Re: [PATCH 4.14 134/138] vhost: validate log when IOTLB is enabled

[Michael S. Tsirkin]

On Wed, Apr 11, 2018 at 12:25:24AM +0200, Greg Kroah-Hartman wrote:
> 4.14-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Jason Wang <jasowang@xxxxxxxxxx>
> 
> 
> [ Upstream commit d65026c6c62e7d9616c8ceb5a53b68bcdc050525 ]
> 
> Vq log_base is the userspace address of bitmap which has nothing to do
> with IOTLB. So it needs to be validated unconditionally otherwise we
> may try use 0 as log_base which may lead to pin pages that will lead
> unexpected result (e.g trigger BUG_ON() in set_bit_to_user()).
> 
> Fixes: 6b1e6cc7855b0 ("vhost: new device IOTLB API")
> Reported-by: syzbot+6304bf97ef436580fede@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
>  drivers/vhost/vhost.c |   14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
> 
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1252,14 +1252,12 @@ static int vq_log_access_ok(struct vhost
>  /* Caller should have vq mutex and device mutex */
>  int vhost_vq_access_ok(struct vhost_virtqueue *vq)
>  {
> -	if (vq->iotlb) {
> -		/* When device IOTLB was used, the access validation
> -		 * will be validated during prefetching.
> -		 */
> -		return 1;
> -	}
> -	return vq_access_ok(vq, vq->num, vq->desc, vq->avail, vq->used) &&
> -		vq_log_access_ok(vq, vq->log_base);
> +	int ret = vq_log_access_ok(vq, vq->log_base);
> +
> +	if (ret || vq->iotlb)

That's a bug, davem just queued a patch to fix this upstream.

> +		return ret;
> +
> +	return vq_access_ok(vq, vq->num, vq->desc, vq->avail, vq->used);
>  }
>  EXPORT_SYMBOL_GPL(vhost_vq_access_ok);
>  
>