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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 CDC67C433DF for ; Tue, 16 Jun 2020 09:13:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A1BC120679 for ; Tue, 16 Jun 2020 09:13:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="XyNypN9l" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728113AbgFPJNB (ORCPT ); Tue, 16 Jun 2020 05:13:01 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:38522 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725896AbgFPJM6 (ORCPT ); Tue, 16 Jun 2020 05:12:58 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1592298776; 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=KpFMwGKnCWLslGz1ShbrW/qNgT9EYfVeEgEKH929dV8=; b=XyNypN9lLlgnPFGZfwmo0Fl6xJHxq+iBo+VsniagHJgm0FwB6Ri0pTP7MRmu3X1MAP3bb6 XsFI21yZpiM9+YFrC/PduMI/UQoSJCHb72qZPxKshgdWAUJhd5o303BzXWFHe0KtmF0uC8 J5XZr7/ra74rTfJxEARplOuiMZfhLRQ= Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-48-SUgPsaCDPIiCf3CXpMpYfA-1; Tue, 16 Jun 2020 05:12:53 -0400 X-MC-Unique: SUgPsaCDPIiCf3CXpMpYfA-1 Received: by mail-wr1-f72.google.com with SMTP id l18so8102350wrm.0 for ; Tue, 16 Jun 2020 02:12:53 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=KpFMwGKnCWLslGz1ShbrW/qNgT9EYfVeEgEKH929dV8=; b=gOQ+2pDvWZm5cM/RPRHESg/91y7xkTQsInLCuuwmin/5dE9/jSOjQL/90k55hQXZPy VU8AlzUiHCWnqsRZ6DTJkZzab/+U78tm7iSt/0J22lLR2W+Vy9GyWYhdYFsUkXzBooxk ukhpCJT0MA9QbQf5arTcy/Bx9Oadh0dpmqn25u4LDRVn8IgqaChV7SGadcHr+e325vXp CnCoA7E6X16bNpHGwDqN2CvPny0bt+5aBmdgmL8Sj+s7a7uvbg1oHXOpdt3Tkbity4wF IxLKWDv7hG0lDjwCVEWQ9/16iMS6OxST27e6LjSeb1DuKTeYVOnCi22TtYTprhVIWBnd Wezw== X-Gm-Message-State: AOAM531SzT/DQfZQJdp6QfYuwD+xgmPVvRYHxITpQYah8KelyQZRXYM4 1eN5ACVcgDqYWd/i9Bq4Pt9zES7JCxl/+jGqr4yyQaDtPgezWuDAVQ00PTz4Lk6/r3N7RkXOSax 6Ew7oXiBVZYeg6IyMG58ZyzJT X-Received: by 2002:adf:ff83:: with SMTP id j3mr1991783wrr.264.1592298772685; Tue, 16 Jun 2020 02:12:52 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwvcIpIFWszxHkde+5PP2e7SeEMAmFeepnBsxqv+e10s0vJo2qksi76vif4CocolLtCn1yXTA== X-Received: by 2002:adf:ff83:: with SMTP id j3mr1991750wrr.264.1592298772376; Tue, 16 Jun 2020 02:12:52 -0700 (PDT) Received: from steredhat ([5.180.207.22]) by smtp.gmail.com with ESMTPSA id u7sm28820594wrm.23.2020.06.16.02.12.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 16 Jun 2020 02:12:51 -0700 (PDT) Date: Tue, 16 Jun 2020 11:12:47 +0200 From: Stefano Garzarella To: Jens Axboe , Jann Horn Cc: Kees Cook , Christian Brauner , Sargun Dhillon , Aleksa Sarai , Stefan Hajnoczi , Jeff Moyer , io-uring , kernel list , Kernel Hardening Subject: Re: [RFC] io_uring: add restrictions to support untrusted applications and guests Message-ID: <20200616091247.hdmxcrnlrrxih7my@steredhat> References: <20200609142406.upuwpfmgqjeji4lc@steredhat> <20200615133310.qwdmnctrir5zgube@steredhat> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 15, 2020 at 11:00:25AM -0600, Jens Axboe wrote: > On 6/15/20 7:33 AM, Stefano Garzarella wrote: > > On Mon, Jun 15, 2020 at 11:04:06AM +0200, Jann Horn wrote: > >> +Kees, Christian, Sargun, Aleksa, kernel-hardening for their opinions > >> on seccomp-related aspects > >> > >> On Tue, Jun 9, 2020 at 4:24 PM Stefano Garzarella wrote: > >>> Hi Jens, > >>> Stefan and I have a proposal to share with io_uring community. > >>> Before implementing it we would like to discuss it to receive feedbacks and > >>> to see if it could be accepted: > >>> > >>> Adding restrictions to io_uring > >>> ===================================== > >>> The io_uring API provides submission and completion queues for performing > >>> asynchronous I/O operations. The queues are located in memory that is > >>> accessible to both the host userspace application and the kernel, making it > >>> possible to monitor for activity through polling instead of system calls. This > >>> design offers good performance and this makes exposing io_uring to guests an > >>> attractive idea for improving I/O performance in virtualization. > >> [...] > >>> Restrictions > >>> ------------ > >>> This document proposes io_uring API changes that safely allow untrusted > >>> applications or guests to use io_uring. io_uring's existing security model is > >>> that of kernel system call handler code. It is designed to reject invalid > >>> inputs from host userspace applications. Supporting guests as io_uring API > >>> clients adds a new trust domain with access to even fewer resources than host > >>> userspace applications. > >>> > >>> Guests do not have direct access