[PATCH v6 05/18] unwind_user: Add compat mode frame pointer support

Steven Rostedt
2025-04-25T14:56:14Z

Add optional support for user space compat mode frame pointer unwinding.
If supported, the arch needs to enable CONFIG_HAVE_UNWIND_USER_COMPAT_FP
and define ARCH_INIT_USER_COMPAT_FP_FRAME.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
arch/Kconfig | 4 +++
include/asm-generic/Kbuild | 2 ++
include/asm-generic/unwind_user.h | 15 +++++++++++
include/asm-generic/unwind_user_types.h | 9 +++++++
include/linux/unwind_user_types.h | 3 +++
kernel/unwind/user.c | 36 ++++++++++++++++++++++---
6 files changed, 65 insertions(+), 4 deletions(-)
create mode 100644 include/asm-generic/unwind_user_types.h

diff --git a/arch/Kconfig b/arch/Kconfig
index 0e3844c0e200..dbb1cc89e040 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -442,6 +442,10 @@ config HAVE_UNWIND_USER_FP
bool
select UNWIND_USER

+config HAVE_UNWIND_USER_COMPAT_FP
+ bool
+ depends on HAVE_UNWIND_USER_FP
+
config HAVE_PERF_REGS
bool
help
diff --git a/include/asm-generic/Kbuild b/include/asm-generic/Kbuild
index 8675b7b4ad23..b797a2434396 100644
--- a/include/asm-generic/Kbuild
+++ b/include/asm-generic/Kbuild
@@ -59,6 +59,8 @@ mandatory-y += tlbflush.h
mandatory-y += topology.h
mandatory-y += trace_clock.h
mandatory-y += uaccess.h
+mandatory-y += unwind_user.h
+mandatory-y += unwind_user_types.h
mandatory-y += vermagic.h
mandatory-y += vga.h
mandatory-y += video.h
diff --git a/include/asm-generic/unwind_user.h b/include/asm-generic/unwind_user.h
index 832425502fb3..385638ce4aec 100644
--- a/include/asm-generic/unwind_user.h
+++ b/include/asm-generic/unwind_user.h
@@ -2,8 +2,23 @@
#ifndef _ASM_GENERIC_UNWIND_USER_H
#define _ASM_GENERIC_UNWIND_USER_H

+#include <asm/unwind_user_types.h>
+
#ifndef ARCH_INIT_USER_FP_FRAME
#define ARCH_INIT_USER_FP_FRAME
#endif

+#ifndef ARCH_INIT_USER_COMPAT_FP_FRAME
+ #define ARCH_INIT_USER_COMPAT_FP_FRAME
+ #define in_compat_mode(regs) false
+#endif
+
+#ifndef arch_unwind_user_init
+static inline void arch_unwind_user_init(struct unwind_user_state *state, struct pt_regs *reg) {}
+#endif
+
+#ifndef arch_unwind_user_next
+static inline void arch_unwind_user_next(struct unwind_user_state *state) {}
+#endif
+
#endif /* _ASM_GENERIC_UNWIND_USER_H */
diff --git a/include/asm-generic/unwind_user_types.h b/include/asm-generic/unwind_user_types.h
new file mode 100644
index 000000000000..ee803de7c998
--- /dev/null
+++ b/include/asm-generic/unwind_user_types.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_GENERIC_UNWIND_USER_TYPES_H
+#define _ASM_GENERIC_UNWIND_USER_TYPES_H
+
+#ifndef arch_unwind_user_state
+struct arch_unwind_user_state {};
+#endif
+
+#endif /* _ASM_GENERIC_UNWIND_USER_TYPES_H */
diff --git a/include/linux/unwind_user_types.h b/include/linux/unwind_user_types.h
index 65bd070eb6b0..3ec4a097a3dd 100644
--- a/include/linux/unwind_user_types.h
+++ b/include/linux/unwind_user_types.h
@@ -3,10 +3,12 @@
#define _LINUX_UNWIND_USER_TYPES_H

