Re: [PATCH v2 1/2] vhost: Don't call access_ok() when using IOTLB

[Jason Wang <jasowang@redhat.com>]

On 2020/9/30 上午12:30, Greg Kurz wrote:
> When the IOTLB device is enabled, the vring addresses we get
> from userspace are GIOVAs. It is thus wrong to pass them down
> to access_ok() which only takes HVAs.
>
> Access validation is done at prefetch time with IOTLB. Teach
> vq_access_ok() about that by moving the (vq->iotlb) check
> from vhost_vq_access_ok() to vq_access_ok(). This prevents
> vhost_vring_set_addr() to fail when verifying the accesses.
> No behavior change for vhost_vq_access_ok().
>
> BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1883084
> Fixes: 6b1e6cc7855b ("vhost: new device IOTLB API")
> Cc: jasowang@redhat.com
> CC: stable@vger.kernel.org # 4.14+
> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---
>   drivers/vhost/vhost.c |    9 +++++----
>   1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index b45519ca66a7..c3b49975dc28 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1290,6 +1290,11 @@ static bool vq_access_ok(struct vhost_virtqueue *vq, unsigned int num,
>   			 vring_used_t __user *used)
>   
>   {
> +	/* If an IOTLB device is present, the vring addresses are
> +	 * GIOVAs. Access validation occurs at prefetch time. */
> +	if (vq->iotlb)
> +		return true;
> +
>   	return access_ok(desc, vhost_get_desc_size(vq, num)) &&
>   	       access_ok(avail, vhost_get_avail_size(vq, num)) &&
>   	       access_ok(used, vhost_get_used_size(vq, num));
> @@ -1383,10 +1388,6 @@ bool vhost_vq_access_ok(struct vhost_virtqueue *vq)
>   	if (!vq_log_access_ok(vq, vq->log_base))
>   		return false;
>   
> -	/* Access validation occurs at prefetch time with IOTLB */
> -	if (vq->iotlb)
> -		return true;
> -
>   	return vq_access_ok(vq, vq->num, vq->desc, vq->avail, vq->used);
>   }
>   EXPORT_SYMBOL_GPL(vhost_vq_access_ok);
>

Acked-by: Jason Wang <jasowang@redhat.com>

Thanks