From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexei Starovoitov Subject: [PATCH bpf 4/9] bpf: fix 32-bit ALU op verification Date: Mon, 18 Dec 2017 20:11:56 -0800 Message-ID: <20171219041201.1979983-5-ast@kernel.org> References: <20171219041201.1979983-1-ast@kernel.org> Mime-Version: 1.0 Content-Type: text/plain Cc: Daniel Borkmann , Jann Horn , Edward Cree , , To: "David S . Miller" Return-path: Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:55920 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934856AbdLSEMD (ORCPT ); Mon, 18 Dec 2017 23:12:03 -0500 Received: from pps.filterd (m0044010.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id vBJ4Aaqe004778 for ; Mon, 18 Dec 2017 20:12:03 -0800 Received: from mail.thefacebook.com ([199.201.64.23]) by mx0a-00082601.pphosted.com with ESMTP id 2exnng8u62-3 (version=TLSv1 cipher=ECDHE-RSA-AES256-SHA bits=256 verify=NOT) for ; Mon, 18 Dec 2017 20:12:03 -0800 In-Reply-To: <20171219041201.1979983-1-ast@kernel.org> Sender: netdev-owner@vger.kernel.org List-ID: From: Jann Horn 32-bit ALU ops operate on 32-bit values and have 32-bit outputs. Adjust the verifier accordingly. Fixes: f1174f77b50c ("bpf/verifier: rework value tracking") Signed-off-by: Jann Horn Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 28 +++++++++++++++++----------- 1 file changed, 17 insertions(+), 11 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f716bdf29dd0..ecdc265244ca 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2017,6 +2017,10 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, return 0; } +/* WARNING: This function does calculations on 64-bit values, but the actual + * execution may occur on 32-bit values. Therefore, things like bitshifts + * need extra checks in the 32-bit case. + */ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, struct bpf_insn *insn, struct bpf_reg_state *dst_reg, @@ -2027,12 +2031,8 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, bool src_known, dst_known; s64 smin_val, smax_val; u64 umin_val, umax_val; + u64 insn_bitness = (BPF_CLASS(insn->code) == BPF_ALU64) ? 64 : 32; - if (BPF_CLASS(insn->code) != BPF_ALU64) { - /* 32-bit ALU ops are (32,32)->64 */ - coerce_reg_to_size(dst_reg, 4); - coerce_reg_to_size(&src_reg, 4); - } smin_val = src_reg.smin_value; smax_val = src_reg.smax_value; umin_val = src_reg.umin_value; @@ -2168,9 +2168,9 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, __update_reg_bounds(dst_reg); break; case BPF_LSH: - if (umax_val > 63) { - /* Shifts greater than 63 are undefined. This includes - * shifts by a negative number. + if (umax_val >= insn_bitness) { + /* Shifts greater than 31 or 63 are undefined. + * This includes shifts by a negative number. */ mark_reg_unknown(env, regs, insn->dst_reg); break; @@ -2196,9 +2196,9 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, __update_reg_bounds(dst_reg); break; case BPF_RSH: - if (umax_val > 63) { - /* Shifts greater than 63 are undefined. This includes - * shifts by a negative number. + if (umax_val >= insn_bitness) { + /* Shifts greater than 31 or 63 are undefined. + * This includes shifts by a negative number. */ mark_reg_unknown(env, regs, insn->dst_reg); break; @@ -2234,6 +2234,12 @@ static int adjust_scalar_min_max_vals(struct bpf_verifier_env *env, break; } + if (BPF_CLASS(insn->code) != BPF_ALU64) { + /* 32-bit ALU ops are (32,32)->32 */ + coerce_reg_to_size(dst_reg, 4); + coerce_reg_to_size(&src_reg, 4); + } + __reg_deduce_bounds(dst_reg); __reg_bound_offset(dst_reg); return 0; -- 2.9.5