linux-kernel - Re: [PATCH bpf-next v2 2/3] bpf: Fix aux usage after do_check

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: <34cb9cb46df58e118f7fe488ff40fd7a5cf7f224.camel@gmail.com>
Date: Sun, 29 Jun 2025 18:05:50 -0700
From: Eduard Zingerman <eddyz87@...il.com>
To: Luis Gerhorst <luis.gerhorst@....de>, Andrii Nakryiko
 <andrii@...nel.org>,  Mykola Lysenko	 <mykolal@...com>, Alexei Starovoitov
 <ast@...nel.org>, Daniel Borkmann	 <daniel@...earbox.net>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Song Liu	 <song@...nel.org>, Yonghong Song
 <yonghong.song@...ux.dev>, John Fastabend	 <john.fastabend@...il.com>, KP
 Singh <kpsingh@...nel.org>, Stanislav Fomichev	 <sdf@...ichev.me>, Hao Luo
 <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,  Shuah Khan
 <shuah@...nel.org>, Kumar Kartikeya Dwivedi <memxor@...il.com>, Peilin Ye
 <yepeilin@...gle.com>,  Jiayuan Chen	 <mrpre@....com>, Saket Kumar Bhaskar
 <skb99@...ux.ibm.com>, Ihor Solodrai	 <isolodrai@...a.com>, Daniel Xu
 <dxu@...uu.xyz>, bpf@...r.kernel.org, 	linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org, Paul Chaignon	 <paul.chaignon@...il.com>
Cc: syzbot+dc27c5fb8388e38d2d37@...kaller.appspotmail.com
Subject: Re: [PATCH bpf-next v2 2/3] bpf: Fix aux usage after do_check_insn()

On Sat, 2025-06-28 at 16:50 +0200, Luis Gerhorst wrote:

[...]

> @@ -19955,11 +19960,11 @@ static int do_check(struct bpf_verifier_env *env)
>  			/* Prevent this speculative path from ever reaching the
>  			 * insn that would have been unsafe to execute.
>  			 */
> -			cur_aux(env)->nospec = true;
> +			prev_aux(env)->nospec = true;

I don't like the prev_aux() call in this position, as one needs to
understand that after do_check_insn() call what was current became
previous. This at-least requires a comment. Implementation with a
temporary variable (as at the bottom of this email), imo, is less
cognitive load.

>  			/* IF it was an ADD/SUB insn, potentially remove any
>  			 * markings for alu sanitization.
>  			 */
> -			cur_aux(env)->alu_state = 0;
> +			prev_aux(env)->alu_state = 0;
>  			goto process_bpf_exit;
>  		} else if (err < 0) {
>  			return err;

[...]

---

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a136d9b1b25f..a923614b7104 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -19953,6 +19953,7 @@ static 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;
 	struct bpf_insn *insns = env->prog->insnsi;
+	struct bpf_insn_aux_data *insn_aux;
 	int insn_cnt = env->prog->len;
 	bool do_print_state = false;
 	int prev_insn_idx = -1;
@@ -19972,6 +19973,7 @@ static int do_check(struct bpf_verifier_env *env)
 		}
 
 		insn = &insns[env->insn_idx];
+		insn_aux = &env->insn_aux_data[env->insn_idx];
 
 		if (++env->insn_processed > BPF_COMPLEXITY_LIMIT_INSNS) {
 			verbose(env,
@@ -20048,7 +20050,7 @@ static int do_check(struct bpf_verifier_env *env)
 		/* Reduce verification complexity by stopping speculative path
 		 * verification when a nospec is encountered.
 		 */
-		if (state->speculative && cur_aux(env)->nospec)
+		if (state->speculative && insn_aux->nospec)
 			goto process_bpf_exit;
 
 		err = do_check_insn(env, &do_print_state);
@@ -20056,11 +20058,11 @@ static int do_check(struct bpf_verifier_env *env)
 			/* Prevent this speculative path from ever reaching the
 			 * insn that would have been unsafe to execute.
 			 */
-			cur_aux(env)->nospec = true;
+			insn_aux->nospec = true;
 			/* If it was an ADD/SUB insn, potentially remove any
 			 * markings for alu sanitization.
 			 */
-			cur_aux(env)->alu_state = 0;
+			insn_aux->alu_state = 0;
 			goto process_bpf_exit;
 		} else if (err < 0) {
 			return err;
@@ -20069,7 +20071,7 @@ static int do_check(struct bpf_verifier_env *env)
 		}
 		WARN_ON_ONCE(err);
 
-		if (state->speculative && cur_aux(env)->nospec_result) {
+		if (state->speculative && insn_aux->nospec_result) {
 			/* If we are on a path that performed a jump-op, this
 			 * may skip a nospec patched-in after the jump. This can
 			 * currently never happen because nospec_result is only