[PATCH 6.18 095/314] unwind: Implement compat fp unwind

Sasha Levin
2026-03-10T11:26:10Z

From: Peter Zijlstra <peterz@infradead.org>

[ Upstream commit c79dd946e370af3537edb854f210cba3a94b4516 ]

It is important to be able to unwind compat tasks too.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20250924080119.613695709@infradead.org
Stable-dep-of: d55c571e4333 ("x86/uprobes: Fix XOL allocation failure for 32-bit tasks")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/unwind_user_types.h | 1 +
kernel/unwind/user.c | 40 ++++++++++++++++++++++---------
2 files changed, 30 insertions(+), 11 deletions(-)

diff --git a/include/linux/unwind_user_types.h b/include/linux/unwind_user_types.h
index a449f15be8902..938f7e6233327 100644
--- a/include/linux/unwind_user_types.h
+++ b/include/linux/unwind_user_types.h
@@ -36,6 +36,7 @@ struct unwind_user_state {
unsigned long ip;
unsigned long sp;
unsigned long fp;
+ unsigned int ws;
enum unwind_user_type current_type;
unsigned int available_types;
bool done;
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index 9dcde797b5d93..642871527a132 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -8,19 +8,32 @@
#include <linux/unwind_user.h>
#include <linux/uaccess.h>

-static const struct unwind_user_frame fp_frame = {
- ARCH_INIT_USER_FP_FRAME
-};
-
#define for_each_user_frame(state) \
for (unwind_user_start(state); !(state)->done; unwind_user_next(state))

+static inline int
+get_user_word(unsigned long *word, unsigned long base, int off, unsigned int ws)
+{
+ unsigned long __user *addr = (void __user *)base + off;
+#ifdef CONFIG_COMPAT
+ if (ws == sizeof(int)) {
+ unsigned int data;
+ int ret = get_user(data, (unsigned int __user *)addr);
+ *word = data;
+ return ret;
+ }
+#endif
+ return get_user(*word, addr);
+}
+
static int unwind_user_next_fp(struct unwind_user_state *state)
{
- const struct unwind_user_frame *frame = &fp_frame;
+ const struct unwind_user_frame frame = {
+ ARCH_INIT_USER_FP_FRAME(state->ws)
+ };
unsigned long cfa, fp, ra;

- if (frame->use_fp) {
+ if (frame.use_fp) {
if (state->fp < state->sp)
return -EINVAL;
cfa = state->fp;
@@ -29,26 +42,26 @@ static int unwind_user_next_fp(struct unwind_user_state *state)
}

/* Get the Canonical Frame Address (CFA) */
- cfa += frame->cfa_off;
+ cfa += frame.cfa_off;

/* stack going in wrong direction? */
if (cfa <= state->sp)
return -EINVAL;

/* Make sure that the address is word aligned */
- if (cfa & (sizeof(long) - 1))
+ if (cfa & (state->ws - 1))
return -EINVAL;

/* Find the Return Address (RA) */
- if (get_user(ra, (unsigned long *)(cfa + frame->ra_off)))
+ if (get_user_word(&ra, cfa, frame.ra_off, state->ws))
return -EINVAL;

- if (frame->fp_off && get_user(fp, (unsigned long __user *)(cfa + frame->fp_off)))
+ if (frame.fp_off && get_user_word(&fp, cfa, frame.fp_off, state->ws))
return -EINVAL;

state->ip = ra;
state->sp = cfa;
- if (frame->fp_off)
+ if (frame.fp_off)
state->fp = fp;
return 0;
}
@@ -100,6 +113,11 @@ static int unwind_user_start(struct unwind_user_state *state)
state->ip = instruction_pointer(regs);
state->sp = user_stack_pointer(regs);
state->fp = frame_pointer(regs);
+ state->ws = unwind_user_word_size(regs);
+ if (!state->ws) {
+ state->done = true;
+ return -EINVAL;
+ }

return 0;
}
--
2.51.0