to host userspace application file descriptors > >>> or memory. The host userspace application, a Virtual Machine Monitor (VMM) such > >>> as QEMU, grants access to a subset of its file descriptors and memory. The > >>> allowed file descriptors are typically the disk image files belonging to the > >>> guest. The memory is typically the virtual machine's RAM that the VMM has > >>> allocated on behalf of the guest. > >>> > >>> The following extensions to the io_uring API allow the host application to > >>> grant access to some of its file descriptors. > >>> > >>> These extensions are designed to be applicable to other use cases besides > >>> untrusted guests and are not virtualization-specific. For example, the > >>> restrictions can be used to allow only a subset of sqe operations available to > >>> an application similar to seccomp syscall whitelisting. > >>> > >>> An address translation and memory restriction mechanism would also be > >>> necessary, but we can discuss this later. > >>> > >>> The IOURING_REGISTER_RESTRICTIONS opcode > >>> ---------------------------------------- > >>> The new io_uring_register(2) IOURING_REGISTER_RESTRICTIONS opcode permanently > >>> installs a feature whitelist on an io_ring_ctx. The io_ring_ctx can then be > >>> passed to untrusted code with the knowledge that only operations present in the > >>> whitelist can be executed. > >> > >> This approach of first creating a normal io_uring instance and then > >> installing restrictions separately in a second syscall means that it > >> won't be possible to use seccomp to restrict newly created io_uring > >> instances; code that should be subject to seccomp restrictions and > >> uring restrictions would only be able to use preexisting io_uring > >> instances that have already been configured by trusted code. > >> > >> So I think that from the seccomp perspective, it might be preferable > >> to set up these restrictions in the io_uring_setup() syscall. It might > >> also be a bit nicer from a code cleanliness perspective, since you > >> won't have to worry about concurrently changing restrictions. > >> > > > > Thank you for these details! > > > > It seems feasible to include the restrictions during io_uring_setup(). > > > > The only doubt concerns the possibility of allowing the trusted code to > > do some operations, before passing queues to the untrusted code, for > > example registering file descriptors, buffers, eventfds, etc. > > > > To avoid this, I should include these operations in io_uring_setup(), > > adding some code that I wanted to avoid by reusing io_uring_register(). > > > > If I add restrictions in io_uring_setup() and then add an operation to > > go into safe mode (e.g. a flag in io_uring_enter()), we would have the same > > problem, right? > > > > Just to be clear, I mean something like this: > > > > /* params will include restrictions */ > > fd = io_uring_setup(entries, params); > > > > /* trusted code */ > > io_uring_register_files(fd, ...); > > io_uring_register_buffers(fd, ...); > > io_uring_register_eventfd(fd, ...); > > > > /* enable safe mode */ > > io_uring_enter(fd, ..., IORING_ENTER_ENABLE_RESTRICTIONS); > > > > > > Anyway, including a list of things to register in the 'params', passed > > to io_uring_setup(), should be feasible, if Jens agree :-) > > I wonder how best to deal with this, in terms of ring visibility vs > registering restrictions. We could potentially start the ring in a > disabled mode, if asked to. It'd still be visible in terms of having > the fd installed, but it'd just error requests. That'd leave you with > time to do the various setup routines needed before then flagging it > as enabled. My only worry on that would be adding overhead for doing > that. It'd be cheap enough to check for IORING_SETUP_DISABLED in > ctx->flags in io_uring_enter(), and return -EBADFD or something if > that's the case. That doesn't cover the SQPOLL case though, but maybe we > just don't start the sq thread if IORING_SETUP_DISABLED is set. It seems to me a very good approach and easy to implement. In this way we can reuse io_uring_register() without having to modify too much io_uring_setup(). > > We'd need a way to clear IORING_SETUP_DISABLED through > io_uring_register(). When clearing, that could then start the sq thread > as well, when SQPOLL is set. Could we do it using io_uring_enter() since we have a flag field or do you think it's semantically incorrect? @Jann, do you think this could work with seccomp? Thanks, Stefano