Re: [Qemu-devel] [PATCH v3 1/2] virtio: check VirtQueue Vring object is set

[Cornelia Huck]

On Sat, 25 Nov 2017 00:04:45 +0530
P J P <address@hidden> wrote:

> From: Prasad J Pandit <address@hidden>
> 
> An user could attempt to use an uninitialised VirtQueue object

s/An user/A guest/ ?

> or unset Vring.align leading to a arithmetic exception. Add check
> to avoid it.
> 
> Reported-by: Zhangboxian <address@hidden>
> Signed-off-by: Prasad J Pandit <address@hidden>
> ---
>  hw/virtio/virtio.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 5884ce3480..c01eac87a5 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -182,7 +182,7 @@ void virtio_queue_update_rings(VirtIODevice *vdev, int n)
>  {
>      VRing *vring = &vdev->vq[n].vring;
>  
> -    if (!vring->desc) {
> +    if (!vdev->vq[n].vring.num || !vring->desc || !vring->align) {
>          /* not yet setup -> nothing to do */
>          return;
>      }
> @@ -1414,6 +1414,9 @@ void virtio_config_modern_writel(VirtIODevice *vdev,
>  
>  void virtio_queue_set_addr(VirtIODevice *vdev, int n, hwaddr addr)
>  {
> +    if (!vdev->vq[n].vring.num) {
> +        return;
> +    }
>      vdev->vq[n].vring.desc = addr;
>      virtio_queue_update_rings(vdev, n);
>  }
> @@ -1426,6 +1429,9 @@ hwaddr virtio_queue_get_addr(VirtIODevice *vdev, int n)
>  void virtio_queue_set_rings(VirtIODevice *vdev, int n, hwaddr desc,
>                              hwaddr avail, hwaddr used)
>  {
> +    if (!vdev->vq[n].vring.num || !desc || !vdev->vq[n].vring.align) {


Checking for !desc is wrong (why shouldn't a driver be able to unset a
descriptor table?)

The check for align is not really needed, as virtio-1 disallows setting
align anyway.

> +        return;
> +    }
>      vdev->vq[n].vring.desc = desc;
>      vdev->vq[n].vring.avail = avail;
>      vdev->vq[n].vring.used = used;
> @@ -1494,8 +1500,10 @@ void virtio_queue_set_align(VirtIODevice *vdev, int n, 
> int align)
>       */
>      assert(k->has_variable_vring_alignment);
>  
> -    vdev->vq[n].vring.align = align;
> -    virtio_queue_update_rings(vdev, n);
> +    if (align) {
> +        vdev->vq[n].vring.align = align;
> +        virtio_queue_update_rings(vdev, n);
> +    }
>  }
>  
>  static bool virtio_queue_notify_aio_vq(VirtQueue *vq)