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=-4.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 D0AE9C47082 for ; Wed, 26 May 2021 10:19:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B515861442 for ; Wed, 26 May 2021 10:19:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233879AbhEZKUv (ORCPT ); Wed, 26 May 2021 06:20:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60794 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233793AbhEZKUv (ORCPT ); Wed, 26 May 2021 06:20:51 -0400 Received: from mail-wr1-x42e.google.com (mail-wr1-x42e.google.com [IPv6:2a00:1450:4864:20::42e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 97863C061574; Wed, 26 May 2021 03:19:18 -0700 (PDT) Received: by mail-wr1-x42e.google.com with SMTP id p7so491115wru.10; Wed, 26 May 2021 03:19:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=to:cc:references:from:subject:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=z+Ri2n3Ocsu19UbwoKK73grQnRbFQovYzLp7sCDG7XU=; b=HT2qdFrJEOcbSqmn0mj2PZXPRGJPTyWLMUq4Sz5FBCUsKzvBMnojJApDwbnIG2Jcwq CObn/SIeDSWdNbEm2Q0vOyG7B/T/jQtWsobjvyGytUJ0a0GFSOZ8HZPhqXl+MyOhqDn+ 21oHC+3cyl/2rSO3q9WeQ9HVIEUNzSNHhIRrxXmRtcuOY4FA/Po5GYpgu9lpJRSy8MoO PXnRAHw2NlZ5naEUFKX7UhGXyCYpOyi4L1DwxatAMiOg+CYwRHPBVvFmFnq77FOhhPvC /QhsjLiZMF9jgrleP2f/GTD3oELCq0SihHcojHWjksoRBHvqS8WiSHuyvtr5HyizyoUX mi5w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:to:cc:references:from:subject:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=z+Ri2n3Ocsu19UbwoKK73grQnRbFQovYzLp7sCDG7XU=; b=qItsuLbon3SrGakcsPpHIDITwz2D6Vf9P79gd19mr5aADFURjUz5rgaP1I3z372j9i x6G/xiZ0sW6wk8lt1lyD3Egr9+EdOWlh9ZCWGJMOANZHhxMpjwuSuTHeDgzejVZcTVRX jTLJoPO+lIjRMQdmgZ/uP2JdOT1b6C5LZdy3SMatEIGpEgyZNxd5Qzwg/9V+Qw4HVXYk t7+g32mG45PBKshyXzzSu6uQ9Z/2o80hCIsVkrMBMVOiSuAylqYcGTb7knNeBUCGhcQc uieNebLlHZSFFZhmngkFdObb/G2D1E2Pf/cBX/2y99WR2vy1EkWj5sM255zF1JSJOk99 6SMg== X-Gm-Message-State: AOAM530d/rwpWD8SFOiJTu1i/1JjJn0fEGNuxpgjFIm4Y9XL7UCXDrKN T0e/swJHCyokd6C/19bBR30= X-Google-Smtp-Source: ABdhPJywganIcqZjZaYvnZH3uWCkDwi9O5Ktdyk9fsy+ejFwjvibA7TSYKN66vm6LiQxTCnmYRzmCQ== X-Received: by 2002:a5d:5407:: with SMTP id g7mr32338951wrv.207.1622024357214; Wed, 26 May 2021 03:19:17 -0700 (PDT) Received: from [192.168.8.197] ([85.255.235.102]) by smtp.gmail.com with ESMTPSA id u8sm5538665wmq.29.2021.05.26.03.19.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 26 May 2021 03:19:16 -0700 (PDT) To: Paul Moore , Jens Axboe Cc: 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: Pavel Begunkov Subject: Re: [RFC PATCH 2/9] audit,io_uring,io-wq: add some basic audit support to io_uring Message-ID: <0a668302-b170-31ce-1651-ddf45f63d02a@gmail.com> Date: Wed, 26 May 2021 11:19:08 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 5/26/21 3:04 AM, 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); > + } I'd rather agree that it's my cycle-picking. The case I care about is CONFIG_AUDIT=y (because everybody enable it), and io_uring tracing _not_ enabled at runtime. If enabled let them suffer the overhead, it will probably dip down the performance So, for the case I care about it's two of if (unlikely(audit_enabled && current->audit_context)) in the hot path. load-test-jump + current, so it will be around 7x2 instructions. We can throw away audit_enabled as you say systemd already enables it, that will give 4x2 instructions including 2 conditional jumps. That's not great at all. And that's why I brought up the question about need of pre and post hooks and whether can be combined. Would be just 4 instructions and that is ok (ish). > 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. I'm curious, why it's enabled by many distros by default? Are there use cases they use? Tempting to add AUDIT_IOURING=default N, but won't work I guess -- Pavel Begunkov