* [PATCH v5 1/7] riscv: stacktrace: Add frame record metadata
2026-08-04 10:36 [PATCH v5 0/7] riscv: Add reliable stack unwinding for livepatch Wang Han
@ 2026-08-04 10:36 ` Wang Han
2026-08-04 10:36 ` [PATCH v5 2/7] riscv: stacktrace: disable KASAN and KCOV instrumentation for stacktrace.o Wang Han
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: Wang Han @ 2026-08-04 10:36 UTC (permalink / raw)
To: Paul Walmsley, Palmer Dabbelt, Albert Ou
Cc: Alexandre Ghiti, linux-riscv, Oleg Nesterov, Steven Rostedt,
Masami Hiramatsu, Mark Rutland, Peter Zijlstra, Ingo Molnar,
Arnaldo Carvalho de Melo, Namhyung Kim, Alexander Shishkin,
Jiri Olsa, Ian Rogers, Adrian Hunter, James Clark, Josh Poimboeuf,
Jiri Kosina, Miroslav Benes, Petr Mladek, Joe Lawrence,
Shuah Khan, oliver.yang, xueshuai, zhuo.song, jkchen,
Marcos Paulo de Souza, linux-kernel, linux-trace-kernel,
linux-perf-users, live-patching, linux-kselftest
Reliable frame-pointer unwinding needs an explicit way to identify
exception boundaries and the final entry frame. The existing unwinder
infers those boundaries from return addresses, which is too loose for a
future reliable unwinder.
Add a small metadata frame record to pt_regs and initialize it on
exception entry, kernel stack overflow, kernel thread fork, user fork,
and early idle task setup. The record uses a zero {fp, ra} sentinel plus
a type field so a later unwinder can distinguish a final user-to-kernel
boundary from a nested kernel pt_regs boundary.
This follows the arm64 metadata frame-record model, adapted to the
RISC-V {fp, ra} frame record convention.
The metadata is established at the RISC-V entry boundaries that need an
explicit unwind marker:
* exception entry clears the metadata {fp, ra} pair and uses SPP
(or MPP in M-mode) to record whether the pt_regs frame is the final
user-to-kernel boundary or a nested kernel boundary;
* the kernel stack overflow path builds a nested pt_regs metadata
record on the overflow stack so an unwinder can resume from the
pre-overflow s0 saved in PT_S0;
* _start_kernel builds the init task's final metadata record, while
the secondary CPU path sets up s0 before smp_callin() so idle-task
unwinding does not inherit an undefined caller frame;
* copy_thread creates matching final metadata records for new kernel
and user tasks, and keeps s0 available for the frame-pointer chain.
Keep the embedded metadata-record field offsets distinct from the
s0-relative STACKFRAME_* offsets used by call_on_irq_stack(), because
the latter describe a frame record relative to s0 rather than to the
record base.
These changes keep s0 reserved for the frame-pointer chain at task and
exception boundaries.
Reviewed-by: Shuai Xue <xueshuai@linux.alibaba.com>
Signed-off-by: Wang Han <wanghan@linux.alibaba.com>
---
arch/riscv/include/asm/ptrace.h | 9 ++++
arch/riscv/include/asm/stacktrace/frame.h | 53 +++++++++++++++++++++++
arch/riscv/kernel/asm-offsets.c | 6 +++
arch/riscv/kernel/entry.S | 39 ++++++++++++++++-
arch/riscv/kernel/head.S | 23 ++++++++++
arch/riscv/kernel/process.c | 33 +++++++++++++-
6 files changed, 159 insertions(+), 4 deletions(-)
create mode 100644 arch/riscv/include/asm/stacktrace/frame.h
diff --git a/arch/riscv/include/asm/ptrace.h b/arch/riscv/include/asm/ptrace.h
index addc8188152f..4b9b0f279214 100644
--- a/arch/riscv/include/asm/ptrace.h
+++ b/arch/riscv/include/asm/ptrace.h
@@ -8,6 +8,7 @@
#include <uapi/asm/ptrace.h>
#include <asm/csr.h>
+#include <asm/stacktrace/frame.h>
#include <linux/compiler.h>
#ifndef __ASSEMBLER__
@@ -53,6 +54,14 @@ struct pt_regs {
unsigned long cause;
/* a0 value before the syscall */
unsigned long orig_a0;
+
+ /*
+ * This frame record is entirely zeroed on exception entry, allowing the
+ * unwinder to identify exception boundaries. The type field encodes
+ * whether the exception was taken from user (FINAL) or kernel (PT_REGS)
+ * mode.
+ */
+ struct frame_record_meta stackframe;
};
#define PTRACE_SYSEMU 0x1f
diff --git a/arch/riscv/include/asm/stacktrace/frame.h b/arch/riscv/include/asm/stacktrace/frame.h
new file mode 100644
index 000000000000..5720a6c65fe8
--- /dev/null
+++ b/arch/riscv/include/asm/stacktrace/frame.h
@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef __ASM_RISCV_STACKTRACE_FRAME_H
+#define __ASM_RISCV_STACKTRACE_FRAME_H
+
+/*
+ * See: arch/arm64/include/asm/stacktrace/frame.h for the reference
+ * implementation.
+ */
+
+/*
+ * - FRAME_META_TYPE_NONE
+ *
+ * This value is reserved.
+ *
+ * - FRAME_META_TYPE_FINAL
+ *
+ * The record is the last entry on the stack.
+ * Unwinding should terminate successfully.
+ *
+ * - FRAME_META_TYPE_PT_REGS
+ *
+ * The record is embedded within a struct pt_regs, recording the registers at
+ * an arbitrary point in time.
+ * Unwinding should consume pt_regs::epc, followed by pt_regs::ra.
+ *
+ * Note: all other values are reserved and should result in unwinding
+ * terminating with an error.
+ */
+#define FRAME_META_TYPE_NONE 0
+#define FRAME_META_TYPE_FINAL 1
+#define FRAME_META_TYPE_PT_REGS 2
+
+#ifndef __ASSEMBLER__
+/*
+ * A standard RISC-V frame record.
+ */
+struct frame_record {
+ unsigned long fp;
+ unsigned long ra;
+};
+
+/*
+ * A metadata frame record indicating a special unwind.
+ * The record::{fp,ra} fields must be zero to indicate the presence of
+ * metadata.
+ */
+struct frame_record_meta {
+ struct frame_record record;
+ unsigned long type;
+};
+#endif /* __ASSEMBLER__ */
+
+#endif /* __ASM_RISCV_STACKTRACE_FRAME_H */
diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
index a75f0cfea1e9..d0eaf2c902fb 100644
--- a/arch/riscv/kernel/asm-offsets.c
+++ b/arch/riscv/kernel/asm-offsets.c
@@ -131,6 +131,9 @@ void asm_offsets(void)
OFFSET(PT_BADADDR, pt_regs, badaddr);
OFFSET(PT_CAUSE, pt_regs, cause);
+ DEFINE(S_STACKFRAME, offsetof(struct pt_regs, stackframe));
+ DEFINE(S_STACKFRAME_TYPE, offsetof(struct pt_regs, stackframe.type));
+
OFFSET(SUSPEND_CONTEXT_REGS, suspend_context, regs);
OFFSET(HIBERN_PBE_ADDR, pbe, address);
@@ -503,6 +506,9 @@ void asm_offsets(void)
DEFINE(STACKFRAME_SIZE_ON_STACK, ALIGN(sizeof(struct stackframe), STACK_ALIGN));
DEFINE(STACKFRAME_FP, offsetof(struct stackframe, fp) - sizeof(struct stackframe));
DEFINE(STACKFRAME_RA, offsetof(struct stackframe, ra) - sizeof(struct stackframe));
+ DEFINE(STACKFRAME_RECORD_SIZE, sizeof(struct frame_record));
+ OFFSET(FRAME_RECORD_FP, frame_record, fp);
+ OFFSET(FRAME_RECORD_RA, frame_record, ra);
#ifdef CONFIG_FUNCTION_TRACER
DEFINE(FTRACE_OPS_FUNC, offsetof(struct ftrace_ops, func));
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index d799c4e56f80..588d5bbe74f5 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -11,6 +11,7 @@
#include <asm/asm.h>
#include <asm/csr.h>
#include <asm/scs.h>
+#include <asm/stacktrace/frame.h>
#include <asm/unistd.h>
#include <asm/page.h>
#include <asm/thread_info.h>
@@ -198,6 +199,27 @@ SYM_CODE_START(handle_exception)
REG_S s4, PT_CAUSE(sp)
REG_S s5, PT_TP(sp)
+ /*
+ * Create a metadata frame record. The unwinder will use this to
+ * identify and unwind exception boundaries.
