From nobody Sat Feb 7 10:50:30 2026 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=fail; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com ARC-Seal: i=1; a=rsa-sha256; t=1613995702; cv=none; d=zohomail.com; s=zohoarc; b=oCOLgwVQD/m1kwjQp1g05zXye7oA0svwt09QW+q+QCQoUe9hyiQrwVxE33YX1O2mRkLIXUY7cD5b5dXMfJRu8v4rpIMg5g5C2RDb9QG5bA6FRjy6wZHtKpnenbvXw1TYi7uXOCw2z4t9Qk9u+UxuZoN2rx/IxzxV0rFEFNA6yvU= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1613995702; h=Content-Type:Content-Transfer-Encoding:Cc:Date:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:References:Sender:Subject:To; bh=/dPgg0Kyv23qQF1EHHOV47SNa3sxL4Q1rt18HZe6BYI=; b=gjSZN0rl3JnFUGeumuez6670Lv+YBKuev6T9b6GWv7aot1DYUaAr2ehhW0RvBltc6lcIwhOkXFBv5Zkk+YUakC+paDIIpuXj3fQwNIYREEfKI74DtG3HV9z26BzZYAaIVwk/ZdwgfFYujUZKVQFVGesGsYXdN/7rjkt+lnsIaZs= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=fail; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail header.from= (p=none dis=none) header.from= Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1613995702131842.5478018913176; Mon, 22 Feb 2021 04:08:22 -0800 (PST) Received: from localhost ([::1]:40754 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lEA0j-0007t1-2O for importer@patchew.org; Mon, 22 Feb 2021 07:08:21 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:41522) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lE9rx-0008Lk-OX for qemu-devel@nongnu.org; Mon, 22 Feb 2021 06:59:19 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:27027) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lE9rt-0001ag-LZ for qemu-devel@nongnu.org; Mon, 22 Feb 2021 06:59:17 -0500 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-557-TL3PbZm1Oae5JzZXvVlKog-1; Mon, 22 Feb 2021 06:59:11 -0500 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 531A786A061; Mon, 22 Feb 2021 11:59:10 +0000 (UTC) Received: from t480s.redhat.com (ovpn-115-16.ams2.redhat.com [10.36.115.16]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3F41719C45; Mon, 22 Feb 2021 11:58:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613995152; 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=/dPgg0Kyv23qQF1EHHOV47SNa3sxL4Q1rt18HZe6BYI=; b=hdYWszmRBTO4gdpaoPokpKxQ0pkXKM0sZgKUCefCSEfhpdBbRbnoK/W2dPhRcpfcDP6wNx 9GVyCegUB8YRtKA8GGOrtfjyAWJg//93unJ6AgeUOBhRLqwdUCGQni1jb7cawwe0o6mkmo 41wOSh9pwABdgBekquT72KaIau2KdWw= X-MC-Unique: TL3PbZm1Oae5JzZXvVlKog-1 From: David Hildenbrand To: qemu-devel@nongnu.org Subject: [PATCH v6 08/12] vfio: Support for RamDiscardMgr in the vIOMMU case Date: Mon, 22 Feb 2021 12:57:04 +0100 Message-Id: <20210222115708.7623-9-david@redhat.com> In-Reply-To: <20210222115708.7623-1-david@redhat.com> References: <20210222115708.7623-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=216.205.24.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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_LOW=-0.7, RCVD_IN_MSPIKE_H3=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: Pankaj Gupta , Wei Yang , "Michael S . Tsirkin" , David Hildenbrand , "Dr . David Alan Gilbert" , Peter Xu , Auger Eric , Alex Williamson , teawater , Igor Mammedov , Paolo Bonzini , Marek Kedzierski Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" vIOMMU support works already with RamDiscardMgr as long as guests only map populated memory. Both, populated and discarded memory is mapped into &address_space_memory, where vfio_get_xlat_addr() will find that memory, to create the vfio mapping. Sane guests will never map discarded memory (e.g., unplugged memory blocks in virtio-mem) into an IOMMU - or keep it mapped into an IOMMU while memory is getting discarded. However, there are two cases where a malicious guests could trigger pinning of more memory than intended. One case is easy to handle: the guest trying to map discarded memory into an IOMMU. The other case is harder to handle: the guest keeping memory mapped in the IOMMU while it is getting discarded. We would have to walk over all mappings