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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 58F5DC47082 for ; Wed, 26 May 2021 19:10:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 365F5613B5 for ; Wed, 26 May 2021 19:10:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232985AbhEZTLz (ORCPT ); Wed, 26 May 2021 15:11:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41304 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233383AbhEZTLy (ORCPT ); Wed, 26 May 2021 15:11:54 -0400 Received: from mail-ed1-x52d.google.com (mail-ed1-x52d.google.com [IPv6:2a00:1450:4864:20::52d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 11FEFC06175F for ; Wed, 26 May 2021 12:10:20 -0700 (PDT) Received: by mail-ed1-x52d.google.com with SMTP id s6so2793507edu.10 for ; Wed, 26 May 2021 12:10:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=paul-moore-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=+eZ8wRfiyLlH3ilFo/PCrE+00rbBTnqHgmAoOKQiukI=; b=wfxDILfQbXUke1pK/1yMJqcB/GDZ4hVgpuKlzQDJe+tosiJqp9OqdD/0Y7qE1v5K0+ Q+kuGokdWTSM5nC73vz9ZOHQNSY7svMAd2HL6L9uJ+GLRMWEtF8rnIRcideaqkuxIN4I OyWBPM0H0MPXuSEDXejoJG4sOmVHqklD2PdY4Xokzc0uDEV9rWEjtY90gW6a68p77HR6 TMxQA9w0csQ/u8jSOZGW/ALtIc06FpF0wwSdKjTvlAM4cuRal0EK0sl3Yeomc5x68Nox wfcWx/ZydFHHJ3jNeAasY86qn5XX2orTRwFonF8DkW5U5Wa3iMgxpZSu0NOhG08fgx8k 9R/g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=+eZ8wRfiyLlH3ilFo/PCrE+00rbBTnqHgmAoOKQiukI=; b=pGkCqlFZtH+ElWImvvgnsR2XVYF2obSj88gd5dgnz7wHonbXC174IHE4Qihmpyatv+ ESRnPbDJgka+GnSvz3aZJ8MXTCFJNbkytfdgfYTsjgtWDfev6TGZgXhYGDEvsd1Ki+tJ BaT74OZTp0BvQ2xsYj7r1kuRMxdHR3uKcU5VuRl/+A/9BH2+Oprn9t0HHKDOtY451nlU Y1jSxeo2VTNii2lwew6LTpBQT8pytJxvzV7nryEKybOVV1Urz8QbR/u8jhz2n+BGfZEq 2yP1dKgqasKilpNO27bqbt+0UHsJRwjJU5tziDRHBSGsiAwm0/7kguDjKSo8fW2v1o1x OUAg== X-Gm-Message-State: AOAM530DBCTQ3ExVzqxS7gQZMRzFAU1oQzWE85clQB3PecVbdTZ45uJG +V+lJDchpMqrIIDSOki/3gB6kplYfOstVfkiMpx4 X-Google-Smtp-Source: ABdhPJxcSpVv9HmHaO8wWnezfmJ5wJz+SLYtjyQCEVJTQuLOTM1DL3x23uy6+LsMdvC7TlQRfBqtJFiubAUvvxwVwvk= X-Received: by 2002:a05:6402:430b:: with SMTP id m11mr21422243edc.31.1622056218965; Wed, 26 May 2021 12:10:18 -0700 (PDT) MIME-Version: 1.0 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> <9e69e4b6-2b87-a688-d604-c7f70be894f5@kernel.dk> <3bef7c8a-ee70-d91d-74db-367ad0137d00@kernel.dk> <45688a09-7489-f524-e5ac-e614437f08ea@gmail.com> In-Reply-To: <45688a09-7489-f524-e5ac-e614437f08ea@gmail.com> From: Paul Moore Date: Wed, 26 May 2021 15:10:07 -0400 Message-ID: Subject: Re: [RFC PATCH 2/9] audit,io_uring,io-wq: add some basic audit support to io_uring To: Pavel Begunkov Cc: Jens Axboe , 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 Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: On Wed, May 26, 2021 at 2:57 PM Pavel Begunkov wrote: > On 5/26/21 7:44 PM, Paul Moore wrote: > > On Wed, May 26, 2021 at 2:01 PM Jens Axboe wrote: > >> On 5/26/21 11:54 AM, Jens Axboe wrote: > >>> On 5/26/21 11:31 AM, Jens Axboe wrote: > >>>> On 5/26/21 11:15 AM, Jens Axboe wrote: > >>>>> 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! > >>>> > >>>> io_uring also supports a NOP command, which basically just measures > >>>> reqs/sec through the interface. Ran that as well: > >>>> > >>>> Kernel SQPOLL IOPS Perf diff > >>>> --------------------------------------------------------- > >>>> 5.13 0 31.05M 0.0% > >>>> 5.13 + audit 0 25.31M -18.5% > >>>> > >>>> and profile for the latter includes: > >>>> > >>>> + 5.19% io_uring [kernel.vmlinux] [k] __audit_uring_entry > >>>> + 4.31% io_uring [kernel.vmlinux] [k] __audit_uring_exit > >>>> 0.26% io_uring [kernel.vmlinux] [k] __audit_syscall_entry > >>>> 0.08% io_uring [kernel.vmlinux] [k] __audit_syscall_exit > >>> > >>> As Pavel correctly pointed it, looks like auditing is enabled. And > >>> indeed it was! Hence the above numbers is without having turned off > >>> auditing. Running the NOPs after having turned off audit, we get 30.6M > >>> IOPS, which is down about 1.5% from the baseline. The results for the > >>> polled random read test above did _not_ change from this, they are still > >>> down the same amount. > >>> > >>> Note, and I should have included this in the first email, this is not > >>> any kind of argument for or against audit logging. It's purely meant to > >>> be a set of numbers that show how the current series impacts > >>> performance. > >> > >> And finally, just checking if we make it optional per opcode if we see > >> any real impact, and the answer is no. Using the below patch which > >> effectively bypasses audit calls unless the opcode has flagged the need > >> to do so, I cannot measure any difference in perf (as expected). > >> > >> To turn this into something useful, my suggestion as a viable path > >> forward would be: > >> > >> 1) Use something like the below patch and flag request types that we > >> want to do audit logging for. > >> > >> 2) As Pavel suggested, eliminate the need for having both and entry/exit > >> hook, turning it into just one. That effectively cuts the number of > >> checks and calls in half. > > > > I suspect the updated working-io_uring branch with HEAD at > > 1f25193a3f54 (updated a short time ago, see my last email in this > > thread) will improve performance. Also, as has been mention several > > See the email you replied to, ~1.5% was basically an overhead of > two `if (io_op_defs[req->opcode].audit)` in case of nops, where at > least once req->opcode is cached. But to be completely fair, misses > unlikely Maybe. I remain skeptical that "io_op_defs[req->opcode].audit" has the same cost as "unlikely(audit_context())". -- paul moore www.paul-moore.com