On Thu, Mar 09, 2023 at 11:43:46AM +0100, Cornelia Huck wrote: > On Thu, Mar 02 2023, Carlos López <[email protected]> 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 = vring_get_region_caches(vq); > > hwaddr pa = 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_queue_update_rings() after > > virtio_queue_set_num() if we are not already calling > > virtio_queue_set_rings(). > > Don't we instead need to call virtio_init_region_cache() to update the > caches? virtio_queue_set_rings() will calculate avail and used from > desc, which looks wrong for modern devices.
Carlos? > > > > Signed-off-by: Carlos López <[email protected]> > > --- > > hw/s390x/virtio-ccw.c | 1 + > > hw/virtio/virtio-mmio.c | 5 ++--- > > hw/virtio/virtio-pci.c | 1 + > > 3 files changed, 4 insertions(+), 3 deletions(-) > > > > diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c > > index e33e5207ab..89891ac58a 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, > > VqInfoBlock *info, > > return -EINVAL; > > } > > virtio_queue_set_num(vdev, index, num); > > + virtio_queue_update_rings(vdev, index); > > Note that this is the non-legacy path. > > > } 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..c74822308f 100644 > > --- a/hw/virtio/virtio-mmio.c > > +++ b/hw/virtio/virtio-mmio.c > > @@ -350,10 +350,9 @@ static void virtio_mmio_write(void *opaque, hwaddr > > offset, uint64_t value, > > case VIRTIO_MMIO_QUEUE_NUM: > > trace_virtio_mmio_queue_write(value, VIRTQUEUE_MAX_SIZE); > > virtio_queue_set_num(vdev, vdev->queue_sel, value); > > + virtio_queue_update_rings(vdev, vdev->queue_sel); > > > > - if (proxy->legacy) { > > - virtio_queue_update_rings(vdev, vdev->queue_sel); > > - } else { > > + if (!proxy->legacy) { > > proxy->vqs[vdev->queue_sel].num = value; > > } > > break; > > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c > > index 247325c193..a0a2f2c965 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, > > hwaddr addr, > > proxy->vqs[vdev->queue_sel].num = val; > > virtio_queue_set_num(vdev, vdev->queue_sel, > > proxy->vqs[vdev->queue_sel].num); > > + virtio_queue_update_rings(vdev, vdev->queue_sel); > > break; > > case VIRTIO_PCI_COMMON_Q_MSIX: > > vector = virtio_queue_vector(vdev, vdev->queue_sel);
