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 C6338C388F9 for ; Tue, 27 Oct 2020 13:38:47 +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 43CBC218AC for ; Tue, 27 Oct 2020 13:38:47 +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="KRI+OBj1" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 43CBC218AC 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]:55946 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kXPBV-0007GO-TT for qemu-devel@archiver.kernel.org; Tue, 27 Oct 2020 09:38:45 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:47400) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kXOes-0005PH-Tv for qemu-devel@nongnu.org; Tue, 27 Oct 2020 09:05:02 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:43032) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kXOeq-0003Bk-M4 for qemu-devel@nongnu.org; Tue, 27 Oct 2020 09:05:02 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1603803898; 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=KhEc9GF+Agx8r2cHEEnEbHXE40/IYJVZQzuq7Lj5ZKI=; b=KRI+OBj1lgrfzfU3oBhvbAEKYvHB3o/KCse9g8nOCJpl4pvGWXsndotcJAvpuvF4nlZCon h68H7AM91pdJUfSoU+1cOX3uP1DV11b6kaHeDi6qzjvVLqeH+T+I+38VyURX+CObHph9Rg ZhNxdxPVvQFaCGlLnocDoWBU2iQtNuI= 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-266-JEHGf9qbN8iXCRhp0ISg5w-1; Tue, 27 Oct 2020 09:04:57 -0400 X-MC-Unique: JEHGf9qbN8iXCRhp0ISg5w-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id DF24159; Tue, 27 Oct 2020 13:04:55 +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 0723810013C0; Tue, 27 Oct 2020 13:04:49 +0000 (UTC) Date: Tue, 27 Oct 2020 09:04:46 -0400 From: "Michael S. Tsirkin" To: Felipe Franciosi Subject: Re: [PATCH] virtio: skip guest index check on device load Message-ID: <20201027090420-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> <20201027085447-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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 01:02:59PM +0000, Felipe Franciosi wrote: > > > > On Oct 27, 2020, at 12:56 PM, Michael S. Tsirkin wrote: > > > > 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. > > Do you mean guest support to reset when seeing that bit in status > following the configuration interrupt? > > It should be safe, though. I can have a stab to see if it breaks > Windows/Linux at least, and share an RFC if I get anywhere. > > Unless you think it's a waste of time. Ideally guests shouldn't find > themselves in this situation to begin with, and if they did, resetting > would arguably just lead them into corruption again (for example). But > it does provide a mechanism for QEMU to find out that the vhost > backend stopped. That would help in the context of this patch. > > F. It's not a waste of time, it's just a lot of work 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. > >