From nobody Sat Nov 15 16:45:33 2025 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; 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 Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1750787665223434.8869830552708; Tue, 24 Jun 2025 10:54:25 -0700 (PDT) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uU7ps-0002tD-Ib; Tue, 24 Jun 2025 13:53:33 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uU7pm-0002rt-Jv; Tue, 24 Jun 2025 13:53:26 -0400 Received: from vps-ovh.mhejs.net ([145.239.82.108]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uU7pk-0002in-J1; Tue, 24 Jun 2025 13:53:26 -0400 Received: from MUA by vps-ovh.mhejs.net with esmtpsa (TLS1.3) tls TLS_AES_256_GCM_SHA384 (Exim 4.98.1) (envelope-from ) id 1uU7pb-00000005WmI-1ZgI; Tue, 24 Jun 2025 19:53:15 +0200 From: "Maciej S. Szmigiero" To: Alex Williamson , =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= , Peter Xu , Fabiano Rosas Cc: Peter Maydell , Avihai Horon , qemu-arm@nongnu.org, qemu-devel@nongnu.org Subject: [PATCH 1/3] vfio/migration: Max in-flight VFIO device state buffer count limit Date: Tue, 24 Jun 2025 19:51:56 +0200 Message-ID: <0e88a253e06647f6c01bdeba45848501b3631bd3.1750787338.git.maciej.szmigiero@oracle.com> X-Mailer: git-send-email 2.49.0 In-Reply-To: References: MIME-Version: 1.0 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=145.239.82.108; envelope-from=mhej@vps-ovh.mhejs.net; helo=vps-ovh.mhejs.net X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZM-MESSAGEID: 1750787668478116600 Content-Type: text/plain; charset="utf-8" From: "Maciej S. Szmigiero" Allow capping the maximum count of in-flight VFIO device state buffers queued at the destination, otherwise a malicious QEMU source could theoretically cause the target QEMU to allocate unlimited amounts of memory for buffers-in-flight. Since this is not expected to be a realistic threat in most of VFIO live migration use cases and the right value depends on the particular setup disable the limit by default by setting it to UINT64_MAX. Signed-off-by: Maciej S. Szmigiero Reviewed-by: Avihai Horon Reviewed-by: Fabiano Rosas --- docs/devel/migration/vfio.rst | 13 +++++++++++++ hw/vfio/migration-multifd.c | 16 ++++++++++++++++ hw/vfio/pci.c | 9 +++++++++ include/hw/vfio/vfio-device.h | 1 + 4 files changed, 39 insertions(+) diff --git a/docs/devel/migration/vfio.rst b/docs/devel/migration/vfio.rst index 673e354754c8..f4a6bfa4619b 100644 --- a/docs/devel/migration/vfio.rst +++ b/docs/devel/migration/vfio.rst @@ -247,3 +247,16 @@ The multifd VFIO device state transfer is controlled by "x-migration-multifd-transfer" VFIO device property. This property default= s to AUTO, which means that VFIO device state transfer via multifd channels is attempted in configurations that otherwise support it. + +Since the target QEMU needs to load device state buffers in-order it needs= to +queue incoming buffers until they can be loaded into the device. +This means that a malicious QEMU source could theoretically cause the targ= et +QEMU to allocate unlimited amounts of memory for such buffers-in-flight. + +The "x-migration-max-queued-buffers" property allows capping the maximum c= ount +of these VFIO device state buffers queued at the destination. + +Because a malicious QEMU source causing OOM on the target is not expected = to be +a realistic threat in most of VFIO live migration use cases and the right = value +depends on