+ */
+ REG_S zero, (S_STACKFRAME + FRAME_RECORD_FP)(sp) /* stackframe.record.fp = 0 */
+ REG_S zero, (S_STACKFRAME + FRAME_RECORD_RA)(sp) /* stackframe.record.ra = 0 */
+#ifdef CONFIG_RISCV_M_MODE
+ li t0, SR_MPP
+ and t0, s1, t0
+#else
+ andi t0, s1, SR_SPP
+#endif
+ bnez t0, 1f
+ li t0, FRAME_META_TYPE_FINAL
+ j 2f
+1:
+ li t0, FRAME_META_TYPE_PT_REGS
+2:
+ REG_S t0, S_STACKFRAME_TYPE(sp)
+ addi s0, sp, S_STACKFRAME + STACKFRAME_RECORD_SIZE
+
/*
* Set the scratch register to 0, so that if a recursive exception
* occurs, the exception vector knows it came from the kernel
@@ -354,6 +376,19 @@ SYM_CODE_START_LOCAL(handle_kernel_stack_overflow)
REG_S s3, PT_BADADDR(sp)
REG_S s4, PT_CAUSE(sp)
REG_S s5, PT_TP(sp)
+
+ /*
+ * Create a metadata frame record for the overflow pt_regs. The
+ * overflow path is entered from kernel context, so this is a nested
+ * pt_regs boundary and the unwinder can resume from the pre-overflow
+ * frame pointer saved in PT_S0.
+ */
+ REG_S zero, (S_STACKFRAME + FRAME_RECORD_FP)(sp)
+ REG_S zero, (S_STACKFRAME + FRAME_RECORD_RA)(sp)
+ li t0, FRAME_META_TYPE_PT_REGS
+ REG_S t0, S_STACKFRAME_TYPE(sp)
+ addi s0, sp, S_STACKFRAME + STACKFRAME_RECORD_SIZE
+
move a0, sp
tail handle_bad_stack
SYM_CODE_END(handle_kernel_stack_overflow)
@@ -362,8 +397,8 @@ ASM_NOKPROBE(handle_kernel_stack_overflow)
SYM_CODE_START(ret_from_fork_kernel_asm)
call schedule_tail
- move a0, s1 /* fn_arg */
- move a1, s0 /* fn */
+ move a0, s3 /* fn_arg */
+ move a1, s2 /* fn */
move a2, sp /* pt_regs */
call ret_from_fork_kernel
j ret_from_exception
diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index f6a8ca49e627..341b2d3facbc 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -14,6 +14,7 @@
#include <asm/hwcap.h>
#include <asm/image.h>
#include <asm/scs.h>
+#include <asm/stacktrace/frame.h>
#include <asm/usercfi.h>
#include "efi-header.S"
@@ -177,6 +178,14 @@ secondary_start_sbi:
REG_S a0, (a1)
1:
#endif
+
+ /*
+ * Set up the frame pointer for the secondary idle task so reliable
+ * stack unwinding terminates at the metadata frame in task_pt_regs().
+ * Without this, the first frame records can inherit an undefined caller
+ * fp and unwind past smp_callin() into .Lsecondary_park.
+ */
+ addi s0, sp, S_STACKFRAME + STACKFRAME_RECORD_SIZE
scs_load_current
call smp_callin
#endif /* CONFIG_SMP */
@@ -305,6 +314,20 @@ SYM_CODE_START(_start_kernel)
la tp, init_task
la sp, init_thread_union + THREAD_SIZE
addi sp, sp, -PT_SIZE_ON_STACK
+
+ /*
+ * Set up a metadata frame record for the init task so that
+ * the unwinder can identify the outermost frame by its
+ * {fp, ra} = {0, 0} sentinel at the bottom of pt_regs.
+ * fp/s0 points above the metadata record (RISC-V
+ * convention).
+ */
+ REG_S zero, (S_STACKFRAME + FRAME_RECORD_FP)(sp)
+ REG_S zero, (S_STACKFRAME + FRAME_RECORD_RA)(sp)
+ li t0, FRAME_META_TYPE_FINAL
+ REG_S t0, S_STACKFRAME_TYPE(sp)
+ addi s0, sp, S_STACKFRAME + STACKFRAME_RECORD_SIZE
+
#if defined(CONFIG_RISCV_SBI) && defined(CONFIG_RISCV_USER_CFI)
li a7, SBI_EXT_FWFT
li a6, SBI_EXT_FWFT_SET
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index b2df7f72241a..0dc90bf7a652 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -258,8 +258,23 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
/* Supervisor/Machine, irqs on: */
childregs->status = SR_PP | SR_PIE;
- p->thread.s[0] = (unsigned long)args->fn;
- p->thread.s[1] = (unsigned long)args->fn_arg;
+ /*
+ * Set up a metadata frame record at the bottom of the
+ * stack for the unwinder. Use FRAME_META_TYPE_FINAL
+ * since this is the outermost kernel entry for the new
+ * task. The frame_record::{fp,ra} are already zero from
+ * memset().
+ *
+ * fp/s0 points above the metadata record (RISC-V
+ * convention). fn and fn_arg are passed via s2/s3,
+ * keeping s0 available for the frame pointer chain.
+ */
+ childregs->stackframe.type = FRAME_META_TYPE_FINAL;
+
+ p->thread.s[0] = (unsigned long)(&childregs->stackframe)
+ + sizeof(struct frame_record);
+ p->thread.s[2] = (unsigned long)args->fn;
+ p->thread.s[3] = (unsigned long)args->fn_arg;
p->thread.ra = (unsigned long)ret_from_fork_kernel_asm;
} else {
/* allocate new shadow stack if needed. In case of CLONE_VM we have to */
@@ -278,6 +293,20 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
if (clone_flags & CLONE_SETTLS)
childregs->tp = tls;
childregs->a0 = 0; /* Return value of fork() */
+
+ /*
+ * Set up the unwind boundary: ensure the metadata
+ * frame record has its {fp,ra} sentinel zeroed and
+ * point fp/s0 above the metadata record. Mark it as
+ * FINAL since this is the outermost kernel entry for
+ * the new task.
+ */
+ childregs->stackframe.record.fp = 0;
+ childregs->stackframe.record.ra = 0;
+ childregs->stackframe.type = FRAME_META_TYPE_FINAL;
+ p->thread.s[0] = (unsigned long)(&childregs->stackframe)
+ + sizeof(struct frame_record);
+
p->thread.ra = (unsigned long)ret_from_fork_user_asm;
}
p->thread.riscv_v_flags = 0;
--
2.43.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* [PATCH v5 2/7] riscv: stacktrace: disable KASAN and KCOV instrumentation for stacktrace.o
2026-08-04 10:36 [PATCH v5 0/7] riscv: Add reliable stack unwinding for livepatch Wang Han
2026-08-04 10:36 ` [PATCH v5 1/7] riscv: stacktrace: Add frame record metadata Wang Han
@ 2026-08-04 10:36 ` Wang Han
2026-08-04 10:36 ` [PATCH v5 3/7] riscv: ftrace: always preserve s0 in dynamic ftrace register frame Wang Han
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: Wang Han @ 2026-08-04 10:36 UTC (permalink / raw)
To: Paul Walmsley, Palmer Dabbelt, Albert Ou
Cc: Alexandre Ghiti, linux-riscv, Oleg Nesterov, Steven Rostedt,
Masami Hiramatsu, Mark Rutland, Peter Zijlstra, Ingo Molnar,
Arnaldo Carvalho de Melo, Namhyung Kim, Alexander Shishkin,
Jiri Olsa, Ian Rogers, Adrian Hunter, James Clark, Josh Poimboeuf,
Jiri Kosina, Miroslav Benes, Petr Mladek, Joe Lawrence,
Shuah Khan, oliver.yang, xueshuai, zhuo.song, jkchen,
Marcos Paulo de Souza, linux-kernel, linux-trace-kernel,
linux-perf-users, live-patching, linux-kselftest
KASAN records stack traces for every alloc/free, which means it walks
the unwinder very frequently. Instrumenting the stack trace collection
code itself adds substantial overhead and makes the traces themselves
noisier.
KCOV instruments every basic-block edge. The unwinder is a hot path,
especially with KASAN enabled, so KCOV instrumentation has the same kind
of cost and noise problem here.
Mark stacktrace.o as not KASAN- or KCOV-instrumented, matching the x86
treatment of its stack unwinding code. RISC-V keeps the relevant unwinder
code in stacktrace.o, so a single translation-unit annotation covers the
equivalent scope. This is a prerequisite preference for the upcoming
reliable unwinder, but the change is valid on its own.
Signed-off-by: Wang Han <wanghan@linux.alibaba.com>
---
arch/riscv/kernel/Makefile | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index cabb99cadfb6..c565a72a36f3 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -44,6 +44,12 @@ CFLAGS_REMOVE_return_address.o = $(CC_FLAGS_FTRACE)
CFLAGS_REMOVE_sbi_ecall.o = $(CC_FLAGS_FTRACE)
endif
+# When KASAN is enabled, a stack trace is recorded for every alloc/free, which
+# can significantly impact performance. Avoid instrumenting the stack trace
+# collection code to minimize this impact.
+KASAN_SANITIZE_stacktrace.o := n
+KCOV_INSTRUMENT_stacktrace.o := n
+
always-$(KBUILD_BUILTIN) += vmlinux.lds
obj-y += head.o
--
2.43.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* [PATCH v5 3/7] riscv: ftrace: always preserve s0 in dynamic ftrace register frame
2026-08-04 10:36 [PATCH v5 0/7] riscv: Add reliable stack unwinding for livepatch Wang Han
2026-08-04 10:36 ` [PATCH v5 1/7] riscv: stacktrace: Add frame record metadata Wang Han
2026-08-04 10:36 ` [PATCH v5 2/7] riscv: stacktrace: disable KASAN and KCOV instrumentation for stacktrace.o Wang Han
@ 2026-08-04 10:36 ` Wang Han
2026-08-04 10:36 ` [PATCH v5 4/7] riscv: stacktrace: introduce stack-bound tracking helpers Wang Han
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: Wang Han @ 2026-08-04 10:36 UTC (permalink / raw)
To: Paul Walmsley, Palmer Dabbelt, Albert Ou
Cc: Alexandre Ghiti, linux-riscv, Oleg Nesterov, Steven Rostedt,
Masami Hiramatsu, Mark Rutland, Peter Zijlstra, Ingo Molnar,
Arnaldo Carvalho de Melo, Namhyung Kim, Alexander Shishkin,
Jiri Olsa, Ian Rogers, Adrian Hunter, James Clark, Josh Poimboeuf,
Jiri Kosina, Miroslav Benes, Petr Mladek, Joe Lawrence,
Shuah Khan, oliver.yang, xueshuai, zhuo.song, jkchen,
Marcos Paulo de Souza, linux-kernel, linux-trace-kernel,
linux-perf-users, live-patching, linux-kselftest
struct __arch_ftrace_regs declares s0 unconditionally, and both
ftrace_regs_get_frame_pointer() and ftrace_partial_regs() read it
unconditionally. But the SAVE_ABI_REGS / RESTORE_ABI_REGS macros in
mcount-dyn.S only stored s0 under HAVE_FUNCTION_GRAPH_FP_TEST
(CONFIG_FUNCTION_GRAPH_TRACER && CONFIG_FRAME_POINTER). With
CONFIG_FRAME_POINTER=n the slot held whatever was on the stack before,
so any callback going through ftrace_partial_regs() saw a garbage
regs->s0. RISC-V kernels default to FRAME_POINTER=y, which is why this
has not bitten in practice.
Save and restore s0 unconditionally in the dynamic ftrace ABI register
frame. This fixes the latent garbage-s0 case, brings the dynamic ftrace
path in line with the static _mcount path (mcount.S SAVE_ABI_STATE
already saves s0 unconditionally), and matches the frame layout already
documented in the comment above SAVE_ABI_REGS. It is also a prerequisite
for the upcoming reliable unwinder, which reads
ftrace_regs_get_frame_pointer(fregs) directly.
The cost is one extra REG_S/REG_L pair per traced call, negligible
compared to the overall ftrace cost; the existing FREGS_SIZE_ON_STACK
already reserved the slot, so no extra stack space is used.
Reviewed-by: Shuai Xue <xueshuai@linux.alibaba.com>
Signed-off-by: Wang Han <wanghan@linux.alibaba.com>
---
arch/riscv/kernel/mcount-dyn.S | 4 ----
1 file changed, 4 deletions(-)
diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
index 082fe0b0e3c0..26c55fba8fec 100644
--- a/arch/riscv/kernel/mcount-dyn.S
+++ b/arch/riscv/kernel/mcount-dyn.S
@@ -85,9 +85,7 @@
addi sp, sp, -FREGS_SIZE_ON_STACK
REG_S t0, FREGS_EPC(sp)
REG_S x1, FREGS_RA(sp)
-#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
REG_S x8, FREGS_S0(sp)
-#endif
REG_S x6, FREGS_T1(sp)
#ifdef CONFIG_CC_IS_CLANG
REG_S x7, FREGS_T2(sp)
@@ -113,9 +111,7 @@
.macro RESTORE_ABI_REGS
REG_L t0, FREGS_EPC(sp)
REG_L x1, FREGS_RA(sp)
-#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
REG_L x8, FREGS_S0(sp)
-#endif
REG_L x6, FREGS_T1(sp)
#ifdef CONFIG_CC_IS_CLANG
REG_L x7, FREGS_T2(sp)
--
2.43.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* [PATCH v5 4/7] riscv: stacktrace: introduce stack-bound tracking helpers
2026-08-04 10:36 [PATCH v5 0/7] riscv: Add reliable stack unwinding for livepatch Wang Han
` (2 preceding siblings ...)
2026-08-04 10:36 ` [PATCH v5 3/7] riscv: ftrace: always preserve s0 in dynamic ftrace register frame Wang Han
@ 2026-08-04 10:36 ` Wang Han
2026-08-04 10:36 ` [PATCH v5 5/7] riscv: stacktrace: switch to frame-pointer based unwinder Wang Han
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: Wang Han @ 2026-08-04 10:36 UTC (permalink / raw)
To: Paul Walmsley, Palmer Dabbelt, Albert Ou
Cc: Alexandre Ghiti, linux-riscv, Oleg Nesterov, Steven Rostedt,
Masami Hiramatsu, Mark Rutland, Peter Zijlstra, Ingo Molnar,
Arnaldo Carvalho de Melo, Namhyung Kim, Alexander Shishkin,
Jiri Olsa, Ian Rogers, Adrian Hunter, James Clark, Josh Poimboeuf,
Jiri Kosina, Miroslav Benes, Petr Mladek, Joe Lawrence,
Shuah Khan, oliver.yang, xueshuai, zhuo.song, jkchen,
Marcos Paulo de Souza, linux-kernel, linux-trace-kernel,
linux-perf-users, live-patching, linux-kselftest
A reliable unwinder needs to validate that every frame record it reads
is fully contained in a known kernel stack, and it needs to refuse to
walk back into a stack it has already left. Add the building blocks
for that:
* struct stack_info / struct unwind_state in a new
asm/stacktrace/common.h, modelled on the arm64 reference
implementation.
* stackinfo_get_irq() / stackinfo_get_task() / stackinfo_get_overflow()
plus the corresponding on_*_stack() predicates in asm/stacktrace.h,
so callers can ask "is this object on stack X?" by stack kind
rather than open-coded address arithmetic.
* unwind_init_common(), unwind_find_stack() and
unwind_consume_stack() helpers that enforce the
forward-progress-only invariant required for reliability.
No existing user is wired up to these helpers in this commit; the
unwinder switch comes in a follow-up. The header changes leave
on_thread_stack() with the same semantics as before, just expressed in
terms of the new helpers.
Reviewed-by: Shuai Xue <xueshuai@linux.alibaba.com>
Signed-off-by: Wang Han <wanghan@linux.alibaba.com>
---
arch/riscv/include/asm/stacktrace.h | 67 ++++++++-
arch/riscv/include/asm/stacktrace/common.h | 159 +++++++++++++++++++++
2 files changed, 224 insertions(+), 2 deletions(-)
create mode 100644 arch/riscv/include/asm/stacktrace/common.h
diff --git a/arch/riscv/include/asm/stacktrace.h b/arch/riscv/include/asm/stacktrace.h
index b1495a7e06ce..df4d022f6430 100644
--- a/arch/riscv/include/asm/stacktrace.h
+++ b/arch/riscv/include/asm/stacktrace.h
@@ -3,8 +3,13 @@
#ifndef _ASM_RISCV_STACKTRACE_H
#define _ASM_RISCV_STACKTRACE_H
+#include <linux/percpu.h>
#include <linux/sched.h>
+#include <linux/sched/task_stack.h>
+
+#include <asm/irq_stack.h>
#include <asm/ptrace.h>
+#include <asm/stacktrace/common.h>
struct stackframe {
unsigned long fp;
@@ -16,14 +21,72 @@ extern void notrace walk_stackframe(struct task_struct *task, struct pt_regs *re
extern void dump_backtrace(struct pt_regs *regs, struct task_struct *task,
const char *loglvl);
-static inline bool on_thread_stack(void)
+/*
+ * IRQ stack accessors
+ */
+#ifdef CONFIG_IRQ_STACKS
+static inline struct stack_info stackinfo_get_irq(void)
+{
+ unsigned long low = (unsigned long)raw_cpu_read(irq_stack_ptr);
+ unsigned long high = low + IRQ_STACK_SIZE;
+
+ return (struct stack_info) {
+ .low = low,
+ .high = high,
+ };
+}
+
+static inline bool on_irq_stack(unsigned long sp, unsigned long size)
+{
+ struct stack_info info = stackinfo_get_irq();
+
+ return stackinfo_on_stack(&info, sp, size);
+}
+#endif /* CONFIG_IRQ_STACKS */
+
+/*
+ * Task stack accessors
+ */
+static inline struct stack_info stackinfo_get_task(const struct task_struct *tsk)
{
- return !(((unsigned long)(current->stack) ^ current_stack_pointer) & ~(THREAD_SIZE - 1));
+ unsigned long low = (unsigned long)task_stack_page(tsk);
+ unsigned long high = low + THREAD_SIZE;
+
+ return (struct stack_info) {
+ .low = low,
+ .high = high,
+ };
+}
+
+static inline bool on_task_stack(const struct task_struct *tsk,
+ unsigned long sp, unsigned long size)
+{
+ struct stack_info info = stackinfo_get_task(tsk);
+
+ return stackinfo_on_stack(&info, sp, size);
}
+/*
+ * Cast is necessary since current->stack is an opaque ptr.
+ */
+#define on_thread_stack() (on_task_stack(current, current_stack_pointer, 1))
+/*
+ * Overflow stack accessors
+ */
#ifdef CONFIG_VMAP_STACK
DECLARE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], overflow_stack);
+
+static inline struct stack_info stackinfo_get_overflow(void)
+{
+ unsigned long low = (unsigned long)raw_cpu_ptr(overflow_stack);
+ unsigned long high = low + OVERFLOW_STACK_SIZE;
+
+ return (struct stack_info) {
+ .low = low,
+ .high = high,
+ };
+}
#endif /* CONFIG_VMAP_STACK */
#endif /* _ASM_RISCV_STACKTRACE_H */
diff --git a/arch/riscv/include/asm/stacktrace/common.h b/arch/riscv/include/asm/stacktrace/common.h
new file mode 100644
index 000000000000..360a26e34349
--- /dev/null
+++ b/arch/riscv/include/asm/stacktrace/common.h
@@ -0,0 +1,159 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * RISC-V common stack unwinder types and helpers.
+ *
+ * See: arch/arm64/include/asm/stacktrace/common.h for the reference
+ * implementation.
+ *
+ * Copyright (C) 2026
+ */
+#ifndef __ASM_RISCV_STACKTRACE_COMMON_H
+#define __ASM_RISCV_STACKTRACE_COMMON_H
+
+#include <linux/compiler.h>
+#include <linux/errno.h>
+#include <linux/types.h>
+
+#include <asm/stacktrace/frame.h>
+
+/**
+ * struct stack_info - describes the bounds of a stack.
+ *
+ * @low: The lowest valid address on the stack.
+ * @high: The highest valid address on the stack.
+ */
+struct stack_info {
+ unsigned long low;
+ unsigned long high;
+};
+
+/**
+ * struct unwind_state - state used for robust unwinding.
+ *
+ * @fp: The fp value in the frame record (or the real fp).
+ * @pc: The ra value in the frame record (or the real ra).
+ *
+ * @stack: The stack currently being unwound.
+ * @stacks: An array of stacks which can be unwound.
+ * @nr_stacks: The number of stacks in @stacks.
+ */
+struct unwind_state {
+ unsigned long fp;
+ unsigned long pc;
+
+ struct stack_info stack;
+ struct stack_info *stacks;
+ int nr_stacks;
+};
+
+/**
+ * stackinfo_get_unknown() - Get an unknown stack_info.
+ *
+ * Return: a stack_info with low and high set to 0.
+ */
+static inline struct stack_info stackinfo_get_unknown(void)
+{
+ return (struct stack_info) {
+ .low = 0,
+ .high = 0,
+ };
+}
+
+/**
+ * stackinfo_on_stack() - Check whether an object is fully within a stack.
+ *
+ * @info: The stack to check against.
+ * @sp: The base address of the object.
+ * @size: The size of the object.
+ *
+ * Return: true if the object is fully contained within the stack.
+ */
+static inline bool stackinfo_on_stack(const struct stack_info *info,
+ unsigned long sp, unsigned long size)
+{
+ if (!info->low)
+ return false;
+
+ if (sp < info->low || sp + size < sp || sp + size > info->high)
+ return false;
+
+ return true;
+}
+
+/**
+ * unwind_init_common() - Initialize the common parts of the unwind state.
+ *
+ * @state: the unwind state to initialize.
+ */
+static inline void unwind_init_common(struct unwind_state *state)
+{
+ state->stack = stackinfo_get_unknown();
+}
+
+/**
+ * unwind_find_stack() - Find the accessible stack which entirely contains an
+ * object.
+ *
+ * @state: the current unwind state.
+ * @sp: the base address of the object.
+ * @size: the size of the object.
+ *
+ * Return: a pointer to the relevant stack_info if found; NULL otherwise.
+ */
+static inline struct stack_info *unwind_find_stack(struct unwind_state *state,
+ unsigned long sp,
+ unsigned long size)
+{
+ struct stack_info *info = &state->stack;
+
+ if (stackinfo_on_stack(info, sp, size))
+ return info;
+
+ for (int i = 0; i < state->nr_stacks; i++) {
+ info = &state->stacks[i];
+ if (stackinfo_on_stack(info, sp, size))
+ return info;
+ }
+
+ return NULL;
+}
+
+/**
+ * unwind_consume_stack() - Update stack boundaries so that future unwind steps
+ * cannot consume this object again.
+ *
+ * @state: the current unwind state.
+ * @info: the stack_info of the stack containing the object.
+ * @sp: the base address of the object.
+ * @size: the size of the object.
+ *
+ * Stack transitions are strictly one-way, and once we've
+ * transitioned from one stack to another, it's never valid to
+ * unwind back to the old stack.
+ *
+ * Note that stacks can nest in several valid orders, e.g.
+ *
+ * TASK -> IRQ -> OVERFLOW
+ *
+ * ... so we do not check the specific order of stack
+ * transitions.
+ */
+static inline void unwind_consume_stack(struct unwind_state *state,
+ struct stack_info *info,
+ unsigned long sp,
+ unsigned long size)
+{
+ struct stack_info tmp;
+
+ tmp = *info;
+ *info = stackinfo_get_unknown();
+ state->stack = tmp;
+
+ /*
+ * Future unwind steps can only consume stack above this frame record.
+ * Update the current stack to start immediately above it.
+ */
+ state->stack.low = sp + size;
+}
+
+#endif /* __ASM_RISCV_STACKTRACE_COMMON_H */
--
2.43.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* [PATCH v5 5/7] riscv: stacktrace: switch to frame-pointer based unwinder
2026-08-04 10:36 [PATCH v5 0/7] riscv: Add reliable stack unwinding for livepatch Wang Han
` (3 preceding siblings ...)
2026-08-04 10:36 ` [PATCH v5 4/7] riscv: stacktrace: introduce stack-bound tracking helpers Wang Han
@ 2026-08-04 10:36 ` Wang Han
2026-08-04 10:36 ` [PATCH v5 6/7] riscv: Kconfig: enable HAVE_RELIABLE_STACKTRACE and HAVE_LIVEPATCH Wang Han
2026-08-04 10:36 ` [PATCH v5 7/7] selftests/livepatch: Add RISC-V syscall wrapper prefix Wang Han
6 siblings, 0 replies; 8+ messages in thread
From: Wang Han @ 2026-08-04 10:36 UTC (permalink / raw)
To: Paul Walmsley, Palmer Dabbelt, Albert Ou
Cc: Alexandre Ghiti, linux-riscv, Oleg Nesterov, Steven Rostedt,
Masami Hiramatsu, Mark Rutland, Peter Zijlstra, Ingo Molnar,
Arnaldo Carvalho de Melo, Namhyung Kim, Alexander Shishkin,
Jiri Olsa, Ian Rogers, Adrian Hunter, James Clark, Josh Poimboeuf,
Jiri Kosina, Miroslav Benes, Petr Mladek, Joe Lawrence,
Shuah Khan, oliver.yang, xueshuai, zhuo.song, jkchen,
Marcos Paulo de Souza, linux-kernel, linux-trace-kernel,
linux-perf-users, live-patching, linux-kselftest
Replace the open-coded frame-pointer walker in arch_stack_walk() with a
robust kunwind state machine, modelled on arch/arm64/kernel/stacktrace.c
and retargeted to the RISC-V {fp, ra} frame record convention. The new
walker tracks stack bounds, consumes frame records monotonically,
understands the metadata pt_regs records added in the previous frame
record metadata patch, and recovers return addresses replaced by
function graph tracing and kretprobes.
This commit introduces arch_stack_walk_reliable() but does not yet
select HAVE_RELIABLE_STACKTRACE; that is done in a follow-up Kconfig
patch so this commit can be reviewed and bisected as a pure unwinder
replacement. Until that Kconfig change lands, livepatch is not yet
enabled and arch_stack_walk_reliable() has no in-tree caller.
Three related callers are updated to keep the same frame-record
assumptions everywhere:
* Function graph tracing: the old RISC-V unwinder matched function
graph return-stack entries by the saved return-address slot. That
was consistent with the static mcount path, but not with the dynamic
ftrace path where the parent slot is ftrace_regs::ra. Use the
architectural frame pointer as the function graph return-address
cookie, matching the kunwind walker.
* Perf callchains: route kernel callchain collection through
arch_stack_walk() so perf sees the same frame-pointer unwind
behaviour as dump_stack() and the upcoming livepatch path.
* dump_backtrace() / __get_wchan() / show_stack(): these now go
through arch_stack_walk(); the explicit "Call Trace:" header is
moved into dump_backtrace() to preserve the original output.
The non-frame-pointer fallback walker is kept untouched for
!CONFIG_FRAME_POINTER builds.
Signed-off-by: Wang Han <wanghan@linux.alibaba.com>
---
arch/riscv/kernel/ftrace.c | 6 +-
arch/riscv/kernel/perf_callchain.c | 2 +-
arch/riscv/kernel/stacktrace.c | 561 ++++++++++++++++++++++++-----
3 files changed, 473 insertions(+), 96 deletions(-)
diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index b430edfb83f4..5d55199a9230 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -242,7 +242,8 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
*/
old = *parent;
- if (!function_graph_enter(old, self_addr, frame_pointer, parent))
+ if (!function_graph_enter(old, self_addr, frame_pointer,
+ (void *)frame_pointer))
*parent = return_hooker;
}
@@ -264,7 +265,8 @@ void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
*/
old = *parent;
- if (!function_graph_enter_regs(old, ip, frame_pointer, parent, fregs))
+ if (!function_graph_enter_regs(old, ip, frame_pointer,
+ (void *)frame_pointer, fregs))
*parent = return_hooker;
}
#endif /* CONFIG_DYNAMIC_FTRACE */
diff --git a/arch/riscv/kernel/perf_callchain.c b/arch/riscv/kernel/perf_callchain.c
index b465bc9eb870..436af96ea59c 100644
--- a/arch/riscv/kernel/perf_callchain.c
+++ b/arch/riscv/kernel/perf_callchain.c
@@ -44,5 +44,5 @@ void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
return;
}
- walk_stackframe(NULL, regs, fill_callchain, entry);
+ arch_stack_walk(fill_callchain, entry, NULL, regs);
}
diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
index c7555447149b..0ce0cf0da606 100644
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -11,98 +11,16 @@
#include <linux/sched/task_stack.h>
#include <linux/stacktrace.h>
#include <linux/ftrace.h>
+#include <linux/kprobes.h>
+#include <linux/llist.h>
#include <asm/stacktrace.h>
-#ifdef CONFIG_FRAME_POINTER
-
/*
- * This disables KASAN checking when reading a value from another task's stack,
- * since the other task could be running on another CPU and could have poisoned
- * the stack in the meantime.
+ * Non-frame-pointer fallback unwinder.
+ * Only compiled when CONFIG_FRAME_POINTER is not enabled.
*/
-#define READ_ONCE_TASK_STACK(task, x) \
-({ \
- unsigned long val; \
- unsigned long addr = x; \
- if ((task) == current) \
- val = READ_ONCE(addr); \
- else \
- val = READ_ONCE_NOCHECK(addr); \
- val; \
-})
-
-extern asmlinkage void handle_exception(void);
-extern unsigned long ret_from_exception_end;
-
-static inline int fp_is_valid(unsigned long fp, unsigned long sp)
-{
- unsigned long low, high;
-
- low = sp + sizeof(struct stackframe);
- high = ALIGN(sp, THREAD_SIZE);
-
- return !(fp < low || fp > high || fp & 0x07);
-}
-
-void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
- bool (*fn)(void *, unsigned long), void *arg)
-{
- unsigned long fp, sp, pc;
- int graph_idx = 0;
- int level = 0;
-
- if (regs) {
- fp = frame_pointer(regs);
- sp = user_stack_pointer(regs);
- pc = instruction_pointer(regs);
- } else if (task == NULL || task == current) {
- fp = (unsigned long)__builtin_frame_address(0);
- sp = current_stack_pointer;
- pc = (unsigned long)walk_stackframe;
- level = -1;
- } else {
- /* task blocked in __switch_to */
- fp = task->thread.s[0];
- sp = task->thread.sp;
- pc = task->thread.ra;
- }
-
- for (;;) {
- struct stackframe *frame;
-
- if (unlikely(!__kernel_text_address(pc) || (level++ >= 0 && !fn(arg, pc))))
- break;
-
- if (unlikely(!fp_is_valid(fp, sp)))
- break;
-
- /* Unwind stack frame */
- frame = (struct stackframe *)fp - 1;
- sp = fp;
- if (regs && (regs->epc == pc) && fp_is_valid(frame->ra, sp)) {
- /* We hit function where ra is not saved on the stack */
- fp = frame->ra;
- pc = regs->ra;
- } else {
- fp = READ_ONCE_TASK_STACK(task, frame->fp);
- pc = READ_ONCE_TASK_STACK(task, frame->ra);
- pc = ftrace_graph_ret_addr(task, &graph_idx, pc,
- &frame->ra);
- if (pc >= (unsigned long)handle_exception &&
- pc < (unsigned long)&ret_from_exception_end) {
- if (unlikely(!fn(arg, pc)))
- break;
-
- pc = ((struct pt_regs *)sp)->epc;
- fp = ((struct pt_regs *)sp)->s0;
- }
- }
-
- }
-}
-
-#else /* !CONFIG_FRAME_POINTER */
+#ifndef CONFIG_FRAME_POINTER
void notrace walk_stackframe(struct task_struct *task,
struct pt_regs *regs, bool (*fn)(void *, unsigned long), void *arg)
@@ -133,7 +51,12 @@ void notrace walk_stackframe(struct task_struct *task,
}
}
-#endif /* CONFIG_FRAME_POINTER */
+#endif /* !CONFIG_FRAME_POINTER */
+
+/*
+ * Common trace helpers.
+ * These are used by both the FP (kunwind) and non-FP (walk_stackframe) paths.
+ */
static bool print_trace_address(void *arg, unsigned long pc)
{
@@ -146,12 +69,12 @@ static bool print_trace_address(void *arg, unsigned long pc)
noinline void dump_backtrace(struct pt_regs *regs, struct task_struct *task,
const char *loglvl)
{
- walk_stackframe(task, regs, print_trace_address, (void *)loglvl);
+ printk("%sCall Trace:\n", loglvl);
+ arch_stack_walk(print_trace_address, (void *)loglvl, task, regs);
}
void show_stack(struct task_struct *task, unsigned long *sp, const char *loglvl)
{
- pr_cont("%sCall Trace:\n", loglvl);
dump_backtrace(NULL, task, loglvl);
}
@@ -171,17 +94,469 @@ unsigned long __get_wchan(struct task_struct *task)
if (!try_get_task_stack(task))
return 0;
- walk_stackframe(task, NULL, save_wchan, &pc);
+ arch_stack_walk(save_wchan, &pc, task, NULL);
put_task_stack(task);
return pc;
}
-noinline noinstr void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
- struct task_struct *task, struct pt_regs *regs)
+/*
+ * Frame-pointer-based kernel unwind infrastructure.
+ * Only compiled when CONFIG_FRAME_POINTER is enabled.
+ *
+ * See: arch/arm64/kernel/stacktrace.c for the reference implementation.
+ */
+#ifdef CONFIG_FRAME_POINTER
+
+/*
+ * Per-cpu stacks are only accessible when unwinding the current task in a
+ * non-preemptible context.
+ */
+#define STACKINFO_CPU(task, name) \
+ ({ \
+ (((task) == current) && !preemptible()) \
+ ? stackinfo_get_##name() \
+ : stackinfo_get_unknown(); \
+ })
+
+enum kunwind_source {
+ KUNWIND_SOURCE_UNKNOWN,
+ KUNWIND_SOURCE_FRAME,
+ KUNWIND_SOURCE_CALLER,
+ KUNWIND_SOURCE_TASK,
+ KUNWIND_SOURCE_REGS_PC,
+};
+
+union unwind_flags {
+ unsigned long all;
+ struct {
+ unsigned long fgraph : 1,
+ kretprobe : 1;
+ };
+};
+
+/*
+ * Kernel unwind state
+ *
+ * @common: Common unwind state.
+ * @task: The task being unwound.
+ * @graph_idx: Used by ftrace_graph_ret_addr() for optimized stack unwinding.
+ * @kr_cur: When KRETPROBES is selected, holds the kretprobe instance
+ * associated with the most recently encountered replacement ra
+ * value.
+ */
+struct kunwind_state {
+ struct unwind_state common;
+ struct task_struct *task;
+ int graph_idx;
+#ifdef CONFIG_KRETPROBES
+ struct llist_node *kr_cur;
+#endif
+ enum kunwind_source source;
+ union unwind_flags flags;
+ struct pt_regs *regs;
+};
+
+static __always_inline void
+kunwind_init(struct kunwind_state *state,
+ struct task_struct *task)
+{
+ unwind_init_common(&state->common);
+ state->task = task;
+ state->source = KUNWIND_SOURCE_UNKNOWN;
+ state->flags.all = 0;
+ state->regs = NULL;
+}
+
+/*
+ * Start an unwind from a pt_regs.
+ *
+ * The unwind will begin at the PC within the regs.
+ *
+ * The regs must be on a stack currently owned by the calling task.
+ */
+static __always_inline void
+kunwind_init_from_regs(struct kunwind_state *state,
+ struct pt_regs *regs)
+{
+ kunwind_init(state, current);
+
+ state->regs = regs;
+ state->common.fp = frame_pointer(regs);
+ state->common.pc = instruction_pointer(regs);
+ state->source = KUNWIND_SOURCE_REGS_PC;
+}
+
+/*
+ * Start an unwind from a caller.
+ *
+ * The unwind will begin at the caller of whichever function this is inlined
+ * into.
+ *
+ * The function which invokes this must be noinline.
+ */
+static __always_inline void
+kunwind_init_from_caller(struct kunwind_state *state)
+{
+ unsigned long fp = (unsigned long)__builtin_frame_address(0);
+ struct frame_record *record = (struct frame_record *)fp - 1;
+
+ kunwind_init(state, current);
+
+ state->common.fp = READ_ONCE(record->fp);
+ state->common.pc = READ_ONCE(record->ra);
+ state->source = KUNWIND_SOURCE_CALLER;
+}
+
+/*
+ * Start an unwind from a blocked task.
+ *
+ * The unwind will begin at the blocked task's saved PC (i.e. the caller of
+ * __switch_to).
+ *
+ * The caller should ensure the task is blocked in __switch_to for the
+ * duration of the unwind, or the unwind will be bogus. It is never valid to
+ * call this for the current task.
+ */
+static __always_inline void
+kunwind_init_from_task(struct kunwind_state *state,
+ struct task_struct *task)
+{
+ kunwind_init(state, task);
+
+ state->common.fp = task->thread.s[0];
+ state->common.pc = task->thread.ra;
+ state->source = KUNWIND_SOURCE_TASK;
+}
+
+static __always_inline int
+kunwind_recover_return_address(struct kunwind_state *state)
+{
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ if (state->task->ret_stack &&
+ state->common.pc == (unsigned long)return_to_handler) {
+ unsigned long orig_pc;
+
+ orig_pc = ftrace_graph_ret_addr(state->task, &state->graph_idx,
+ state->common.pc,
+ (void *)state->common.fp);
+ if (state->common.pc == orig_pc) {
+ WARN_ON_ONCE(state->task == current);
+ return -EINVAL;
+ }
+ state->common.pc = orig_pc;
+ state->flags.fgraph = 1;
+ }
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+
+#ifdef CONFIG_KRETPROBES
+ if (is_kretprobe_trampoline(state->common.pc)) {
+ unsigned long orig_pc;
+
+ orig_pc = kretprobe_find_ret_addr(state->task,
+ (void *)state->common.fp,
+ &state->kr_cur);
+ if (!orig_pc)
+ return -EINVAL;
+ state->common.pc = orig_pc;
+ state->flags.kretprobe = 1;
+ }
+#endif /* CONFIG_KRETPROBES */
+
+ return 0;
+}
+
+/*
+ * When we reach an exception boundary marked by a metadata frame record,
+ * extract pt_regs from the stack and continue unwinding from the saved
+ * context (epc and s0/fp).
+ *
+ * On RISC-V, fp points above the metadata record, so the record's
+ * frame_record portion is at fp - sizeof(struct frame_record).
+ */
+static __always_inline int
+kunwind_next_regs_pc(struct kunwind_state *state)
+{
+ struct stack_info *info;
+ unsigned long fp = state->common.fp;
+ struct pt_regs *regs;
+
+ regs = container_of((unsigned long *)(fp - sizeof(struct frame_record)),
+ struct pt_regs, stackframe.record.fp);
+
+ info = unwind_find_stack(&state->common, (unsigned long)regs,
+ sizeof(*regs));
+ if (!info)
+ return -EINVAL;
+
+ unwind_consume_stack(&state->common, info, (unsigned long)regs,
+ sizeof(*regs));
+
+ state->regs = regs;
+ state->common.pc = regs->epc;
+ state->common.fp = frame_pointer(regs);
+ state->source = KUNWIND_SOURCE_REGS_PC;
+ return 0;
+}
+
+/*
+ * Handle a metadata frame record embedded in pt_regs.
+ *
+ * On RISC-V, fp points above the record (fp = metadata + 16), so the
+ * frame_record_meta starts at fp - sizeof(struct frame_record).
+ *
+ * FRAME_META_TYPE_FINAL: This is the outermost exception entry
+ * (user -> kernel). Unwinding terminates successfully.
+ * FRAME_META_TYPE_PT_REGS: This is a nested exception entry
+ * (kernel -> kernel). Continue unwinding from the saved context.
+ */
+static __always_inline int
+kunwind_next_frame_record_meta(struct kunwind_state *state)
+{
+ struct task_struct *tsk = state->task;
+ unsigned long fp = state->common.fp;
+ unsigned long meta_base = fp - sizeof(struct frame_record);
+ struct frame_record_meta *meta;
+ struct stack_info *info;
+
+ info = unwind_find_stack(&state->common, meta_base, sizeof(*meta));
+ if (!info)
+ return -EINVAL;
+
+ meta = (struct frame_record_meta *)meta_base;
+ switch (READ_ONCE(meta->type)) {
+ case FRAME_META_TYPE_FINAL:
+ if (meta == &task_pt_regs(tsk)->stackframe)
+ return -ENOENT;
+ WARN_ON_ONCE(tsk == current);
+ return -EINVAL;
+ case FRAME_META_TYPE_PT_REGS:
+ return kunwind_next_regs_pc(state);
+ default:
+ WARN_ON_ONCE(tsk == current);
+ return -EINVAL;
+ }
+}
+
+/*
+ * Unwind from one frame record to the next.
+ *
+ * On RISC-V, the frame record sits at fp - sizeof(struct frame_record),
+ * immediately below the address pointed to by fp/s0. This applies to both
+ * normal frame records and metadata frame records (embedded in pt_regs).
+ *
+ * A metadata record is identified by both fp and ra being zero in the
+ * frame_record portion, with a type value following at fp + 16.
+ */
+static __always_inline int
+kunwind_next_frame_record(struct kunwind_state *state)
+{
+ unsigned long fp = state->common.fp;
+ struct frame_record *record;
+ struct stack_info *info;
+ unsigned long new_fp, new_pc;
+ unsigned long record_base;
+
+ if (fp & 0x7)
+ return -EINVAL;
+
+ record_base = fp - sizeof(*record);
+
+ info = unwind_find_stack(&state->common, record_base, sizeof(*record));
+ if (!info)
+ return -EINVAL;
+
+ record = (struct frame_record *)record_base;
+ new_fp = READ_ONCE(record->fp);
+ new_pc = READ_ONCE(record->ra);
+
+ if (!new_fp && !new_pc)
+ return kunwind_next_frame_record_meta(state);
+
+ unwind_consume_stack(&state->common, info, record_base,
+ sizeof(*record));
+
+ state->common.fp = new_fp;
+ state->common.pc = new_pc;
+ state->source = KUNWIND_SOURCE_FRAME;
+
+ return 0;
+}
+
+/*
+ * Unwind from one frame record (A) to the next frame record (B).
+ *
+ * We terminate early if the location of B indicates a malformed chain of frame
+ * records (e.g. a cycle), determined based on the location and fp value of A
+ * and the location (but not the fp value) of B.
+ */
+static __always_inline int
+kunwind_next(struct kunwind_state *state)
+{
+ int err;
+
+ state->flags.all = 0;
+
+ switch (state->source) {
+ case KUNWIND_SOURCE_FRAME:
+ case KUNWIND_SOURCE_CALLER:
+ case KUNWIND_SOURCE_TASK:
+ case KUNWIND_SOURCE_REGS_PC:
+ err = kunwind_next_frame_record(state);
+ break;
+ default:
+ err = -EINVAL;
+ }
+
+ if (err)
+ return err;
+
+ return kunwind_recover_return_address(state);
+}
+
+typedef bool (*kunwind_consume_fn)(const struct kunwind_state *state, void *cookie);
+
+static __always_inline int
+do_kunwind(struct kunwind_state *state, kunwind_consume_fn consume_state,
+ void *cookie)
+{
+ int ret;
+
+ ret = kunwind_recover_return_address(state);
+ if (ret)
+ return ret;
+
+ while (1) {
+ if (!consume_state(state, cookie))
+ return -EINVAL;
+ ret = kunwind_next(state);
+ if (ret == -ENOENT)
+ return 0;
+ if (ret < 0)
+ return ret;
+ }
+}
+
+static __always_inline int
+kunwind_stack_walk(kunwind_consume_fn consume_state,
+ void *cookie, struct task_struct *task,
+ struct pt_regs *regs)
+{
+ struct task_struct *tsk = task ?: current;
+ struct stack_info stacks[] = {
+ stackinfo_get_task(tsk),
+#ifdef CONFIG_IRQ_STACKS
+ STACKINFO_CPU(tsk, irq),
+#endif
+#ifdef CONFIG_VMAP_STACK
+ STACKINFO_CPU(tsk, overflow),
+#endif
+ };
+ struct kunwind_state state = {
+ .common = {
+ .stacks = stacks,
+ .nr_stacks = ARRAY_SIZE(stacks),
+ },
+ };
+
+ if (regs) {
+ if (tsk != current)
+ return -EINVAL;
+ kunwind_init_from_regs(&state, regs);
+ } else if (tsk == current) {
+ kunwind_init_from_caller(&state);
+ } else {
+ kunwind_init_from_task(&state, tsk);
+ }
+
+ return do_kunwind(&state, consume_state, cookie);
+}
+
+struct kunwind_consume_entry_data {
+ stack_trace_consume_fn consume_entry;
+ void *cookie;
+};
+
+static __always_inline bool
+arch_kunwind_consume_entry(const struct kunwind_state *state, void *cookie)
+{
+ struct kunwind_consume_entry_data *data = cookie;
+
+ return data->consume_entry(data->cookie, state->common.pc);
+}
+
+static __always_inline bool
+arch_reliable_kunwind_consume_entry(const struct kunwind_state *state, void *cookie)
+{
+ /*
+ * At an exception boundary we can reliably consume the saved PC. We do
+ * not know whether ra was live when the exception was taken, and
+ * so we cannot perform the next unwind step reliably.
+ *
+ * All that matters is whether the *entire* unwind is reliable, so give
+ * up as soon as we hit an exception boundary.
+ */
+ if (state->source == KUNWIND_SOURCE_REGS_PC)
+ return false;
+
+ return arch_kunwind_consume_entry(state, cookie);
+}
+
+#endif /* CONFIG_FRAME_POINTER */
+
+/*
+ * arch_stack_walk - dual implementation.
+ *
+ * When CONFIG_FRAME_POINTER is enabled, uses the kunwind infrastructure for
+ * robust frame-pointer-based unwinding, consistent with arch_stack_walk_reliable.
+ *
+ * When CONFIG_FRAME_POINTER is disabled, falls back to the simple stack scan
+ * in walk_stackframe().
