From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3B8032571D7; Mon, 27 Oct 2025 13:14:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761570866; cv=none; b=ogUZjFlR5sla2ECr/WRkBed+D+7TG/qhMRosUpoSD519tClcbcNSPw1WwwemrwZmC31M7GJo4HS127A4dj5gY2rzHfLrkknIpB76IesqjVDwI8iyM4dPAnMn0i9N7NX+HPNIEBxZI2Bx1LQnYcnl7GscsMRgMKLULKHKta16mL4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761570866; c=relaxed/simple; bh=Fz1tu0mzcidGzthNvqcB+rfBjYZ08d3OyGUaWr8e94w=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=VgWszHNj8zDpu2J3DAM6M/+5Z7cLFE15jjoMt8MJPa9DINV5Ps5dNZuXqcp/NyTttNPv2urk1sGwxxzSOQHCofYqRI8Ubi0fy7ZIrCOmsgysK9ew/8KBPXn9FaIn/0jkTNjzlPKw7MM7rgB8ekBq+Icjd6u0TELKWGqtnqoK2sM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Z+Octpgg; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Z+Octpgg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5F646C4CEF1; Mon, 27 Oct 2025 13:14:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1761570865; bh=Fz1tu0mzcidGzthNvqcB+rfBjYZ08d3OyGUaWr8e94w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Z+OctpggykHXh937o/Bs3bFENJBoZbBeLvhBwdACqNoSQc9E6S9elqWFefAOn3IY6 YmcSmKRpHs+duwqY3wRdcv0OjCYJQ+9sAsKgw7Qjmp6ShXikWBJTqUT1Tfy8vhiRSS 3y8lzJBK8/dtTY7/8D2/DIoMUvaw8VGPy3Zs1ZlpEoAZs3jhYdYoMhlvMTNXo5YJH/ HPXKmjIPtsCqwEZof7RWi8TLt/yEO+tLYKPr958rmG1yWevC3lZ9+7uSi9AE2cpQ38 CYmY4QB/V7sCVCuKN0fvj6fLP9pRajXwvnvXnn7j/n6QmH+haDaFyQfEoMBdidPaZA QQ+APffGf1sFA== From: Jiri Olsa To: Masami Hiramatsu , Steven Rostedt , Josh Poimboeuf Cc: Peter Zijlstra , bpf@vger.kernel.org, linux-trace-kernel@vger.kernel.org, x86@kernel.org, Yonghong Song , Song Liu , Andrii Nakryiko Subject: [PATCH 2/3] x86/fgraph,bpf: Fix stack ORC unwind from kprobe_multi return probe Date: Mon, 27 Oct 2025 14:13:53 +0100 Message-ID: <20251027131354.1984006-3-jolsa@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251027131354.1984006-1-jolsa@kernel.org> References: <20251027131354.1984006-1-jolsa@kernel.org> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 Note I feel like it'd be better to set those directly in return_to_handler, but Steven suggested setting them later in kprobe_multi code path. Signed-off-by: Jiri Olsa --- 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 93156ac4ffe0..b08c95872eed 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 367da3638167..823dbdd0eb41 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 7ded7df6e9b5..07f8c309e432 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 */ -- 2.51.0