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virtio: refresh vring region cache after updating a virtqueue size

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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_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 López <clopez@suse.de>
Message-Id: <20230317002749.27379-1-clopez@suse.de>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Acked-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Carlos López 2023-03-17 01:27:51 +01:00 committed by Michael S. Tsirkin
parent c1eb2ddf0f
commit f0d634ea19
5 changed files with 5 additions and 1 deletions
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1
hw/s390x/virtio-ccw.c
View file

@ -237,6 +237,7 @@ static int virtio_ccw_set_vqs(SubchDev *sch, VqInfoBlock *info,
return -EINVAL;
}
virtio_queue_set_num(vdev, index, num);
virtio_init_region_cache(vdev, index);
} else if (virtio_queue_get_num(vdev, index) > num) {
/* Fail if we don't have a big enough queue. */
return -EINVAL;

1
hw/virtio/virtio-mmio.c
View file

@ -354,6 +354,7 @@ static void virtio_mmio_write(void *opaque, hwaddr offset, 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 = value;
}
break;

1
hw/virtio/virtio-pci.c
View file

@ -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_init_region_cache(vdev, vdev->queue_sel);
break;
case VIRTIO_PCI_COMMON_Q_MSIX:
vector = virtio_queue_vector(vdev, vdev->queue_sel);

2
hw/virtio/virtio.c
View file

@ -226,7 +226,7 @@ static void virtio_virtqueue_reset_region_cache(struct VirtQueue *vq)
}
}
static void virtio_init_region_cache(VirtIODevice *vdev, int n)
void virtio_init_region_cache(VirtIODevice *vdev, int n)
{
VirtQueue *vq = &vdev->vq[n];
VRingMemoryRegionCaches *old = vq->vring.caches;

1
include/hw/virtio/virtio.h
View file

@ -309,6 +309,7 @@ int virtio_get_num_queues(VirtIODevice *vdev);
void virtio_queue_set_rings(VirtIODevice *vdev, int n, hwaddr desc,
hwaddr avail, hwaddr used);
void virtio_queue_update_rings(VirtIODevice *vdev, int n);
void virtio_init_region_cache(VirtIODevice *vdev, int n);
void virtio_queue_set_align(VirtIODevice *vdev, int n, int align);
void virtio_queue_notify(VirtIODevice *vdev, int n);
uint16_t virtio_queue_vector(VirtIODevice *vdev, int n);