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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 DF32CC43331 for ; Fri, 27 Mar 2020 18:14:11 +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 A1AEE2071B for ; Fri, 27 Mar 2020 18:14:11 +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="eE3cP1Jc" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A1AEE2071B 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]:45276 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jHtUg-0002jV-QF for qemu-devel@archiver.kernel.org; Fri, 27 Mar 2020 14:14:10 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:40409) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jHtTn-0001W3-VV for qemu-devel@nongnu.org; Fri, 27 Mar 2020 14:13:17 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jHtTl-0000EJ-Rq for qemu-devel@nongnu.org; Fri, 27 Mar 2020 14:13:15 -0400 Received: from us-smtp-delivery-74.mimecast.com ([63.128.21.74]:31138) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1jHtTl-0000CO-LP for qemu-devel@nongnu.org; Fri, 27 Mar 2020 14:13:13 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1585332792; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=XkOmjQYazMSwSs0atc9MFIyLa1D9Ojb+vEtUmSJjVUs=; b=eE3cP1JcvyV6i2vNo2VLcSsM9ln/96yUP5EmuSFqTK3WwhDrOR2xQOGMgAB+ayFfLdVMrg Q71/G+FALq70d00c/8lU9touD3Cl/bh1YMvbvOC59+OE3QIQBzXdcKyzMQSFke2umlskTM 5OJ+0S8sUOq1Plx9GkeGD4iXrsxc99c= 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-18-3TJzslYVPRKIoQRtVJfJbQ-1; Fri, 27 Mar 2020 14:13:07 -0400 X-MC-Unique: 3TJzslYVPRKIoQRtVJfJbQ-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 70AA118A6EC1; Fri, 27 Mar 2020 18:13:06 +0000 (UTC) Received: from [10.3.113.103] (ovpn-113-103.phx2.redhat.com [10.3.113.103]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D9B001001901; Fri, 27 Mar 2020 18:13:04 +0000 (UTC) Subject: Re: [PATCH v3] qcow2: Forbid discard in qcow2 v2 images with backing files To: Alberto Garcia , qemu-devel@nongnu.org References: <20200327164857.31415-1-berto@igalia.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: Date: Fri, 27 Mar 2020 13:13:04 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200327164857.31415-1-berto@igalia.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 63.128.21.74 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: Kevin Wolf , =?UTF-8?Q?Daniel_P_=2e_Berrang=c3=a9?= , qemu-block@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 3/27/20 11:48 AM, Alberto Garcia wrote: > A discard request deallocates the selected clusters so they read back > as zeroes. This is done by clearing the cluster offset field and > setting QCOW_OFLAG_ZERO in the L2 entry. > > This flag is however only supported when qcow_version >= 3. In older > images the cluster is simply deallocated, exposing any possible stale > data from the backing file. > > Since discard is an advisory operation it's safer to simply forbid it > in this scenario. > > Note that we are adding this check to qcow2_co_pdiscard() and not to > qcow2_cluster_discard() or discard_in_l2_slice() because the last > two are also used by qcow2_snapshot_create() to discard the clusters > used by the VM state. In this case there's no risk of exposing stale > data to the guest and we really want that the clusters are always > discarded. > > Signed-off-by: Alberto Garcia > --- > +++ b/tests/qemu-iotests/290 > + > +echo > +echo "### Test 'qemu-io -c discard' on a QCOW2 image without a backing file" > +echo > +for qcow2_compat in 0.10 1.1; do > + echo "# Create an image with compat=$qcow2_compat without a backing file" > + _make_test_img -o "compat=$qcow2_compat" 128k > + > + echo "# Fill all clusters with data and then discard them" > + $QEMU_IO -c 'write -P 0x01 0 128k' "$TEST_IMG" | _filter_qemu_io > + $QEMU_IO -c 'discard 0 128k' "$TEST_IMG" | _filter_qemu_io > + > + echo "# Read the data from the discarded clusters" > + $QEMU_IO -c 'read -P 0x00 0 128k' "$TEST_IMG" | _filter_qemu_io > +done Should this loop also inspect qemu-img map output? > + > +echo > +echo "### Test 'qemu-io -c discard' on a QCOW2 image with a backing file" > +echo > + > +echo "# Create a backing image and fill it with data" > +BACKING_IMG="$TEST_IMG.base" > +TEST_IMG="$BACKING_IMG" _make_test_img 128k > +$QEMU_IO -c 'write -P 0xff 0 128k' "$BACKING_IMG" | _filter_qemu_io > + > +for qcow2_compat in 0.10 1.1; do > + echo "# Create an image with compat=$qcow2_compat and a backing file" > + _make_test_img -o "compat=$qcow2_compat" -b "$BACKING_IMG" > + > + echo "# Fill all clusters with data and then discard them" > + $QEMU_IO -c 'write -P 0x01 0 128k' "$TEST_IMG" | _filter_qemu_io > + $QEMU_IO -c 'discard 0 128k' "$TEST_IMG" | _filter_qemu_io > + > + echo "# Read the data from the discarded clusters" > + if [ "$qcow2_compat" = "1.1" ]; then > + # In qcow2 v3 clusters are zeroed (with QCOW_OFLAG_ZERO) > + $QEMU_IO -c 'read -P 0x00 0 128k' "$TEST_IMG" | _filter_qemu_io > + else > + # In qcow2 v2 if there's a backing image we cannot zero the clusters > + # without exposing the backing file data so discard does nothing > + $QEMU_IO -c 'read -P 0x01 0 128k' "$TEST_IMG" | _filter_qemu_io > + fi > + > + echo "# Output of qemu-img map" > + $QEMU_IMG map "$TEST_IMG" | _filter_testdir > +done But I agree this was the more interesting one, so we at least have decent coverage of the change itself. Reviewed-by: Eric Blake -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org