linux-kernel - [PATCH] bpf: turn off sanitizer in do_misc

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Message-Id: <20250620113846.3950478-1-arnd@kernel.org>
Date: Fri, 20 Jun 2025 13:38:31 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>
Cc: Arnd Bergmann <arnd@...db.de>,
	John Fastabend <john.fastabend@...il.com>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Kumar Kartikeya Dwivedi <memxor@...il.com>,
	Luis Gerhorst <luis.gerhorst@....de>,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: [PATCH] bpf: turn off sanitizer in do_misc_fixups for old clang

From: Arnd Bergmann <arnd@...db.de>

clang versions before version 18 manage to badly optimize the bpf
verifier, with lots of variable spills leading to excessive stack
usage in addition to likely rather slow code:

kernel/bpf/verifier.c:23936:5: error: stack frame size (2096) exceeds limit (1280) in 'bpf_check' [-Werror,-Wframe-larger-than]
kernel/bpf/verifier.c:21563:12: error: stack frame size (1984) exceeds limit (1280) in 'do_misc_fixups' [-Werror,-Wframe-larger-than]

Turn off the sanitizer in the two functions that suffer the most from
this when using one of the affected clang version.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 kernel/bpf/verifier.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2fa797a6d6a2..7724c7a56d79 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -19810,7 +19810,14 @@ static int do_check_insn(struct bpf_verifier_env *env, bool *do_print_state)
 	return 0;
 }
 
-static int do_check(struct bpf_verifier_env *env)
+#if defined(CONFIG_CC_IS_CLANG) && CONFIG_CLANG_VERSION < 180100
+/* old clang versions cause excessive stack usage here */
+#define __workaround_kasan  __disable_sanitizer_instrumentation
+#else
+#define __workaround_kasan
+#endif
+
+static __workaround_kasan int do_check(struct bpf_verifier_env *env)
 {
 	bool pop_log = !(env->log.level & BPF_LOG_LEVEL2);
 	struct bpf_verifier_state *state = env->cur_state;
@@ -21817,7 +21824,7 @@ static int add_hidden_subprog(struct bpf_verifier_env *env, struct bpf_insn *pat
 /* Do various post-verification rewrites in a single program pass.
  * These rewrites simplify JIT and interpreter implementations.
  */
-static int do_misc_fixups(struct bpf_verifier_env *env)
+static __workaround_kasan int do_misc_fixups(struct bpf_verifier_env *env)
 {
 	struct bpf_prog *prog = env->prog;
 	enum bpf_attach_type eatype = prog->expected_attach_type;
-- 
2.39.5