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=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 B8505C4708A for ; Wed, 26 May 2021 15:17:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AC7E4613D3 for ; Wed, 26 May 2021 15:17:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233413AbhEZPTW (ORCPT ); Wed, 26 May 2021 11:19:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44484 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233431AbhEZPTV (ORCPT ); Wed, 26 May 2021 11:19:21 -0400 Received: from hr2.samba.org (hr2.samba.org [IPv6:2a01:4f8:192:486::2:0]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C2416C061574; Wed, 26 May 2021 08:17:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=samba.org; s=42; h=Date:Message-ID:From:Cc:To; bh=co12ff4tTNF+KNx1GGZqG+qS13NxRQukgTFUVlXw18g=; b=X3ttPkyMClgHXbWUbhqY0orK7W +6CUwKmekqBcBBt5U7jQbifCtm+WLLTrIPj9aUbT/zsDFP/Beynzw0xsp8TCNDBpdtHxmZBqV0ir5 S/kGWSFAr+x/4174GRohYjk+RznlTyb1Gj8eN7bqYt6yANCDpGoLCWi1SJSEa9qQd1byheeC/sEoK lq88911kkgSJS7hBg0OdN/nGwOs+60RqZVu6SNctSJLKKqE/gkYlJ8BVVuljAZCbZD+CUzwLEifH/ LXohvn2xUHot/oO1kA/fK1nmEFZ43dKaXiIU8o0LbEW7uTcIe/z+6i9Y+xXRZzf9DqUITyo7hkFcW JJL+HTjDOhHzNb0HSP3mVT/8EGnM+scPgnaIEluhFqXwejnLMB8dAzqwTX8YQ4va+ihQedmFKhzo1 iNfRJAc6IaaRIxta9zxy4amEMgROIBYD2IsWkFqnv+iaVc2RHXm9TxEYp2F6u3IbZPRT+NPOBH3pC FCG8fDjgLqB19X7KT8rwoI9a; Received: from [127.0.0.2] (localhost [127.0.0.1]) by hr2.samba.org with esmtpsa (TLS1.3:ECDHE_RSA_CHACHA20_POLY1305:256) (Exim) id 1llvI3-0000gU-9J; Wed, 26 May 2021 15:17:47 +0000 To: Paul Moore , 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 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> <0a668302-b170-31ce-1651-ddf45f63d02a@gmail.com> From: Stefan Metzmacher Subject: Re: [RFC PATCH 2/9] audit,io_uring,io-wq: add some basic audit support to io_uring Message-ID: <18823c99-7d65-0e6f-d508-a487f1b4b9e7@samba.org> Date: Wed, 26 May 2021 17:17:46 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 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 Am 26.05.21 um 16:38 schrieb Paul Moore: > On Wed, May 26, 2021 at 6:19 AM Pavel Begunkov wrote: >> 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. > > We've basically got it down to the equivalent of two > "current->audit_context != NULL" checks in the case where audit is > built into the kernel but disabled at runtime, e.g. CONFIG_AUDIT=y and > "task,never". I'm at a loss for how we can lower the overhead any > further, but I'm open to suggestions. > >> 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). > > As discussed previously in this thread that isn't really an option > from an audit perspective. > >>> 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? > > We've already talked about certain users and environments where audit > is an important requirement, e.g. public sector, health care, > financial institutions, etc.; without audit Linux wouldn't be an > option for these users, at least not without heavy modification, > out-of-tree/ISV patches, etc. I currently don't have any direct ties > to any distros, "Enterprise" or otherwise, but in the past it has been > my experience that distros much prefer to have a single kernel build > to address the needs of all their users. In the few cases I have seen > where a second kernel build is supported it is usually for hardware > enablement. I'm sure there are other cases too, I just haven't seen > them personally; the big distros definitely seem to have a strong > desire to limit the number of supported kernel configs/builds. > >> Tempting to add AUDIT_IOURING=default N, but won't work I guess > > One of the nice things about audit is that it can give you a history > of what a user did on a system, which is very important for a number > of use cases. If we selectively disable audit for certain subsystems > we create a blind spot in the audit log, and in the case of io_uring > this can be a very serious blind spot. I fear that if we can't come > to some agreement here we will need to make io_uring and audit > mutually exclusive at build time which would be awful; forcing many > distros to either make a hard choice or carry out-of-tree patches. I'm wondering why it's not enough to have the native auditing just to happen. E.g. all (I have checked RECVMSG,SENDMSG,SEND and CONNECT) socket related io_uring opcodes already go via security_socket_{recvmsg,sendmsg,connect}() IORING_OP_OPENAT* goes via do_filp_open() which is in common with the open[at[2]]() syscalls and should also trigger audit_inode() and security_file_open(). So why is there anything special needed for io_uring (now that the native worker threads are used)? Is there really any io_uring opcode that bypasses the security checks the corresponding native syscall would do? If so, I think that should just be fixed... Additional LSM based restrictions could be hooked into the io_check_restriction() path and setup at io_uring_setup() or early io_uring_register() time. What do you think? metze