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Re: [PATCH] virtio: refresh vring region cache after updating a virtqueu
From: |
Cornelia Huck |
Subject: |
Re: [PATCH] virtio: refresh vring region cache after updating a virtqueue size |
Date: |
Thu, 09 Mar 2023 11:43:46 +0100 |
User-agent: |
Notmuch/0.37 (https://notmuchmail.org) |
On Thu, Mar 02 2023, Carlos López <clopez@suse.de> 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.
>
> Signed-off-by: Carlos López <clopez@suse.de>
> ---
> 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);