[PATCH 6.12] x86/fgraph: Fix return_to_handler regs.rsp value

[PATCH 6.12] x86/fgraph: Fix return_to_handler regs.rsp value

[Gyokhan Kochmarla]

From: Jiri Olsa <jolsa@kernel.org>

commit 8bc11700e0d23d4fdb7d8d5a73b2e95de427cabc upstream.

The previous change (Fixes commit) messed up the rsp register value,
which is wrong because it's already adjusted with FRAME_SIZE, we need
the original rsp value.

This change does not affect fprobe current kernel unwind, the !perf_hw_regs
path perf_callchain_kernel:

        if (perf_hw_regs(regs)) {
                if (perf_callchain_store(entry, regs->ip))
                        return;
                unwind_start(&state, current, regs, NULL);
        } else {
                unwind_start(&state, current, NULL, (void *)regs->sp);
        }

which uses pt_regs.sp as first_frame boundary (FRAME_SIZE shift makes
no difference, unwind stil stops at the right frame).

This change fixes the other path when we want to unwind directly from
pt_regs sp/fp/ip state, which is coming in following change.

Fixes: 20a0bc10272f ("x86/fgraph,bpf: Fix stack ORC unwind from kprobe_multi return probe")
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/bpf/20260126211837.472802-2-jolsa@kernel.org
Signed-off-by: Gyokhan Kochmarla <gyokhan@amazon.de>
---
 arch/x86/kernel/ftrace_64.S | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index 8a3cff618692..143fc62bf6f8 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -349,6 +349,9 @@ SYM_CODE_START(return_to_handler)
 	UNWIND_HINT_UNDEFINED
 	ANNOTATE_NOENDBR
 
+	/* Store original rsp for pt_regs.sp value. */
+	movq %rsp, %rdi
+
 	/* Restore return_to_handler value that got eaten by previous ret instruction. */
 	subq $8, %rsp
 	UNWIND_HINT_FUNC
@@ -359,7 +362,7 @@ SYM_CODE_START(return_to_handler)
 	movq %rax, RAX(%rsp)
 	movq %rdx, RDX(%rsp)
 	movq %rbp, RBP(%rsp)
-	movq %rsp, RSP(%rsp)
+	movq %rdi, RSP(%rsp)
 	movq %rsp, %rdi
 
 	call ftrace_return_to_handler
-- 
2.47.3




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Re: [PATCH 6.12] x86/fgraph: Fix return_to_handler regs.rsp value

[Sasha Levin]

> commit 8bc11700e0d23d4fdb7d8d5a73b2e95de427cabc upstream.

Queued for 6.12.y, thanks.

--
Thanks,
Sasha