when discarding memory and identify if any mapping would be a violation. Let's keep it simple for now and print a warning, indicating that setting RLIMIT_MEMLOCK can mitigate such attacks. We have to take care of incoming migration: at the point the IOMMUs get restored and start creating mappings in vfio, RamDiscardMgr implementations might not be back up and running yet: let's add runstate priorities to enforce the order when restoring. Acked-by: Alex Williamson Reviewed-by: Alex Williamson Acked-by: Michael S. Tsirkin Cc: Paolo Bonzini Cc: "Michael S. Tsirkin" Cc: Alex Williamson Cc: Dr. David Alan Gilbert Cc: Igor Mammedov Cc: Pankaj Gupta Cc: Peter Xu Cc: Auger Eric Cc: Wei Yang Cc: teawater Cc: Marek Kedzierski Signed-off-by: David Hildenbrand --- hw/vfio/common.c | 35 +++++++++++++++++++++++++++++++++++ hw/virtio/virtio-mem.c | 1 + include/migration/vmstate.h | 1 + 3 files changed, 37 insertions(+) diff --git a/hw/vfio/common.c b/hw/vfio/common.c index 166ec6ec62..15ecd05a4b 100644 --- a/hw/vfio/common.c +++ b/hw/vfio/common.c @@ -36,6 +36,7 @@ #include "qemu/range.h" #include "sysemu/kvm.h" #include "sysemu/reset.h" +#include "sysemu/runstate.h" #include "trace.h" #include "qapi/error.h" #include "migration/migration.h" @@ -574,6 +575,40 @@ static bool vfio_get_xlat_addr(IOMMUTLBEntry *iotlb, v= oid **vaddr, error_report("iommu map to non memory area %"HWADDR_PRIx"", xlat); return false; + } else if (memory_region_has_ram_discard_mgr(mr)) { + RamDiscardMgr *rdm =3D memory_region_get_ram_discard_mgr(mr); + RamDiscardMgrClass *rdmc =3D RAM_DISCARD_MGR_GET_CLASS(rdm); + + /* + * Malicious VMs can map memory into the IOMMU, which is expected + * to remain discarded. vfio will pin all pages, populating memory. + * Disallow that. vmstate priorities make sure any RamDiscardMgr w= ere + * already restored before IOMMUs are restored. + */ + if (!rdmc->is_populated(rdm, mr, xlat, len)) { + error_report("iommu map to discarded memory (e.g., unplugged v= ia" + " virtio-mem): %"HWADDR_PRIx"", + iotlb->translated_addr); + return false; + } + + /* + * Malicious VMs might trigger discarding of IOMMU-mapped memory. = The + * pages will remain pinned inside vfio until unmapped, resulting = in a + * higher memory consumption than expected. If memory would get + * populated again later, there would be an inconsistency between = pages + * pinned by vfio and pages seen by QEMU. This is the case until + * unmapped from the IOMMU (e.g., during device reset). + * + * With malicious guests, we really only care about pinning more m= emory + * than expected. RLIMIT_MEMLOCK set for the user/process can neve= r be + * exceeded and can be used to mitigate this problem. + */ + warn_report_once("Using vfio with vIOMMUs and coordinated discardi= ng of" + " RAM (e.g., virtio-mem) works, however, maliciou= s" + " guests can trigger pinning of more memory than" + " intended via an IOMMU. It's possible to mitigat= e " + " by setting/adjusting RLIMIT_MEMLOCK."); } =20 /* diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c index 3132e4b2b1..194fb56a9a 100644 --- a/hw/virtio/virtio-mem.c +++ b/hw/virtio/virtio-mem.c @@ -854,6 +854,7 @@ static const VMStateDescription vmstate_virtio_mem_devi= ce =3D { .name =3D "virtio-mem-device", .minimum_version_id =3D 1, .version_id =3D 1, + .priority =3D MIG_PRI_VIRTIO_MEM, .post_load =3D virtio_mem_post_load, .fields =3D (VMStateField[]) { VMSTATE_WITH_TMP(VirtIOMEM, VirtIOMEMMigSanityChecks, diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h index 075ee80096..3bf58ff043 100644 --- a/include/migration/vmstate.h +++ b/include/migration/vmstate.h @@ -153,6 +153,7 @@ typedef enum { MIG_PRI_DEFAULT =3D 0, MIG_PRI_IOMMU, /* Must happen before PCI devices */ MIG_PRI_PCI_BUS, /* Must happen before IOMMU */ + MIG_PRI_VIRTIO_MEM, /* Must happen before IOMMU */ MIG_PRI_GICV3_ITS, /* Must happen before PCI devices */ MIG_PRI_GICV3, /* Must happen before the ITS */ MIG_PRI_MAX, --=20 2.29.2