
> Is this description in the commit message accurate?
> 
> The commit message states that the FP/RA rule uses reg_p=0, deref_p=0.
> However, the implementation for this rule in __read_flex_fde_fre_datawords()
> uses ra_ctl = 2, which corresponds to deref_p=1. 

My bad!  Will correct the commit message in the next version.

> 
> Also, the commit message later notes that reg_p=0 and deref_p=0 is actually
> an invalid padding word.
> 
> Could the commit message be updated to match the code's behavior to avoid
> confusing future maintainers debugging the SFrame unwinder?
> 
>> diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
>> index daa97d8b02316..b623dca072daa 100644
>> --- a/kernel/unwind/sframe.c
>> +++ b/kernel/unwind/sframe.c
>> @@ -12,6 +12,7 @@
>>  #include <linux/mm.h>
>>  #include <linux/string_helpers.h>
>>  #include <linux/sframe.h>
>> +#include <asm/unwind_user_sframe.h>
>>  #include <linux/unwind_user_types.h>
> 
> [Severity: Low]
> Does this include break the build for intermediate commits?
> 
> This architecture header, along with the SFRAME_REG_SP and SFRAME_REG_FP
> macros used later in this patch, do not appear to exist in the tree at this
> commit.

This is intended.  kernel/unwind/sframe.o is only built if an arch
enables HAVE_UNWIND_USER_SFRAME and provides an arch-specific
asm/unwind_user_sframe.h header that defines at least SFRAME_REG_SP and
SFRAME_REG_FP.

> 
> Although this is fixed later in the patch series by the commit that enables
> sframe unwinding on x86, missing headers and undefined macros break git
> bisectability. 
> 
> Should these definitions be introduced in an earlier patch or within this
> one so that this patch compiles cleanly?
> 

Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
jremus@de.ibm.com / jremus@linux.ibm.com

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Re: [PATCH v16 05/20] unwind_user/sframe: Add support for reading .sframe contents

[Steven Rostedt]

On Fri, 22 May 2026 11:26:00 +0200
Jens Remus <jremus@linux.ibm.com> wrote:

> Previously (see v15) the code was using user_read_access_begin() and
> user_read_access_end().  IIUC scoped_user_read_access_size() is just
> another mean to express the same and it behaves the same.  So if the
> issue brought up by Sashiko AI review is valid, then it would also
> exist with the previous implementation.

Note, Sashiko's reviews are statistical, which means you can get
different issues brought up by running it twice on the same code.

-- Steve

Re: [PATCH v16 02/20] unwind_user/sframe: Add support for reading .sframe headers

[Steven Rostedt]

On Thu, 21 May 2026 16:25:28 +0200
Jens Remus <jremus@linux.ibm.com> wrote:

> +static int sframe_read_header(struct sframe_section *sec)
> +{
> +	unsigned long header_end, fdes_start, fdes_end, fres_start, fres_end;
> +	struct sframe_header shdr;
> +	unsigned int num_fdes;
> +
> +	if (copy_from_user(&shdr, (void __user *)sec->sframe_start, sizeof(shdr))) {
> +		dbg("header usercopy failed\n");
> +		return -EFAULT;
> +	}
> +
> +	if (shdr.preamble.magic != SFRAME_MAGIC ||
> +	    shdr.preamble.version != SFRAME_VERSION_3 ||
> +	    !(shdr.preamble.flags & SFRAME_F_FDE_SORTED) ||
> +	    !(shdr.preamble.flags & SFRAME_F_FDE_FUNC_START_PCREL) ||
> +	    shdr.auxhdr_len) {
> +		dbg("bad/unsupported sframe header\n");
> +		return -EINVAL;
> +	}
> +
> +	if (!shdr.num_fdes || !shdr.num_fres) {
> +		dbg("no fde/fre entries\n");
> +		return -EINVAL;
> +	}
> +
> +	header_end = sec->sframe_start + SFRAME_HEADER_SIZE(shdr);
> +	if (header_end >= sec->sframe_end) {
> +		dbg("header doesn't fit in section\n");
> +		return -EINVAL;
> +	}
> +
> +	num_fdes   = shdr.num_fdes;
> +	fdes_start = header_end + shdr.fdes_off;
> +	fdes_end   = fdes_start + (num_fdes * sizeof(struct sframe_fde_v3));
> +
> +	fres_start = header_end + shdr.fres_off;
> +	fres_end   = fres_start + shdr.fre_len;
> +
> +	if (fres_start < fdes_end || fres_end > sec->sframe_end) {
> +		dbg("inconsistent fde/fre offsets\n");
> +		return -EINVAL;
> +	}

I really think we should also test if fres_start >= fres_end. Because
if fres_start is near sec->sframe_end and on 32bit archs fre_len makes
fres_end overflow, this doesn't catch it.

Even if it doesn't cause issues later, I rather have it caught here.

-- Steve

> +
> +	sec->num_fdes		= num_fdes;
> +	sec->fdes_start		= fdes_start;
> +	sec->fres_start		= fres_start;
> +	sec->fres_end		= fres_end;
> +
> +	sec->ra_off		= shdr.cfa_fixed_ra_offset;
> +	sec->fp_off		= shdr.cfa_fixed_fp_offset;
> +
> +	return 0;
> +}

Re: [PATCH v16 03/20] unwind_user/sframe: Store .sframe section data in per-mm maple tree

[Steven Rostedt]

On Thu, 21 May 2026 16:25:29 +0200
Jens Remus <jremus@linux.ibm.com> wrote:

>  int sframe_remove_section(unsigned long sframe_start)
>  {
> -	return -ENOSYS;
> +	struct mm_struct *mm = current->mm;
> +	struct sframe_section *sec;
> +	unsigned long index = 0;
> +	bool found = false;
> +	int ret = 0;
> +
> +	guard(srcu)(&sframe_srcu);
> +
> +	mt_for_each(&mm->sframe_mt, sec, index, ULONG_MAX) {
> +		if (sec->sframe_start == sframe_start) {
> +			found = true;
> +			ret |= __sframe_remove_section(mm, sec);

Because this is all internal data, the __sframe_remove_section() should
never fail. Perhaps we should add a WARN_ON() if it does?

		if (sec->sframe_start == sframe_start) {
			ret |= __sframe_remove_section(mm, sec);
			WARN_ON(!found && ret);
			found = true;

-- Steve



> +		}
> +	}
> +
> +	if (!found || ret)
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +