[PATCH v4 7/8] sframe: Introduce in-kernel SFRAME_VALIDATION

Dylan Hatch
2026-04-21T22:52:28Z

Generalize the __safe* helpers to support a non-user-access code path.

This requires arch-specific function address validation. This is because
arm64 vmlinux has an .rodata.text section which lies outside the bounds
of the normal .text. It contains code that is never executed by the
kernel mapping, but for which the toolchain nonetheless generates sframe
data, and needs to be considered valid for a PC lookup.

This arch-specific address validation logic is only necessary to support
SFRAME_VALIDATION for the vmlinux .sframe, since these .rodata.text
functions would never be encountered during normal unwinding.

Signed-off-by: Dylan Hatch <dylanbhatch@google.com>
Suggested-by: Jens Remus <jremus@linux.ibm.com>
---
arch/Kconfig | 2 +-
arch/arm64/include/asm/sections.h | 1 +
arch/arm64/include/asm/unwind_sframe.h | 21 +++++++++++++++++++++
arch/arm64/kernel/vmlinux.lds.S | 2 ++
include/linux/sframe.h | 2 ++
kernel/unwind/sframe.c | 25 +++++++++++++++++++++++--
6 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 8d27b3249e7a..cd4849bb675c 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -503,7 +503,7 @@ config HAVE_UNWIND_USER_SFRAME

config SFRAME_VALIDATION
bool "Enable .sframe section debugging"
- depends on HAVE_UNWIND_USER_SFRAME
+ depends on SFRAME_LOOKUP
depends on DYNAMIC_DEBUG
help
When adding an .sframe section for a task, validate the entire
diff --git a/arch/arm64/include/asm/sections.h b/arch/arm64/include/asm/sections.h
index 51b0d594239e..5edb4304f661 100644
--- a/arch/arm64/include/asm/sections.h
+++ b/arch/arm64/include/asm/sections.h
@@ -23,6 +23,7 @@ extern char __irqentry_text_start[], __irqentry_text_end[];
extern char __mmuoff_data_start[], __mmuoff_data_end[];
extern char __entry_tramp_text_start[], __entry_tramp_text_end[];
extern char __relocate_new_kernel_start[], __relocate_new_kernel_end[];
+extern char _srodatatext[], _erodatatext[];

static inline size_t entry_tramp_text_size(void)
{
diff --git a/arch/arm64/include/asm/unwind_sframe.h b/arch/arm64/include/asm/unwind_sframe.h
index 876412881196..1e9d7b74c0c8 100644
--- a/arch/arm64/include/asm/unwind_sframe.h
+++ b/arch/arm64/include/asm/unwind_sframe.h
@@ -2,7 +2,28 @@
#ifndef _ASM_ARM64_UNWIND_SFRAME_H
#define _ASM_ARM64_UNWIND_SFRAME_H

+#include <linux/sframe.h>
+#include <asm/sections.h>
+
#define SFRAME_REG_SP 31
#define SFRAME_REG_FP 29

+static inline bool sframe_func_start_addr_valid(struct sframe_section *sec,
+ unsigned long func_addr)
+{
+ /*
+ * The .rodata.text section is outside the normal kernel .text, but the
+ * toolchain still generates sframe data for it. Allow sframe lookups
+ * for these functions, even though they are never executed from the
+ * kernel mapping.
+ */
+ if (sec->sec_type == SFRAME_KERNEL && sec == &kernel_sfsec &&
+ func_addr >= (unsigned long)_srodatatext &&
+ func_addr < (unsigned long)_erodatatext)
+ return true;
+
+ return (sec->text_start <= func_addr && func_addr < sec->text_end);
+}
+#define sframe_func_start_addr_valid sframe_func_start_addr_valid
+
#endif /* _ASM_ARM64_UNWIND_SFRAME_H */
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 2964aad0362e..8c2dae6e7a86 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -213,12 +213,14 @@ SECTIONS

