x86/fgraph: Fix return_to_handler regs.rsp value

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

diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index a132608265f6c01cc23b20b2361c611043930793..62c1c93aa1c6a624b3db215d076aaea78653940d 100644 (file)
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -364,6 +364,9 @@ 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
@@ -374,7 +377,7 @@ 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