+ */
+#ifdef CONFIG_FRAME_POINTER
+
+noinline noinstr void arch_stack_walk(stack_trace_consume_fn consume_entry,
+ void *cookie, struct task_struct *task,
+ struct pt_regs *regs)
+{
+ struct kunwind_consume_entry_data data = {
+ .consume_entry = consume_entry,
+ .cookie = cookie,
+ };
+
+ kunwind_stack_walk(arch_kunwind_consume_entry, &data, task, regs);
+}
+
+#else
+
+noinline noinstr void arch_stack_walk(stack_trace_consume_fn consume_entry,
+ void *cookie, struct task_struct *task,
+ struct pt_regs *regs)
{
walk_stackframe(task, regs, consume_entry, cookie);
}
+#endif /* CONFIG_FRAME_POINTER */
+
+/*
+ * Reliable stack walk for livepatch (CONFIG_FRAME_POINTER only).
+ */
+#ifdef CONFIG_FRAME_POINTER
+
+noinline noinstr int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry,
+ void *cookie,
+ struct task_struct *task)
+{
+ struct kunwind_consume_entry_data data = {
+ .consume_entry = consume_entry,
+ .cookie = cookie,
+ };
+
+ return kunwind_stack_walk(arch_reliable_kunwind_consume_entry, &data,
+ task, NULL);
+}
+
+#endif /* CONFIG_FRAME_POINTER */
+
/*
* Get the return address for a single stackframe and return a pointer to the
* next frame tail.
--
2.43.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* [PATCH v5 6/7] riscv: Kconfig: enable HAVE_RELIABLE_STACKTRACE and HAVE_LIVEPATCH
2026-08-04 10:36 [PATCH v5 0/7] riscv: Add reliable stack unwinding for livepatch Wang Han
` (4 preceding siblings ...)
2026-08-04 10:36 ` [PATCH v5 5/7] riscv: stacktrace: switch to frame-pointer based unwinder Wang Han
@ 2026-08-04 10:36 ` Wang Han
2026-08-04 10:36 ` [PATCH v5 7/7] selftests/livepatch: Add RISC-V syscall wrapper prefix Wang Han
6 siblings, 0 replies; 8+ messages in thread
From: Wang Han @ 2026-08-04 10:36 UTC (permalink / raw)
To: Paul Walmsley, Palmer Dabbelt, Albert Ou
Cc: Alexandre Ghiti, linux-riscv, Oleg Nesterov, Steven Rostedt,
Masami Hiramatsu, Mark Rutland, Peter Zijlstra, Ingo Molnar,
Arnaldo Carvalho de Melo, Namhyung Kim, Alexander Shishkin,
Jiri Olsa, Ian Rogers, Adrian Hunter, James Clark, Josh Poimboeuf,
Jiri Kosina, Miroslav Benes, Petr Mladek, Joe Lawrence,
Shuah Khan, oliver.yang, xueshuai, zhuo.song, jkchen,
Marcos Paulo de Souza, linux-kernel, linux-trace-kernel,
linux-perf-users, live-patching, linux-kselftest
Now that the metadata frame records, the kunwind state machine and
arch_stack_walk_reliable() are all in place, advertise the capability
to the rest of the kernel:
* select HAVE_RELIABLE_STACKTRACE under FRAME_POINTER && 64BIT, so
only the configurations with the tested metadata records and
FP-based reliable walker enable it.
* select HAVE_LIVEPATCH under the same condition and source
kernel/livepatch/Kconfig so the livepatch menu is reachable from
the RISC-V configuration.
The 64BIT dependency is conservative scoping rather than a hard
technical requirement: the metadata frame record, kunwind state machine
and arch_stack_walk_reliable() also build on RV32, and the IRQ-stack
frame-record adjustment fixes a latent RV32 issue. However, the syscall
livepatch selftest and module relocation path have only been exercised
on RV64 QEMU virt so far. The 64BIT gate can be relaxed in a follow-up
once RV32 has equivalent coverage.
This is split out from the unwinder change so the policy decision and
the implementation can be reviewed and reverted independently.
Reviewed-by: Shuai Xue <xueshuai@linux.alibaba.com>
Signed-off-by: Wang Han <wanghan@linux.alibaba.com>
---
arch/riscv/Kconfig | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index c2c2f5f3ed5e..b36f711ecf45 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -186,6 +186,7 @@ config RISCV
select HAVE_KRETPROBES
# https://github.com/ClangBuiltLinux/linux/issues/1881
select HAVE_LD_DEAD_CODE_DATA_ELIMINATION if !LD_IS_LLD
+ select HAVE_LIVEPATCH if FRAME_POINTER && 64BIT
select HAVE_MOVE_PMD
select HAVE_MOVE_PUD
select HAVE_PAGE_SIZE_4KB
@@ -196,6 +197,7 @@ config RISCV
select HAVE_POSIX_CPU_TIMERS_TASK_WORK
select HAVE_PREEMPT_DYNAMIC_KEY
select HAVE_REGS_AND_STACK_ACCESS_API
+ select HAVE_RELIABLE_STACKTRACE if FRAME_POINTER && 64BIT
select HAVE_RETHOOK
select HAVE_RSEQ
select HAVE_RUST if RUSTC_SUPPORTS_RISCV && CC_IS_CLANG
@@ -1392,3 +1394,5 @@ endmenu # "CPU Power Management"
source "arch/riscv/kvm/Kconfig"
source "drivers/acpi/Kconfig"
+
+source "kernel/livepatch/Kconfig"
--
2.43.0
^ permalink raw reply related [flat|nested] 8+ messages in thread* [PATCH v5 7/7] selftests/livepatch: Add RISC-V syscall wrapper prefix
2026-08-04 10:36 [PATCH v5 0/7] riscv: Add reliable stack unwinding for livepatch Wang Han
` (5 preceding siblings ...)
2026-08-04 10:36 ` [PATCH v5 6/7] riscv: Kconfig: enable HAVE_RELIABLE_STACKTRACE and HAVE_LIVEPATCH Wang Han
@ 2026-08-04 10:36 ` Wang Han
6 siblings, 0 replies; 8+ messages in thread
From: Wang Han @ 2026-08-04 10:36 UTC (permalink / raw)
To: Paul Walmsley, Palmer Dabbelt, Albert Ou
Cc: Alexandre Ghiti, linux-riscv, Oleg Nesterov, Steven Rostedt,
Masami Hiramatsu, Mark Rutland, Peter Zijlstra, Ingo Molnar,
Arnaldo Carvalho de Melo, Namhyung Kim, Alexander Shishkin,
Jiri Olsa, Ian Rogers, Adrian Hunter, James Clark, Josh Poimboeuf,
Jiri Kosina, Miroslav Benes, Petr Mladek, Joe Lawrence,
Shuah Khan, oliver.yang, xueshuai, zhuo.song, jkchen,
Marcos Paulo de Souza, linux-kernel, linux-trace-kernel,
linux-perf-users, live-patching, linux-kselftest
The syscall livepatch selftest resolves and patches a syscall wrapper
symbol. To use that test for RISC-V livepatch validation, add the
RISC-V FN_PREFIX definition for ARCH_HAS_SYSCALL_WRAPPER.
Without this macro, the syscall livepatch selftest cannot resolve the
RISC-V target symbol, and the syscall-related livepatch test fails on
RISC-V.
Reviewed-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Reviewed-by: Shuai Xue <xueshuai@linux.alibaba.com>
Signed-off-by: Wang Han <wanghan@linux.alibaba.com>
---
.../testing/selftests/livepatch/test_modules/test_klp_syscall.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/tools/testing/selftests/livepatch/test_modules/test_klp_syscall.c b/tools/testing/selftests/livepatch/test_modules/test_klp_syscall.c
index 08aacc0e14de..9baa2a5f84c9 100644
--- a/tools/testing/selftests/livepatch/test_modules/test_klp_syscall.c
+++ b/tools/testing/selftests/livepatch/test_modules/test_klp_syscall.c
@@ -24,6 +24,8 @@
#define FN_PREFIX __s390x_
#elif defined(__aarch64__)
#define FN_PREFIX __arm64_
+ #elif defined(__riscv)
+ #define FN_PREFIX __riscv_
#elif defined(__powerpc__)
#define FN_PREFIX
#else
--
2.43.0
^ permalink raw reply related [flat|nested] 8+ messages in thread