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=-5.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, 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 2176EC47082 for ; Wed, 26 May 2021 17:15:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 04847613BE for ; Wed, 26 May 2021 17:15:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234265AbhEZRQ7 (ORCPT ); Wed, 26 May 2021 13:16:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43094 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234233AbhEZRQ6 (ORCPT ); Wed, 26 May 2021 13:16:58 -0400 Received: from mail-il1-x12f.google.com (mail-il1-x12f.google.com [IPv6:2607:f8b0:4864:20::12f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 14FF8C061756 for ; Wed, 26 May 2021 10:15:27 -0700 (PDT) Received: by mail-il1-x12f.google.com with SMTP id k4so1581827ili.4 for ; Wed, 26 May 2021 10:15:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=aYKMuSKZVVdni+NfNKkXv3BlEOKam17qC1VvXW9yFpQ=; b=a79j6AZMQTm+qQYGqVhkjMfcARroJ37lEZmgKGSigQBNpJHMY+kK9LW9RAn4voppaq XtqQNIQWw7a2tOKPDT4Mxt6E335/aEB7eO0w6OPzc2J6+6K2PBWJbCLCXX+nDNmMl7YF roHuhUXs9sl/DW+BRZ2GlTgnlGrgqfsmRi+s6jBud8GGbh0Z4xeLMSRgr8r2Lj+RhRnn gsnnvEedrEEqBoAI4iERcpp90OL3eX+lTL6c5MRkP8Iy355puOTWM1/yPL07wsR4nyNf iWkW5CFUozrq9C5DWCO5OxmfT95+mTuym2psTB5xtsMze3LPCoLEU/s519mp8zc9pqlj nnzw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=aYKMuSKZVVdni+NfNKkXv3BlEOKam17qC1VvXW9yFpQ=; b=gvyKy2qFAEbXsi51GuAHIdD81md2lF69kaUsL4JHVD/aDSPdGGgAyiXkpZEu4nX+z8 iyvb86t41jBrz6sd01Ni5V6GLnY50Pm9PVhMFvOJ62JJ4dBvEu80WSwKFYS2SpZAo5bo nl08ZihQnrJZWi5WGd6hzxRtFy2FT96y9e7NbFEQHrSsNhrJ93QaNHgF7fnVbRy7TUu6 rhLHWN6x3Wjs08ga+3xMpQc8iTtRRTGhEAJCj0b3/jZKjYdJ1mYVOvY8rJtOXZars87N Vw6H4SXdED9XpjLXekXO+zKqPhOz+aIuwtNQ1IGrbfdLxiulLnwk45zNNF9uu6NhbEKW QACA== X-Gm-Message-State: AOAM533BJ5tOQFxaOUnBYS0fIj6OnMNy1p39zx07JYKQpWY4tQldKBMf /yhsX/zcBcRJHLMQzr8wE/wIbg== X-Google-Smtp-Source: ABdhPJziYu08DO0Qp7L+9EYTQPjE1ppNL7H8P/SYVnqtm1MiORyY5E/g7M4RCyWBvbIGB5hTfGUucA== X-Received: by 2002:a92:d24d:: with SMTP id v13mr27737100ilg.174.1622049326279; Wed, 26 May 2021 10:15:26 -0700 (PDT) Received: from [192.168.1.30] ([65.144.74.34]) by smtp.gmail.com with ESMTPSA id c11sm15132793ilo.61.2021.05.26.10.15.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 26 May 2021 10:15:25 -0700 (PDT) Subject: Re: [RFC PATCH 2/9] audit,io_uring,io-wq: add some basic audit support to io_uring To: Paul Moore Cc: Pavel Begunkov , linux-security-module@vger.kernel.org, selinux@vger.kernel.org, linux-audit@redhat.com, io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, Kumar Kartikeya Dwivedi , Alexander Viro References: <162163367115.8379.8459012634106035341.stgit@sifl> <162163379461.8379.9691291608621179559.stgit@sifl> <162219f9-7844-0c78-388f-9b5c06557d06@gmail.com> <8943629d-3c69-3529-ca79-d7f8e2c60c16@kernel.dk> From: Jens Axboe Message-ID: <9e69e4b6-2b87-a688-d604-c7f70be894f5@kernel.dk> Date: Wed, 26 May 2021 11:15:24 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: On 5/25/21 8:04 PM, Paul Moore wrote: > On Tue, May 25, 2021 at 9:11 PM Jens Axboe wrote: >> On 5/24/21 1:59 PM, Paul Moore wrote: >>> That said, audit is not for everyone, and we have build time and >>> runtime options to help make life easier. Beyond simply disabling >>> audit at compile time a number of Linux distributions effectively >>> shortcut audit at runtime by adding a "never" rule to the audit >>> filter, for example: >>> >>> % auditctl -a task,never >> >> As has been brought up, the issue we're facing is that distros have >> CONFIG_AUDIT=y and hence the above is the best real world case outside >> of people doing custom kernels. My question would then be how much >> overhead the above will add, considering it's an entry/exit call per op. >> If auditctl is turned off, what is the expectation in turns of overhead? > > I commented on that case in my last email to Pavel, but I'll try to go > over it again in a little more detail. > > As we discussed earlier in this thread, we can skip the req->opcode > check before both the _entry and _exit calls, so we are left with just > the bare audit calls in the io_uring code. As the _entry and _exit > functions are small, I've copied them and their supporting functions > below and I'll try to explain what would happen in CONFIG_AUDIT=y, > "task,never" case. > > + static inline struct audit_context *audit_context(void) > + { > + return current->audit_context; > + } > > + static inline bool audit_dummy_context(void) > + { > + void *p = audit_context(); > + return !p || *(int *)p; > + } > > + static inline void audit_uring_entry(u8 op) > + { > + if (unlikely(audit_enabled && audit_context())) > + __audit_uring_entry(op); > + } > > We have one if statement where the conditional checks on two > individual conditions. The first (audit_enabled) is simply a check to > see if anyone has "turned on" auditing at runtime; historically this > worked rather well, and still does in a number of places, but ever > since systemd has taken to forcing audit on regardless of the admin's > audit configuration it is less useful. The second (audit_context()) > is a check to see if an audit_context has been allocated for the > current task. In the case of "task,never" current->audit_context will > be NULL (see audit_alloc()) and the __audit_uring_entry() slowpath > will never be called. > > Worst case here is checking the value of audit_enabled and > current->audit_context. Depending on which you think is more likely > we can change the order of the check so that the > current->audit_context check is first if you feel that is more likely > to be NULL than audit_enabled is to be false (it may be that way now). > > + static inline void audit_uring_exit(int success, long code) > + { > + if (unlikely(!audit_dummy_context())) > + __audit_uring_exit(success, code); > + } > > The exit call is very similar to the entry call, but in the > "task,never" case it is very simple as the first check to be performed > is the current->audit_context check which we know to be NULL. The > __audit_uring_exit() slowpath will never be called. I actually ran some numbers this morning. The test base is 5.13+, and CONFIG_AUDIT=y and CONFIG_AUDITSYSCALL=y is set for both the baseline test and the test with this series applied. I used your git branch as of this morning. The test case is my usual peak perf test, which is random reads at QD=128 and using polled IO. It's a single core test, not threaded. I ran two different tests - one was having a thread just do the IO, the other is using SQPOLL to do the IO for us. The device is capable than more IOPS than a single core can deliver, so we're CPU limited in this test. Hence it's a good test case as it does actual work, and shows software overhead quite nicely. Runs are very stable (less than 0.5% difference between runs on the same base), yet I did average 4 runs. Kernel SQPOLL IOPS Perf diff --------------------------------------------------------- 5.13 0 3029872 0.0% 5.13 1 3031056 0.0% 5.13 + audit 0 2894160 -4.5% 5.13 + audit 1 2886168 -4.8% That's an immediate drop in perf of almost 5%. Looking at a quick profile of it (nothing fancy, just checking for 'audit' in the profile) shows this: + 2.17% io_uring [kernel.vmlinux] [k] __audit_uring_entry + 0.71% io_uring [kernel.vmlinux] [k] __audit_uring_exit 0.07% io_uring [kernel.vmlinux] [k] __audit_syscall_entry 0.02% io_uring [kernel.vmlinux] [k] __audit_syscall_exit Note that this is with _no_ rules! >> aio never had any audit logging as far as I can tell. I think it'd make >> a lot more sense to selectively enable audit logging only for opcodes >> that we care about. File open/create/unlink/mkdir etc, that kind of >> thing. File level operations that people would care about logging. Would >> they care about logging a buffer registration or a polled read from a >> device/file? I highly doubt it, and we don't do that for alternative >> methods either. Doesn't really make sense for a lot of the other >> operations, imho. > > We would need to check with the current security requirements (there > are distro people on the linux-audit list that keep track of that > stuff), but looking at the opcodes right now my gut feeling is that > most of the opcodes would be considered "security relevant" so > selective auditing might not be that useful in practice. It would > definitely clutter the code and increase the chances that new opcodes > would not be properly audited when they are merged. We don't audit read/write from aio, as mentioned. In the past two decades, I take it that hasn't been a concern? I agree that some opcodes should _definitely_ be audited. Things like opening a file, closing a file, removing/creating a file, mount, etc. But normal read/write, I think that's just utter noise and not useful at all. Auditing on a per-opcode basis is trivial, io_uring already has provisions for flagging opcode requirements and this would just be another one. -- Jens Axboe