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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS autolearn=ham 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 672FAC433B4 for ; Wed, 12 May 2021 11:32:09 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A7E34613CD for ; Wed, 12 May 2021 11:32:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A7E34613CD Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=bugs.launchpad.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:59818 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lgn5x-0003x5-Jc for qemu-devel@archiver.kernel.org; Wed, 12 May 2021 07:32:05 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:46680) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lgn4j-0002Wu-7z for qemu-devel@nongnu.org; Wed, 12 May 2021 07:30:49 -0400 Received: from indium.canonical.com ([91.189.90.7]:36940) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1lgn4h-0002gA-Bp for qemu-devel@nongnu.org; Wed, 12 May 2021 07:30:49 -0400 Received: from loganberry.canonical.com ([91.189.90.37]) by indium.canonical.com with esmtp (Exim 4.93 #5 (Debian)) id 1lgn4f-0004zb-P2 for ; Wed, 12 May 2021 11:30:45 +0000 Received: from loganberry.canonical.com (localhost [127.0.0.1]) by loganberry.canonical.com (Postfix) with ESMTP id B22D22E8187 for ; Wed, 12 May 2021 11:30:45 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Date: Wed, 12 May 2021 11:22:52 -0000 From: Thomas Huth <1911351@bugs.launchpad.net> To: qemu-devel@nongnu.org X-Launchpad-Notification-Type: bug X-Launchpad-Bug: product=qemu; status=Incomplete; importance=Undecided; assignee=None; X-Launchpad-Bug-Tags: i386 tcg X-Launchpad-Bug-Information-Type: Public X-Launchpad-Bug-Private: no X-Launchpad-Bug-Security-Vulnerability: no X-Launchpad-Bug-Commenters: charco pmaydell th-huth venkatesh-srinivas X-Launchpad-Bug-Reporter: Marco (charco) X-Launchpad-Bug-Modifier: Thomas Huth (th-huth) References: <161049230444.13717.10732991676985431455.malonedeb@gac.canonical.com> Message-Id: <162081857295.23460.13861539276458656141.malone@soybean.canonical.com> Subject: [Bug 1911351] Re: x86-64 MTTCG Does not update page table entries atomically X-Launchpad-Message-Rationale: Subscriber (QEMU) @qemu-devel-ml X-Launchpad-Message-For: qemu-devel-ml Precedence: bulk X-Generated-By: Launchpad (canonical.com); Revision="37ef8bff8cdf61b994f9b61bc9239663cb29cec9"; Instance="production" X-Launchpad-Hash: 1caef716d07acd422e04ca15e9103250977d969e Received-SPF: none client-ip=91.189.90.7; envelope-from=bounces@canonical.com; helo=indium.canonical.com X-Spam_score_int: -65 X-Spam_score: -6.6 X-Spam_bar: ------ X-Spam_report: (-6.6 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.25, RCVD_IN_DNSWL_HI=-5, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Bug 1911351 <1911351@bugs.launchpad.net> Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" The QEMU project is currently moving its bug tracking to another system. For this we need to know which bugs are still valid and which could be closed already. Thus we are setting the bug state to "Incomplete" now. If the bug has already been fixed in the latest upstream version of QEMU, then please close this ticket as "Fix released". If it is not fixed yet and you think that this bug report here is still valid, then you have two options: 1) If you already have an account on gitlab.com, please open a new ticket for this problem in our new tracker here: https://gitlab.com/qemu-project/qemu/-/issues and then close this ticket here on Launchpad (or let it expire auto- matically after 60 days). Please mention the URL of this bug ticket on Launchpad in the new ticket on GitLab. 2) If you don't have an account on gitlab.com and don't intend to get one, but still would like to keep this ticket opened, then please switch the state back to "New" or "Confirmed" within the next 60 days (other- wise it will get closed as "Expired"). We will then eventually migrate the ticket automatically to the new system (but you won't be the reporter of the bug in the new system and thus you won't get notified on changes anymore). Thank you and sorry for the inconvenience. ** Changed in: qemu Status: Confirmed =3D> Incomplete -- = You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1911351 Title: x86-64 MTTCG Does not update page table entries atomically Status in QEMU: Incomplete Bug description: It seems like the qemu tcg code for x86-64 doesn't write the access and dirty bits of the page table entries atomically. Instead, they first read the entry, see if they need to set the page table entry, and then write back the updated page table entry. So if you have two threads running at the same time, one accessing the virtual address over and over again, and the other modifying the page table entry, it is possible that after the second thread modifies the page table entry, qemu overwrites the value with the old page table entry value, with the access/dirty flags set. Here's a unit test that reproduces this behavior: https://github.com/mvanotti/kvm-unit- tests/commit/09f9722807271226a714b04f25174776454b19cd You can run it with: ``` /usr/bin/qemu-system-x86_64 --no-reboot -nodefaults \ -device pc-testdev -device isa-debug-exit,iobase=3D0xf4,iosize=3D0x4 \ -vnc none -serial stdio -device pci-testdev \ -smp 4 -machine q35 --accel tcg,thread=3Dmulti \ -kernel x86/mmu-race.flat # -initrd /tmp/tmp.avvPpezMFf ``` Expected output (failure): ``` kvm-unit-tests$ make && /usr/bin/qemu-system-x86_64 --no-reboot -nodefaul= ts -device pc-testdev -device isa-debug-exit,iobase=3D0xf4,iosize=3D0x4 -vn= c none -serial stdio -device pci-testdev -smp 4 -machine q35 --accel tcg,th= read=3Dmulti -kernel x86/mmu-race.flat # -initrd /tmp/tmp.avvPpezMFf enabling apic enabling apic enabling apic enabling apic paging enabled cr0 =3D 80010011 cr3 =3D 627000 cr4 =3D 20 found 4 cpus PASS: Need more than 1 CPU Detected overwritten PTE: =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0want: 0x000000000062e007 =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0got: 0x000000000062d027 FAIL: PTE not overwritten PASS: All Reads were zero SUMMARY: 3 tests, 1 unexpected failures ``` This bug allows user-to-root privilege escalation inside the guest VM: if the user is able overwrite an entry that belongs to a second-to- last level page table, and is able to allocate the referenced page, then the user would be in control of a last-level page table, being able to map any memory they want. This is not uncommon in situations where memory is being decomitted. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1911351/+subscriptions