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[2a01:cb08:8949:7e00:b67e:3b46:11bd:9a64]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45382363f7fsm26917285e9.27.2025.06.25.11.01.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Jun 2025 11:01:44 -0700 (PDT) Date: Wed, 25 Jun 2025 20:01:41 +0200 From: Paul Chaignon To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Luis Gerhorst Subject: [PATCH bpf-next] bpf: Fix unwarranted warning on speculative path Message-ID: Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Commit d6f1c85f2253 ("bpf: Fall back to nospec for Spectre v1") added a WARN_ON_ONCE to check that we're not skipping a nospec due to a jump. It however failed to take into account LDIMM64 instructions as below: 15: (18) r1 = 0x2020200005642020 17: (7b) *(u64 *)(r10 -264) = r1 This bytecode snippet generates a warning because the move from the LDIMM64 instruction to the next instruction is seen as a jump. This patch fixes it. Reported-by: syzbot+dc27c5fb8388e38d2d37@syzkaller.appspotmail.com Fixes: d6f1c85f2253 ("bpf: Fall back to nospec for Spectre v1") Signed-off-by: Paul Chaignon --- kernel/bpf/verifier.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 279a64933262..66841ed6dfc0 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -19819,6 +19819,7 @@ static int do_check(struct bpf_verifier_env *env) int insn_cnt = env->prog->len; bool do_print_state = false; int prev_insn_idx = -1; + int insn_sz; for (;;) { struct bpf_insn *insn; @@ -19942,7 +19943,8 @@ static int do_check(struct bpf_verifier_env *env) * to document this in case nospec_result is used * elsewhere in the future. */ - WARN_ON_ONCE(env->insn_idx != prev_insn_idx + 1); + insn_sz = bpf_is_ldimm64(insn) ? 2 : 1; + WARN_ON_ONCE(env->insn_idx != prev_insn_idx + insn_sz); process_bpf_exit: mark_verifier_state_scratched(env); err = update_branch_counts(env, env->cur_state); -- 2.43.0