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=-7.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 CC89CC47088 for ; Wed, 26 May 2021 15:49:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AB5D5613DE for ; Wed, 26 May 2021 15:49:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234547AbhEZPv3 (ORCPT ); Wed, 26 May 2021 11:51:29 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:20739 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235221AbhEZPvP (ORCPT ); Wed, 26 May 2021 11:51:15 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1622044168; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=r1Ej9c3HqF4N34dLokWBDDDLrsUjOS1R2qnUxM+2GaA=; b=VMhFHGBF1oLVpsFcJ1cAJMwFwl663bVg9OK1ZO2bg1Fzt1SEiQ1CUi5Nc9TkbnXK6iZJgL JkS9/c30ZGQk95l4ue62YInZhrcE4F0LMiK7is51cWRe7nQkqr/+rtCO7vOPLNE2m5f7vP g1m9TJOd350wJ5MmT4TtlhktEXh9bqE= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-270-8ehnYgxmNmaY3t-x9HlAHw-1; Wed, 26 May 2021 11:49:18 -0400 X-MC-Unique: 8ehnYgxmNmaY3t-x9HlAHw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 15355188E3C1; Wed, 26 May 2021 15:49:17 +0000 (UTC) Received: from madcap2.tricolour.ca (unknown [10.3.128.13]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CE0AC90BE; Wed, 26 May 2021 15:49:07 +0000 (UTC) Date: Wed, 26 May 2021 11:49:05 -0400 From: Richard Guy Briggs To: Stefan Metzmacher Cc: Paul Moore , Pavel Begunkov , Jens Axboe , selinux@vger.kernel.org, linux-security-module@vger.kernel.org, linux-audit@redhat.com, Kumar Kartikeya Dwivedi , linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org, Alexander Viro Subject: Re: [RFC PATCH 2/9] audit,io_uring,io-wq: add some basic audit support to io_uring Message-ID: <20210526154905.GJ447005@madcap2.tricolour.ca> References: <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> <18823c99-7d65-0e6f-d508-a487f1b4b9e7@samba.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <18823c99-7d65-0e6f-d508-a487f1b4b9e7@samba.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 2021-05-26 17:17, Stefan Metzmacher wrote: > > 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. The audit context needs to be set up for each event. This happens in audit_syslog_entry and audit_syslog_exit. > 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(). These are extra hooks to grab operation-specific (syscall) parameters. > So why is there anything special needed for io_uring (now that the native worker threads are used)? Because syscall has been bypassed by a memory-mapped work queue. > 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... This is by design to speed it up. This is what Paul's iouring entry and exit hooks do. > 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 - RGB -- Richard Guy Briggs Sr. S/W Engineer, Kernel Security, Base Operating Systems Remote, Ottawa, Red Hat Canada IRC: rgb, SunRaycer Voice: +1.647.777.2635, Internal: (81) 32635