[PATCH v14 02/19] unwind_user/sframe: Add support for reading .sframe headers

[Jens Remus <jremus@linux.ibm.com>]

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 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 8e71c6e7a68a..24d1fe93ff4a 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -27864,6 +27864,7 @@ 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..c128c1eeaca2
--- /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("zero-length 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);
+	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