the particular setup by default this queued buffers limit is +disabled by setting it to UINT64_MAX. diff --git a/hw/vfio/migration-multifd.c b/hw/vfio/migration-multifd.c index 850a31948878..f26c112090b4 100644 --- a/hw/vfio/migration-multifd.c +++ b/hw/vfio/migration-multifd.c @@ -56,6 +56,7 @@ typedef struct VFIOMultifd { QemuMutex load_bufs_mutex; /* Lock order: this lock -> BQL */ uint32_t load_buf_idx; uint32_t load_buf_idx_last; + uint32_t load_buf_queued_pending_buffers; } VFIOMultifd; =20 static void vfio_state_buffer_clear(gpointer data) @@ -127,6 +128,17 @@ static bool vfio_load_state_buffer_insert(VFIODevice *= vbasedev, =20 assert(packet->idx >=3D multifd->load_buf_idx); =20 + multifd->load_buf_queued_pending_buffers++; + if (multifd->load_buf_queued_pending_buffers > + vbasedev->migration_max_queued_buffers) { + error_setg(errp, + "%s: queuing state buffer %" PRIu32 + " would exceed the max of %" PRIu64, + vbasedev->name, packet->idx, + vbasedev->migration_max_queued_buffers); + return false; + } + lb->data =3D g_memdup2(&packet->data, packet_total_size - sizeof(*pack= et)); lb->len =3D packet_total_size - sizeof(*packet); lb->is_present =3D true; @@ -387,6 +399,9 @@ static bool vfio_load_bufs_thread(void *opaque, bool *s= hould_quit, Error **errp) goto thread_exit; } =20 + assert(multifd->load_buf_queued_pending_buffers > 0); + multifd->load_buf_queued_pending_buffers--; + if (multifd->load_buf_idx =3D=3D multifd->load_buf_idx_last - 1) { trace_vfio_load_state_device_buffer_end(vbasedev->name); } @@ -423,6 +438,7 @@ static VFIOMultifd *vfio_multifd_new(void) =20 multifd->load_buf_idx =3D 0; multifd->load_buf_idx_last =3D UINT32_MAX; + multifd->load_buf_queued_pending_buffers =3D 0; qemu_cond_init(&multifd->load_bufs_buffer_ready_cond); =20 multifd->load_bufs_thread_running =3D false; diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c index fa25bded25c5..2765a39f9df1 100644 --- a/hw/vfio/pci.c +++ b/hw/vfio/pci.c @@ -3524,6 +3524,8 @@ static const Property vfio_pci_dev_properties[] =3D { vbasedev.migration_multifd_transfer, vfio_pci_migration_multifd_transfer_prop, OnOffAuto, .set_default =3D true, .defval.i =3D ON_OFF_AUTO_AUTO), + DEFINE_PROP_UINT64("x-migration-max-queued-buffers", VFIOPCIDevice, + vbasedev.migration_max_queued_buffers, UINT64_MAX), DEFINE_PROP_BOOL("migration-events", VFIOPCIDevice, vbasedev.migration_events, false), DEFINE_PROP_BOOL("x-no-mmap", VFIOPCIDevice, vbasedev.no_mmap, false), @@ -3698,6 +3700,13 @@ static void vfio_pci_dev_class_init(ObjectClass *kla= ss, const void *data) "x-migration-multifd-transfer", "Transfer this device state via " "multifd channels when live migr= ating it"); + object_class_property_set_description(klass, /* 10.1 */ + "x-migration-max-queued-buffers", + "Maximum count of in-flight VFIO= " + "device state buffers queued at = the " + "destination when doing live " + "migration of device state via " + "multifd channels"); } =20 static const TypeInfo vfio_pci_dev_info =3D { diff --git a/include/hw/vfio/vfio-device.h b/include/hw/vfio/vfio-device.h index d45e5a68a24e..0ee34aaf668b 100644 --- a/include/hw/vfio/vfio-device.h +++ b/include/hw/vfio/vfio-device.h @@ -66,6 +66,7 @@ typedef struct VFIODevice { bool ram_block_discard_allowed; OnOffAuto enable_migration; OnOffAuto migration_multifd_transfer; + uint64_t migration_max_queued_buffers; bool migration_events; bool use_region_fds; VFIODeviceOps *ops;