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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 9CCA3C31E40 for ; Mon, 12 Aug 2019 15:49:36 +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 6C69D20679 for ; Mon, 12 Aug 2019 15:49:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6C69D20679 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:46728 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hxCZj-00031T-PP for qemu-devel@archiver.kernel.org; Mon, 12 Aug 2019 11:49:35 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:47849) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hxCYh-0002A7-4N for qemu-devel@nongnu.org; Mon, 12 Aug 2019 11:48:32 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hxCYg-0003nJ-3O for qemu-devel@nongnu.org; Mon, 12 Aug 2019 11:48:31 -0400 Received: from mx1.redhat.com ([209.132.183.28]:4267) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hxCYf-0003mX-UL for qemu-devel@nongnu.org; Mon, 12 Aug 2019 11:48:30 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id ECBF9309DF03; Mon, 12 Aug 2019 15:48:28 +0000 (UTC) Received: from x1.home (ovpn-116-99.phx2.redhat.com [10.3.116.99]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4F33A802EC; Mon, 12 Aug 2019 15:48:15 +0000 (UTC) Date: Mon, 12 Aug 2019 09:48:14 -0600 From: Alex Williamson To: Peter Maydell Message-ID: <20190812094814.24ad5c80@x1.home> In-Reply-To: References: <20190812065221.20907-1-kraxel@redhat.com> <20190812093510.1b85cac8@x1.home> Organization: Red Hat MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Mon, 12 Aug 2019 15:48:29 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH 0/1] display/bochs: fix pcie support (qemu security issue) X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Michael S. Tsirkin" , QEMU Developers , Prasad J Pandit , Gerd Hoffmann , Paolo Bonzini , Philippe =?UTF-8?B?TWF0aGlldS1EYXVkw6k=?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, 12 Aug 2019 16:38:05 +0100 Peter Maydell wrote: > On Mon, 12 Aug 2019 at 16:35, Alex Williamson > wrote: > > Quoting new commit log: > > > > This makes sure the pci config space allocation is big enough, > > so accessing the PCIe extended config space doesn't overflow > > the pci config space buffer. > > > > PCI(e) config space is guest writable. Writes are limited > > bywrite mask (which probably is also filled with random stuff), > > so the guest can only flip enabled bits. But I suspect it > > still might be exploitable, so rather serious because it might > > be a host escape for the guest. On the other hand the device > > is probably not yet in widespread use. > > > > Mitigation: use "-device bochs-display" as conventional pci > > device only. > > > > Is it clear to others that this mitigation remark seems to be > > referencing an alternative configuration constraint to avoid the issue > > rather than what's actually implemented in this patch? IOW, if we > > never place the bochs-display device into a PCIe hierarchy, then > > extended config space is never accessible to the guest anyway, and > > there is no issue. I think this was meant to be an alternative to the > > patch but the enforcement of that would happen above QEMU, probably why > > it was mentioned in the cover letter rather than the original commit > > log. Thanks, > > Yeah, that's unclear in retrospect. How about: > > # (For a QEMU version without this commit, a mitigation for the > # bug is available: use "-device bochs-display" as a conventional pci > # device only.) Yes, better. Thanks, Alex