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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 70D66C433DF for ; Wed, 1 Jul 2020 09:17:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4B26520722 for ; Wed, 1 Jul 2020 09:17:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728784AbgGAJRa (ORCPT ); Wed, 1 Jul 2020 05:17:30 -0400 Received: from www62.your-server.de ([213.133.104.62]:51128 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728776AbgGAJR3 (ORCPT ); Wed, 1 Jul 2020 05:17:29 -0400 Received: from sslproxy02.your-server.de ([78.47.166.47]) by www62.your-server.de with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89_1) (envelope-from ) id 1jqYrp-0004Of-Sz; Wed, 01 Jul 2020 11:17:21 +0200 Received: from [178.196.57.75] (helo=pc-9.home) by sslproxy02.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1jqYrp-000Gex-LM; Wed, 01 Jul 2020 11:17:21 +0200 Subject: Re: [PATCH v5 bpf-next 2/5] bpf: Introduce sleepable BPF programs To: Alexei Starovoitov Cc: davem@davemloft.net, paulmck@kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, kernel-team@fb.com References: <20200630043343.53195-1-alexei.starovoitov@gmail.com> <20200630043343.53195-3-alexei.starovoitov@gmail.com> <20200630234117.arqmjpbivy5fhhmk@ast-mbp.dhcp.thefacebook.com> From: Daniel Borkmann Message-ID: <1e9d88c9-c5f2-6def-7afc-aca47a88f4b0@iogearbox.net> Date: Wed, 1 Jul 2020 11:17:21 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20200630234117.arqmjpbivy5fhhmk@ast-mbp.dhcp.thefacebook.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.102.3/25859/Tue Jun 30 15:38:05 2020) Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 7/1/20 1:41 AM, Alexei Starovoitov wrote: > On Wed, Jul 01, 2020 at 01:26:44AM +0200, Daniel Borkmann wrote: >> On 6/30/20 6:33 AM, Alexei Starovoitov wrote: >> [...] >>> +/* list of non-sleepable kernel functions that are otherwise >>> + * available to attach by bpf_lsm or fmod_ret progs. >>> + */ >>> +static int check_sleepable_blacklist(unsigned long addr) >>> +{ >>> +#ifdef CONFIG_BPF_LSM >>> + if (addr == (long)bpf_lsm_task_free) >>> + return -EINVAL; >>> +#endif >>> +#ifdef CONFIG_SECURITY >>> + if (addr == (long)security_task_free) >>> + return -EINVAL; >>> +#endif >>> + return 0; >>> +} >> >> Would be nice to have some sort of generic function annotation to describe >> that code cannot sleep inside of it, and then filter based on that. Anyway, >> is above from manual code inspection? > > yep. all manual. I don't think there is a way to automate it. > At least I cannot think of one. Automation might be hard, but maybe semi-automate: we have a cant_migrate() assertion in __BPF_PROG_RUN() which asserts on cant_sleep() PREEMPT_RT kernels at least. We originally just has the cant_sleep() there before 37e1d9202225 ("bpf: Replace cant_sleep() with cant_migrate()"). So perhaps one way to catch bugs for sleepable progs is to add a __might_sleep() into __bpf_prog_enter_sleepable() in order to trigger the assertion generally for DEBUG_ATOMIC_SLEEP configured kernels when we're in non-sleepable sections? Still not perfect since the code needs to be exercised first but better than nothing at all. >> What about others like security_sock_rcv_skb() for example which could be >> bh_lock_sock()'ed (or, generally hooks running in softirq context)? > > ahh. it's in running in bh at that point? then it should be added to blacklist. Yep. Thanks, Daniel