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=-9.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 5B86CC388F9 for ; Tue, 27 Oct 2020 13:05:54 +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 CC69322202 for ; Tue, 27 Oct 2020 13:05:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Gi1og6oO" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CC69322202 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]:60416 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kXOfg-00068q-Js for qemu-devel@archiver.kernel.org; Tue, 27 Oct 2020 09:05:52 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:43834) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kXOWc-0004tV-HL for qemu-devel@nongnu.org; Tue, 27 Oct 2020 08:56:30 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:45739) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kXOWa-0001r4-JZ for qemu-devel@nongnu.org; Tue, 27 Oct 2020 08:56:30 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1603803387; 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=fFCAvh84kUuCi3uUfZcQzgj6nr81o1ebXnM97gk5LpU=; b=Gi1og6oO5CYp8HNbYmOEyUDMkqNHoxz5GVIDGLNpem8/iR1x26yY4ULOihRqTLbIHOvA8n kOBGaiApvJ3dQJxI/4U9MQ1hyWNAfvf7a1/NO2WSWzB2oeVdtf/OUo1xQGLZWhYkhcxwH9 2YaLnEzuyzRMYT600m60Yfibk4z/BJ4= 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-316-m6h9jj-sMZu9u6ccy7vAZQ-1; Tue, 27 Oct 2020 08:56:23 -0400 X-MC-Unique: m6h9jj-sMZu9u6ccy7vAZQ-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4E651188C130; Tue, 27 Oct 2020 12:56:22 +0000 (UTC) Received: from redhat.com (ovpn-115-179.ams2.redhat.com [10.36.115.179]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8FA555D9E4; Tue, 27 Oct 2020 12:56:16 +0000 (UTC) Date: Tue, 27 Oct 2020 08:56:12 -0400 From: "Michael S. Tsirkin" To: Felipe Franciosi Subject: Re: [PATCH] virtio: skip guest index check on device load Message-ID: <20201027085447-mutt-send-email-mst@kernel.org> References: <20201026151328.77611-1-felipe@nutanix.com> <20201027113049.GH79063@stefanha-x1.localdomain> <20201027082337-mutt-send-email-mst@kernel.org> <12146644-5D22-4CAC-9B4F-F16E84ED56AE@nutanix.com> MIME-Version: 1.0 In-Reply-To: <12146644-5D22-4CAC-9B4F-F16E84ED56AE@nutanix.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=63.128.21.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/27 01:06:07 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: Paolo Bonzini , Jason Wang , "qemu-devel@nongnu.org" , Stefan Hajnoczi , Markus Armbruster Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Oct 27, 2020 at 12:53:29PM +0000, Felipe Franciosi wrote: > > > > On Oct 27, 2020, at 12:25 PM, Michael S. Tsirkin wrote: > > > > On Tue, Oct 27, 2020 at 11:30:49AM +0000, Stefan Hajnoczi wrote: > >> On Mon, Oct 26, 2020 at 03:13:32PM +0000, Felipe Franciosi wrote: > >>> QEMU must be careful when loading device state off migration streams to > >>> prevent a malicious source from exploiting the emulator. Overdoing these > >>> checks has the side effect of allowing a guest to "pin itself" in cloud > >>> environments by messing with state which is entirely in its control. > >>> > >>> Similarly to what f3081539 achieved in usb_device_post_load(), this > >>> commit removes such a check from virtio_load(). Worth noting, the result > >>> of a load without this check is the same as if a guest enables a VQ with > >>> invalid indexes to begin with. That is, the virtual device is set in a > >>> broken state (by the datapath handler) and must be reset. > >>> > >>> Signed-off-by: Felipe Franciosi > >>> --- > >>> hw/virtio/virtio.c | 12 ------------ > >>> 1 file changed, 12 deletions(-) > >>> > >>> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > >>> index 6f8f865aff..0561bdb857 100644 > >>> --- a/hw/virtio/virtio.c > >>> +++ b/hw/virtio/virtio.c > >>> @@ -3136,8 +3136,6 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id) > >>> RCU_READ_LOCK_GUARD(); > >>> for (i = 0; i < num; i++) { > >>> if (vdev->vq[i].vring.desc) { > >>> - uint16_t nheads; > >>> - > >>> /* > >>> * VIRTIO-1 devices migrate desc, used, and avail ring addresses so > >>> * only the region cache needs to be set up. Legacy devices need > >>> @@ -3157,16 +3155,6 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id) > >>> continue; > >>> } > >>> > >>> - nheads = vring_avail_idx(&vdev->vq[i]) - vdev->vq[i].last_avail_idx; > >>> - /* Check it isn't doing strange things with descriptor numbers. */ > >>> - if (nheads > vdev->vq[i].vring.num) { > >>> - error_report("VQ %d size 0x%x Guest index 0x%x " > >>> - "inconsistent with Host index 0x%x: delta 0x%x", > >>> - i, vdev->vq[i].vring.num, > >>> - vring_avail_idx(&vdev->vq[i]), > >>> - vdev->vq[i].last_avail_idx, nheads); > >>> - return -1; > >>> - } > >> > >> Michael, the commit that introduced this check seems to have been for > >> debugging rather than to prevent a QEMU crash, so this removing the > >> check may be safe: > >> > >> commit 258dc7c96bb4b7ca71d5bee811e73933310e168c > >> Author: Michael S. Tsirkin > >> Date: Sun Oct 17 20:23:48 2010 +0200 > >> > >> virtio: sanity-check available index > >> > >> Checking available index upon load instead of > >> only when vm is running makes is easier to > >> debug failures. > > > > Agreed. Given this, let's keep the message around, just with > > LOG_GUEST_ERROR ? > > I thought about it. Happy to send a v2 which keeps the check and logs > without throwing an error. > > Separately, I'm thinking of hooking up QEMU with VRING_ERR so datapath > handlers can notify QEMU that something went broken and NEEDS_RESET > can be flipped on the status register, possibly along a configuration > interrupt. I can see libvhost-user supports that, but are there any > reasons QEMU doesn't do this already? Mostly because guest support isn't there. That in turn isn't easy, lots of synchronization is needed within guests. > > > >> Felipe: Did you audit the code to make sure the invalid avail_idx value > >> and the fields it is propagated to (e.g. shadow_avail_idx) are always > >> used in a safe way? > > > > I did it briefly. I also wrote a mock userspace driver that creates > this condition in a very controlled way (so I can step half-way > through setting up VQs and trigger a migration, for example). But you > know how manual tests are... I may have missed something. > Your expert eyes are most welcome. :) > > F.