From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EE2DFC43381 for ; Fri, 1 Mar 2019 23:23:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C3A4A205F4 for ; Fri, 1 Mar 2019 23:23:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725996AbfCAXXC (ORCPT ); Fri, 1 Mar 2019 18:23:02 -0500 Received: from www62.your-server.de ([213.133.104.62]:34198 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725958AbfCAXXC (ORCPT ); Fri, 1 Mar 2019 18:23:02 -0500 Received: from [78.46.172.2] (helo=sslproxy05.your-server.de) by www62.your-server.de with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89_1) (envelope-from ) id 1gzrUZ-0005zh-Oy; Sat, 02 Mar 2019 00:22:59 +0100 Received: from [178.197.248.21] (helo=linux.home) by sslproxy05.your-server.de with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89) (envelope-from ) id 1gzrUZ-000ALw-J5; Sat, 02 Mar 2019 00:22:59 +0100 Subject: Re: [PATCH bpf] bpf: fix sanitation rewrite in case of non-pointers To: Song Liu Cc: Alexei Starovoitov , afabre@cloudflare.com, Marek Majkowski , bpf@vger.kernel.org, Networking References: <20190301210529.8218-1-daniel@iogearbox.net> From: Daniel Borkmann Message-ID: Date: Sat, 2 Mar 2019 00:22:59 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.100.2/25374/Thu Feb 28 11:38:05 2019) Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 03/02/2019 12:18 AM, Song Liu wrote: > On Fri, Mar 1, 2019 at 1:06 PM Daniel Borkmann wrote: >> >> Marek reported that he saw an issue with the below snippet in that >> timing measurements where off when loaded as unpriv while results >> were reasonable when loaded as privileged: >> >> [...] >> uint64_t a = bpf_ktime_get_ns(); >> uint64_t b = bpf_ktime_get_ns(); >> uint64_t delta = b - a; >> if ((int64_t)delta > 0) { >> [...] >> >> Turns out there is a bug where a corner case is missing in the fix >> d3bd7413e0ca ("bpf: fix sanitation of alu op with pointer / scalar >> type from different paths"), namely fixup_bpf_calls() only checks >> whether aux has a non-zero alu_state, but it also needs to test for >> the case of BPF_ALU_NON_POINTER since in both occasions we need to >> skip the masking rewrite (as there is nothing to mask). >> >> Fixes: d3bd7413e0ca ("bpf: fix sanitation of alu op with pointer / scalar type from different paths") >> Reported-by: Marek Majkowski >> Reported-by: Arthur Fabre >> Signed-off-by: Daniel Borkmann >> Link: https://lore.kernel.org/netdev/CAJPywTJqP34cK20iLM5YmUMz9KXQOdu1-+BZrGMAGgLuBWz7fg@mail.gmail.com/T/ >> --- >> [ Test case will be routed via bpf-next to avoid useless merge churn >> due to test_verifier rework in bpf-next. ] >> >> kernel/bpf/verifier.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c >> index 8f295b790297..5fcce2f4209d 100644 >> --- a/kernel/bpf/verifier.c >> +++ b/kernel/bpf/verifier.c >> @@ -6920,7 +6920,8 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env) >> u32 off_reg; >> >> aux = &env->insn_aux_data[i + delta]; >> - if (!aux->alu_state) >> + if (!aux->alu_state || >> + aux->alu_state == BPF_ALU_NON_POINTER) > > alu_state is a bitmap. Shall we check "aux->alu_state & > BPF_ALU_NON_POINTER" here? The state in this case can only ever be BPF_ALU_NON_POINTER, any other setting from sanitize_val_alu() would be a violation.