/* code sections that are never executed via the kernel mapping */
.rodata.text : {
+ _srodatatext = .;
TRAMP_TEXT
HIBERNATE_TEXT
KEXEC_TEXT
IDMAP_TEXT
. = ALIGN(PAGE_SIZE);
}
+ _erodatatext = .;

idmap_pg_dir = .;
. += PAGE_SIZE;
diff --git a/include/linux/sframe.h b/include/linux/sframe.h
index 27f5a66190af..ac3aa9db7d91 100644
--- a/include/linux/sframe.h
+++ b/include/linux/sframe.h
@@ -34,6 +34,8 @@ struct sframe_section {
signed char fp_off;
};

+extern struct sframe_section kernel_sfsec __ro_after_init;
+
#endif /* CONFIG_UNWIND_SFRAME_LOOKUP */

#ifdef CONFIG_HAVE_UNWIND_USER_SFRAME
diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
index 20178e02f428..d76968547bad 100644
--- a/kernel/unwind/sframe.c
+++ b/kernel/unwind/sframe.c
@@ -21,10 +21,18 @@
#include "sframe.h"
#include "sframe_debug.h"

+#ifndef sframe_func_start_addr_valid
+static inline bool sframe_func_start_addr_valid(struct sframe_section *sec,
+ unsigned long func_addr)
+{
+ return (sec->text_start <= func_addr && func_addr < sec->text_end);
+}
+#endif
+
#ifdef CONFIG_HAVE_UNWIND_KERNEL_SFRAME

static bool sframe_init __ro_after_init;
-static struct sframe_section kernel_sfsec __ro_after_init;
+struct sframe_section kernel_sfsec __ro_after_init;

#endif /* CONFIG_HAVE_UNWIND_KERNEL_SFRAME */

@@ -152,7 +160,7 @@ static __always_inline int __read_fde(struct sframe_section *sec,
sizeof(struct sframe_fde_v3), Efault);

func_addr = fde_addr + _fde.func_start_off;
- if (func_addr < sec->text_start || func_addr > sec->text_end)
+ if (!sframe_func_start_addr_valid(sec, func_addr))
return -EINVAL;

fda_addr = sec->fres_start + _fde.fres_off;
@@ -636,6 +644,9 @@ static int safe_read_fde(struct sframe_section *sec,
{
int ret;

+ if (sec->sec_type == SFRAME_KERNEL)
+ return __read_fde(sec, fde_num, fde);
+
if (!user_read_access_begin((void __user *)sec->sframe_start,
sec->sframe_end - sec->sframe_start))
return -EFAULT;
@@ -651,6 +662,9 @@ static int safe_read_fre(struct sframe_section *sec,
{
int ret;

+ if (sec->sec_type == SFRAME_KERNEL)
+ return __read_fre(sec, fde, fre_addr, fre);
+
if (!user_read_access_begin((void __user *)sec->sframe_start,
sec->sframe_end - sec->sframe_start))
return -EFAULT;
@@ -665,6 +679,9 @@ static int safe_read_fre_datawords(struct sframe_section *sec,
{
int ret;

+ if (sec->sec_type == SFRAME_KERNEL)
+ return __read_fre_datawords(sec, fde, fre);
+
if (!user_read_access_begin((void __user *)sec->sframe_start,
sec->sframe_end - sec->sframe_start))
return -EFAULT;
@@ -1013,6 +1030,8 @@ void __init init_sframe_table(void)

if (WARN_ON(sframe_read_header(&kernel_sfsec)))
return;
+ if (WARN_ON(sframe_validate_section(&kernel_sfsec)))
+ return;

sframe_init = true;
}
@@ -1031,6 +1050,8 @@ void sframe_module_init(struct module *mod, void *sframe, size_t sframe_size,

if (WARN_ON(sframe_read_header(&sec)))
return;
+ if (WARN_ON(sframe_validate_section(&sec)))
+ return;

mod->arch.sframe_sec = sec;
mod->arch.sframe_init = true;
--
2.54.0.rc1.555.g9c883467ad-goog