From nobody Sun Feb 8 08:22:23 2026 Received: from out-178.mta1.migadu.com (out-178.mta1.migadu.com [95.215.58.178]) (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 45921273809 for ; Sat, 25 Oct 2025 05:31:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.178 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761370297; cv=none; b=ZBRNuUNHf4+akuY49h1VYOpseHJ6aho3DlCQOSfQTlzZZPKSsqlnaZKjnqhv2dWubwtAl3+XMHEiFvD783jWWn7QNOeYbmdxNHHX4Yxv+w2ZUf9jHR1ABcL6oVuPHgIAgQ/sJ/NP+7ROweXY99dmCgpc0xLV/a5qHlABDrDj74I= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761370297; c=relaxed/simple; bh=dioH+7hCvMyS5Tx1o3rs6buZVgj948rfxHcInzZDHh8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=EfC6CSryELTo5sodP5qC3gw4wDRHhz0oaFABOvB6dYjUO8i2jiNjzEV+jBiInRqZPU8Vq2mjJ1bbEkiK/JcQmMiY+V7gdL1eBQoMBTIreEzG1VVODSLwMlK3PZ5jyb+kvEZ4PBtO/hV2kIT5EQOwiAOAUghaRvt459SBwuniYew= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=enxORHHk; arc=none smtp.client-ip=95.215.58.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="enxORHHk" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1761370293; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=m13+M6D1mpmzJOilgH7TsH0yLWlIw5RngITMJiFHo+w=; b=enxORHHkmdFXXulr3CKhA2OIrlI1o9qxDprov9m4P2N0+Rvb9GSQKq9lR0ynbr05zbUZZn 6bBRjPw/yNIr3F0NQ2yBFbhY3GTQE46OFN0/+pWUqox7/Uqw6CBSHWzHMOgw4d7+H9LR4H z2pp/W5X1Z2ktwk1v1aAAJFqd5bn344= From: KaFai Wan To: ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, shuah@kernel.org, paul.chaignon@gmail.com, m.shachnai@gmail.com, harishankar.vishwanathan@gmail.com, colin.i.king@gmail.com, luis.gerhorst@fau.de, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: KaFai Wan , Kaiyan Mei , Yinhao Hu Subject: [PATCH bpf-next v2 1/2] bpf: Skip bounds adjustment for conditional jumps on same register Date: Sat, 25 Oct 2025 13:30:16 +0800 Message-ID: <20251025053017.2308823-2-kafai.wan@linux.dev> In-Reply-To: <20251025053017.2308823-1-kafai.wan@linux.dev> References: <20251025053017.2308823-1-kafai.wan@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset="utf-8" When conditional jumps are performed on the same register (e.g., r0 <=3D r0, r0 > r0, r0 < r0) where the register holds a scalar with range, the verifier incorrectly attempts to adjust the register's min/max bounds. This leads to invalid range bounds and triggers a BUG warning: verifier bug: REG INVARIANTS VIOLATION (true_reg1): range bounds violation = u64=3D[0x1, 0x0] s64=3D[0x1, 0x0] u32=3D[0x1, 0x0] s32=3D[0x1, 0x0] var_off= =3D(0x0, 0x0) WARNING: CPU: 0 PID: 92 at kernel/bpf/verifier.c:2731 reg_bounds_sanity_che= ck+0x163/0x220 Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 1.16.3-debi= an-1.16.3-2 04/01/2014 RIP: 0010:reg_bounds_sanity_check+0x163/0x220 Call Trace: reg_set_min_max+0xf7/0x1d0 check_cond_jmp_op+0x57b/0x1730 ? print_bpf_insn+0x3d5/0xa50 do_check_common+0x33ac/0x33c0 ... The root cause is in regs_refine_cond_op() where BPF_JLT/BPF_JSLT operations adjust both min/max bounds on the same register, causing invalid bounds. Since comparing a register with itself should not change its bounds (the comparison result is always known: r0 =3D=3D r0 is always true, r0 < r0 is always false), the bounds adjustment is unnecessary. Fix this by: 1. Enhance is_branch_taken() and is_scalar_branch_taken() to properly handle branch direction computation for same register comparisons across all BPF jump operations 2. For unknown branch directions (e.g., BPF_JSET), add early return in reg_set_min_max() to avoid bounds adjustment on the same register The fix ensures that unnecessary bounds adjustments are skipped, preventing the verifier bug while maintaining correct branch direction analysis. Reported-by: Kaiyan Mei Reported-by: Yinhao Hu Closes: https://lore.kernel.org/all/1881f0f5.300df.199f2576a01.Coremail.kai= yanm@hust.edu.cn/ Fixes: 0df1a55afa83 ("bpf: Warn on internal verifier errors") Signed-off-by: KaFai Wan --- kernel/bpf/verifier.c | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 6d175849e57a..653fa96ed0df 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -16037,6 +16037,12 @@ static int is_scalar_branch_taken(struct bpf_reg_s= tate *reg1, struct bpf_reg_sta } break; case BPF_JSET: + if (reg1 =3D=3D reg2) { + if (tnum_is_const(t1)) + return t1.value !=3D 0; + else + return (smin1 <=3D 0 && smax1 >=3D 0) ? -1 : 1; + } if (!is_reg_const(reg2, is_jmp32)) { swap(reg1, reg2); swap(t1, t2); @@ -16172,6 +16178,25 @@ static int is_pkt_ptr_branch_taken(struct bpf_reg_= state *dst_reg, static int is_branch_taken(struct bpf_reg_state *reg1, struct bpf_reg_stat= e *reg2, u8 opcode, bool is_jmp32) { + if (reg1 =3D=3D reg2) { + switch (opcode) { + case BPF_JGE: + case BPF_JLE: + case BPF_JSGE: + case BPF_JSLE: + case BPF_JEQ: + return 1; + case BPF_JGT: + case BPF_JLT: + case BPF_JSGT: + case BPF_JSLT: + case BPF_JNE: + return 0; + default: + break; + } + } + if (reg_is_pkt_pointer_any(reg1) && reg_is_pkt_pointer_any(reg2) && !is_j= mp32) return is_pkt_ptr_branch_taken(reg1, reg2, opcode); =20 @@ -16429,6 +16454,13 @@ static int reg_set_min_max(struct bpf_verifier_env= *env, if (false_reg1->type !=3D SCALAR_VALUE || false_reg2->type !=3D SCALAR_VA= LUE) return 0; =20 + /* We compute branch direction for same registers in is_branch_taken() and + * is_scalar_branch_taken(). For unknown branch directions (e.g., BPF_JSE= T) + * on the same registers, we don't need to adjusts the min/max values. + */ + if (false_reg1 =3D=3D false_reg2) + return 0; + /* fallthrough (FALSE) branch */ regs_refine_cond_op(false_reg1, false_reg2, rev_opcode(opcode), is_jmp32); reg_bounds_sync(false_reg1); --=20 2.43.0