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Tsirkin" , Halil Pasic , Eric Farman , Richard Henderson , David Hildenbrand , Ilya Leoshkevich , Christian Borntraeger , Thomas Huth , "open list:virtio-ccw" Subject: Re: [PATCH v2] virtio: refresh vring region cache after updating a virtqueue size In-Reply-To: <20230317002749.27379-1-clopez@suse.de> Organization: Red Hat GmbH References: <20230317002749.27379-1-clopez@suse.de> User-Agent: Notmuch/0.37 (https://notmuchmail.org) Date: Wed, 22 Mar 2023 10:52:31 +0100 Message-ID: <87y1npglk0.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 Received-SPF: pass client-ip=170.10.129.124; envelope-from=cohuck@redhat.com; helo=us-smtp-delivery-124.mimecast.com 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_H2=-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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Fri, Mar 17 2023, Carlos L=C3=B3pez wrote: > When a virtqueue size is changed by the guest via > virtio_queue_set_num(), its region cache is not automatically updated. > If the size was increased, this could lead to accessing the cache out > of bounds. For example, in vring_get_used_event(): > > static inline uint16_t vring_get_used_event(VirtQueue *vq) > { > return vring_avail_ring(vq, vq->vring.num); > } > > static inline uint16_t vring_avail_ring(VirtQueue *vq, int i) > { > VRingMemoryRegionCaches *caches =3D vring_get_region_caches(vq); > hwaddr pa =3D offsetof(VRingAvail, ring[i]); > > if (!caches) { > return 0; > } > > return virtio_lduw_phys_cached(vq->vdev, &caches->avail, pa); > } > > vq->vring.num will be greater than caches->avail.len, which will > trigger a failed assertion down the call path of > virtio_lduw_phys_cached(). > > Fix this by calling virtio_init_region_cache() after > virtio_queue_set_num() if we are not already calling > virtio_queue_set_rings(). In the legacy path this is already done by > virtio_queue_update_rings(). > > Signed-off-by: Carlos L=C3=B3pez > --- > v2: use virtio_init_region_cache() instead of > virtio_queue_update_rings() in the path for modern devices. > > hw/s390x/virtio-ccw.c | 1 + > hw/virtio/virtio-mmio.c | 1 + > hw/virtio/virtio-pci.c | 1 + > hw/virtio/virtio.c | 2 +- > include/hw/virtio/virtio.h | 1 + > 5 files changed, 5 insertions(+), 1 deletion(-) > > diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c > index e33e5207ab..f44de1a8c1 100644 > --- a/hw/s390x/virtio-ccw.c > +++ b/hw/s390x/virtio-ccw.c > @@ -237,6 +237,7 @@ static int virtio_ccw_set_vqs(SubchDev *sch, VqInfoBl= ock *info, > return -EINVAL; > } > virtio_queue_set_num(vdev, index, num); > + virtio_init_region_cache(vdev, index); Hmm... this is not wrong, but looking at it again, I see that the guest has no way to change num after our last call to virtio_init_region_cache() (while setting up the queue addresses.) IOW, this introduces an extra round trip that is not really needed. > } else if (virtio_queue_get_num(vdev, index) > num) { > /* Fail if we don't have a big enough queue. */ > return -EINVAL; > diff --git a/hw/virtio/virtio-mmio.c b/hw/virtio/virtio-mmio.c > index 23ba625eb6..c2c6d85475 100644 > --- a/hw/virtio/virtio-mmio.c > +++ b/hw/virtio/virtio-mmio.c > @@ -354,6 +354,7 @@ static void virtio_mmio_write(void *opaque, hwaddr of= fset, uint64_t value, > if (proxy->legacy) { > virtio_queue_update_rings(vdev, vdev->queue_sel); > } else { > + virtio_init_region_cache(vdev, vdev->queue_sel); > proxy->vqs[vdev->queue_sel].num =3D value; > } > break; > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c > index 247325c193..02fb84a8fa 100644 > --- a/hw/virtio/virtio-pci.c > +++ b/hw/virtio/virtio-pci.c > @@ -1554,6 +1554,7 @@ static void virtio_pci_common_write(void *opaque, h= waddr addr, > proxy->vqs[vdev->queue_sel].num =3D val; > virtio_queue_set_num(vdev, vdev->queue_sel, > proxy->vqs[vdev->queue_sel].num); > + virtio_init_region_cache(vdev, vdev->queue_sel); > break; > case VIRTIO_PCI_COMMON_Q_MSIX: > vector =3D virtio_queue_vector(vdev, vdev->queue_sel); OTOH, all other transports need this call, as setting the addresses and setting num are two distinct operations. So I think we have two options: - apply your patch, and accept that we have the extra round trip for ccw (which should not really be an issue, we're processing a channel command anyway) - leave it out for ccw and add a comment why it isn't needed (I think I'd prefer to just go ahead with your patch.) Question (mostly for the other ccw folks): Do you think it is a problem that ccw sets up queue addresses and size via one command, while pci and mmio set addresses and size independently? I guess not; if anything, not setting them in one go may lead to issues like the one this patch is fixing.