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x86/fgraph,bpf: Fix stack ORC unwind from kprobe_multi return probe

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Currently we don't get stack trace via ORC unwinder on top of fgraph exit
handler. We can see that when generating stacktrace from kretprobe_multi
bpf program which is based on fprobe/fgraph.

The reason is that the ORC unwind code won't get pass the return_to_handler
callback installed by fgraph return probe machinery.

Solving this by creating stack frame in return_to_handler expected by
ftrace_graph_ret_addr function to recover original return address and
continue with the unwind.

Also updating the pt_regs data with cs/flags/rsp which are needed for
successful stack retrieval from ebpf bpf_get_stackid helper.
 - in get_perf_callchain we check user_mode(regs) so CS has to be set
 - in perf_callchain_kernel we call perf_hw_regs(regs), so EFLAGS/FIXED
    has to be unset

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20251104215405.168643-3-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Jiri Olsa
2025-11-04 22:54:03 +01:00
committed by Alexei Starovoitov
parent 6d08340d1e
commit 20a0bc1027
3 changed files with 21 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
arch/x86/include/asm/ftrace.h
View File

@@ -56,6 +56,11 @@ arch_ftrace_get_regs(struct ftrace_regs *fregs)
return &arch_ftrace_regs(fregs)->regs;
}
#define arch_ftrace_partial_regs(regs) do { \
regs->flags &= ~X86_EFLAGS_FIXED; \
regs->cs = __KERNEL_CS; \
} while (0)
#define arch_ftrace_fill_perf_regs(fregs, _regs) do { \
(_regs)->ip = arch_ftrace_regs(fregs)->regs.ip; \
(_regs)->sp = arch_ftrace_regs(fregs)->regs.sp; \

8
arch/x86/kernel/ftrace_64.S
View File

@@ -354,12 +354,17 @@ SYM_CODE_START(return_to_handler)
UNWIND_HINT_UNDEFINED
ANNOTATE_NOENDBR
/* Restore return_to_handler value that got eaten by previous ret instruction. */
subq $8, %rsp
UNWIND_HINT_FUNC
/* Save ftrace_regs for function exit context */
subq $(FRAME_SIZE), %rsp
movq %rax, RAX(%rsp)
movq %rdx, RDX(%rsp)
movq %rbp, RBP(%rsp)
movq %rsp, RSP(%rsp)
movq %rsp, %rdi
call ftrace_return_to_handler
@@ -368,7 +373,8 @@ SYM_CODE_START(return_to_handler)
movq RDX(%rsp), %rdx
movq RAX(%rsp), %rax
addq $(FRAME_SIZE), %rsp
addq $(FRAME_SIZE) + 8, %rsp
/*
* Jump back to the old return address. This cannot be JMP_NOSPEC rdi
* since IBT would demand that contain ENDBR, which simply isn't so for

10
include/linux/ftrace.h
View File

@@ -193,6 +193,10 @@ static __always_inline struct pt_regs *ftrace_get_regs(struct ftrace_regs *fregs
#if !defined(CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS) || \
defined(CONFIG_HAVE_FTRACE_REGS_HAVING_PT_REGS)
#ifndef arch_ftrace_partial_regs
#define arch_ftrace_partial_regs(regs) do {} while (0)
#endif
static __always_inline struct pt_regs *
ftrace_partial_regs(struct ftrace_regs *fregs, struct pt_regs *regs)
{
@@ -202,7 +206,11 @@ ftrace_partial_regs(struct ftrace_regs *fregs, struct pt_regs *regs)
* Since arch_ftrace_get_regs() will check some members and may return
* NULL, we can not use it.
*/
return &arch_ftrace_regs(fregs)->regs;
regs = &arch_ftrace_regs(fregs)->regs;
/* Allow arch specific updates to regs. */
arch_ftrace_partial_regs(regs);
return regs;
}
#endif /* !CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS || CONFIG_HAVE_FTRACE_REGS_HAVING_PT_REGS */