[tip: perf/core] unwind: Implement compat fp unwind

["tip-bot2 for Peter Zijlstra" <tip-bot2@linutronix.de>]

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     c79dd946e370af3537edb854f210cba3a94b4516
Gitweb:        https://git.kernel.org/tip/c79dd946e370af3537edb854f210cba3a94b4516
Author:        Peter Zijlstra <peterz@infradead.org>
AuthorDate:    Tue, 23 Sep 2025 13:27:34 +02:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Wed, 29 Oct 2025 10:29:57 +01:00

unwind: Implement compat fp unwind

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
---
 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 a449f15..938f7e6 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 9dcde79..6428715 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;
 }