From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexei Starovoitov Subject: [PATCH bpf 6/9] bpf: force strict alignment checks for stack pointers Date: Mon, 18 Dec 2017 20:11:58 -0800 Message-ID: <20171219041201.1979983-7-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]:57894 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S936226AbdLSEMD (ORCPT ); Mon, 18 Dec 2017 23:12:03 -0500 Received: from pps.filterd (m0109333.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id vBJ4AQg1031846 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 2exnjnrurt-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 Force strict alignment checks for stack pointers because the tracking of stack spills relies on it; unaligned stack accesses can lead to corruption of spilled registers, which is exploitable. Fixes: f1174f77b50c ("bpf/verifier: rework value tracking") Signed-off-by: Jann Horn Signed-off-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 77e4b5223867..102c519836f6 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1059,6 +1059,11 @@ static int check_ptr_alignment(struct bpf_verifier_env *env, break; case PTR_TO_STACK: pointer_desc = "stack "; + /* The stack spill tracking logic in check_stack_write() + * and check_stack_read() relies on stack accesses being + * aligned. + */ + strict = true; break; default: break; -- 2.9.5