From 20a0bc10272fa17a44fc857c31574a8306f60d20 Mon Sep 17 00:00:00 2001 From: Jiri Olsa Date: Tue, 4 Nov 2025 22:54:03 +0100 Subject: [PATCH] x86/fgraph,bpf: Fix stack ORC unwind from kprobe_multi return probe 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) Signed-off-by: Jiri Olsa Link: https://lore.kernel.org/r/20251104215405.168643-3-jolsa@kernel.org Signed-off-by: Alexei Starovoitov Acked-by: Steven Rostedt (Google) --- arch/x86/include/asm/ftrace.h | 5 +++++ arch/x86/kernel/ftrace_64.S | 8 +++++++- include/linux/ftrace.h | 10 +++++++++- 3 files changed, 21 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h index 93156ac4ffe09..b08c95872eed9 100644 --- a/arch/x86/include/asm/ftrace.h +++ b/arch/x86/include/asm/ftrace.h @@ -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; \ diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S index 367da36381678..823dbdd0eb410 100644 --- a/arch/x86/kernel/ftrace_64.S +++ b/arch/x86/kernel/ftrace_64.S @@ -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 diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h index 7ded7df6e9b50..07f8c309e4327 100644 --- a/include/linux/ftrace.h +++ b/include/linux/ftrace.h @@ -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 */ -- 2.47.3