#include <linux/types.h>
+#include <asm/unwind_user_types.h>

enum unwind_user_type {
UNWIND_USER_TYPE_NONE,
UNWIND_USER_TYPE_FP,
+ UNWIND_USER_TYPE_COMPAT_FP,
};

struct unwind_stacktrace {
@@ -25,6 +27,7 @@ struct unwind_user_state {
unsigned long ip;
unsigned long sp;
unsigned long fp;
+ struct arch_unwind_user_state arch;
enum unwind_user_type type;
bool done;
};
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index 73fd4e150dfd..92963f129c6a 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -13,12 +13,32 @@ static struct unwind_user_frame fp_frame = {
ARCH_INIT_USER_FP_FRAME
};

+static struct unwind_user_frame compat_fp_frame = {
+ ARCH_INIT_USER_COMPAT_FP_FRAME
+};
+
static inline bool fp_state(struct unwind_user_state *state)
{
return IS_ENABLED(CONFIG_HAVE_UNWIND_USER_FP) &&
state->type == UNWIND_USER_TYPE_FP;
}

+static inline bool compat_state(struct unwind_user_state *state)
+{
+ return IS_ENABLED(CONFIG_HAVE_UNWIND_USER_COMPAT_FP) &&
+ state->type == UNWIND_USER_TYPE_COMPAT_FP;
+}
+
+#define UNWIND_GET_USER_LONG(to, from, state) \
+({ \
+ int __ret; \
+ if (compat_state(state)) \
+ __ret = get_user(to, (u32 __user *)(from)); \
+ else \
+ __ret = get_user(to, (u64 __user *)(from)); \
+ __ret; \
+})
+
int unwind_user_next(struct unwind_user_state *state)
{
struct unwind_user_frame _frame;
@@ -28,7 +48,9 @@ int unwind_user_next(struct unwind_user_state *state)
if (state->done)
return -EINVAL;

- if (fp_state(state))
+ if (compat_state(state))
+ frame = &compat_fp_frame;
+ else if (fp_state(state))
frame = &fp_frame;
else
goto the_end;
@@ -39,10 +61,10 @@ int unwind_user_next(struct unwind_user_state *state)
if (cfa <= state->sp)
goto the_end;

- if (get_user(ra, (unsigned long *)(cfa + frame->ra_off)))
+ if (UNWIND_GET_USER_LONG(ra, cfa + frame->ra_off, state))
goto the_end;

- if (frame->fp_off && get_user(fp, (unsigned long __user *)(cfa + frame->fp_off)))
+ if (frame->fp_off && UNWIND_GET_USER_LONG(fp, cfa + frame->fp_off, state))
goto the_end;

state->ip = ra;
@@ -50,6 +72,8 @@ int unwind_user_next(struct unwind_user_state *state)
if (frame->fp_off)
state->fp = fp;

+ arch_unwind_user_next(state);
+
return 0;

the_end:
@@ -68,7 +92,9 @@ int unwind_user_start(struct unwind_user_state *state)
return -EINVAL;
}

- if (IS_ENABLED(CONFIG_HAVE_UNWIND_USER_FP))
+ if (IS_ENABLED(CONFIG_HAVE_UNWIND_USER_COMPAT_FP) && in_compat_mode(regs))
+ state->type = UNWIND_USER_TYPE_COMPAT_FP;
+ else if (IS_ENABLED(CONFIG_HAVE_UNWIND_USER_FP))
state->type = UNWIND_USER_TYPE_FP;
else
state->type = UNWIND_USER_TYPE_NONE;
@@ -77,6 +103,8 @@ int unwind_user_start(struct unwind_user_state *state)
state->sp = user_stack_pointer(regs);
state->fp = frame_pointer(regs);

+ arch_unwind_user_init(state, regs);
+
return 0;
}

--
2.47.2