linux-kernel - [PATCH v2 2/2] x86/unwind/orc: Support reliable unwinding through BPF stack frames

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <a18505975662328c8ffb1090dded890c6f8c1004.1764818927.git.jpoimboe@kernel.org>
Date: Wed,  3 Dec 2025 19:32:16 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
	live-patching@...r.kernel.org,
	bpf@...r.kernel.org,
	Andrey Grodzovsky <andrey.grodzovsky@...wdstrike.com>,
	Petr Mladek <pmladek@...e.com>,
	Song Liu <song@...nel.org>,
	Raja Khan <raja.khan@...wdstrike.com>,
	Miroslav Benes <mbenes@...e.cz>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH v2 2/2] x86/unwind/orc: Support reliable unwinding through BPF stack frames

BPF JIT programs and trampolines use a frame pointer, so the current ORC
unwinder strategy of falling back to frame pointers (when an ORC entry
is missing) usually works in practice when unwinding through BPF JIT
stack frames.

However, that frame pointer fallback is just a guess, so the unwind gets
marked unreliable for live patching, which can cause livepatch
transition stalls.

Make the common case reliable by calling the bpf_has_frame_pointer()
helper to detect the valid frame pointer region of BPF JIT programs and
trampolines.

Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder")
Reported-by: Andrey Grodzovsky <andrey.grodzovsky@...wdstrike.com>
Closes: https://lore.kernel.org/0e555733-c670-4e84-b2e6-abb8b84ade38@crowdstrike.com
Acked-by: Song Liu <song@...nel.org>
Acked-and-tested-by: Andrey Grodzovsky<andrey.grodzovsky@...wdstrike.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 arch/x86/kernel/unwind_orc.c | 39 +++++++++++++++++++++++++-----------
 1 file changed, 27 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
index 977ee75e047c..f610fde2d5c4 100644
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -2,6 +2,7 @@
 #include <linux/objtool.h>
 #include <linux/module.h>
 #include <linux/sort.h>
+#include <linux/bpf.h>
 #include <asm/ptrace.h>
 #include <asm/stacktrace.h>
 #include <asm/unwind.h>
@@ -172,6 +173,25 @@ static struct orc_entry *orc_ftrace_find(unsigned long ip)
 }
 #endif
 
+/* Fake frame pointer entry -- used as a fallback for generated code */
+static struct orc_entry orc_fp_entry = {
+	.type		= ORC_TYPE_CALL,
+	.sp_reg		= ORC_REG_BP,
+	.sp_offset	= 16,
+	.bp_reg		= ORC_REG_PREV_SP,
+	.bp_offset	= -16,
+};
+
+static struct orc_entry *orc_bpf_find(unsigned long ip)
+{
+#ifdef CONFIG_BPF_JIT
+	if (bpf_has_frame_pointer(ip))
+		return &orc_fp_entry;
+#endif
+
+	return NULL;
+}
+
 /*
  * If we crash with IP==0, the last successfully executed instruction
  * was probably an indirect function call with a NULL function pointer,
@@ -186,15 +206,6 @@ static struct orc_entry null_orc_entry = {
 	.type = ORC_TYPE_CALL
 };
 
-/* Fake frame pointer entry -- used as a fallback for generated code */
-static struct orc_entry orc_fp_entry = {
-	.type		= ORC_TYPE_CALL,
-	.sp_reg		= ORC_REG_BP,
-	.sp_offset	= 16,
-	.bp_reg		= ORC_REG_PREV_SP,
-	.bp_offset	= -16,
-};
-
 static struct orc_entry *orc_find(unsigned long ip)
 {
 	static struct orc_entry *orc;
@@ -238,6 +249,11 @@ static struct orc_entry *orc_find(unsigned long ip)
 	if (orc)
 		return orc;
 
+	/* BPF lookup: */
+	orc = orc_bpf_find(ip);
+	if (orc)
+		return orc;
+
 	return orc_ftrace_find(ip);
 }
 
@@ -495,9 +511,8 @@ bool unwind_next_frame(struct unwind_state *state)
 	if (!orc) {
 		/*
 		 * As a fallback, try to assume this code uses a frame pointer.
-		 * This is useful for generated code, like BPF, which ORC
-		 * doesn't know about.  This is just a guess, so the rest of
-		 * the unwind is no longer considered reliable.
+		 * This is just a guess, so the rest of the unwind is no longer
+		 * considered reliable.
 		 */
 		orc = &orc_fp_entry;
 		state->error = true;
-- 
2.51.1