Re: [PATCH net V2 1/4] vhost: make sure used idx is seen before log in vhost_add_used_n()

Michael S. Tsirkin
2018-12-12T14:33:40Z

On Wed, Dec 12, 2018 at 06:08:16PM +0800, Jason Wang wrote:
> We miss a write barrier that guarantees used idx is updated and seen
> before log. This will let userspace sync and copy used ring before
> used idx is update. Fix this by adding a barrier before log_write().
>
> Fixes: 8dd014adfea6f ("vhost-net: mergeable buffers support")
> Signed-off-by: Jason Wang <jasowang@redhat.com>

Acked-by: Michael S. Tsirkin <mst@redhat.com>

also for 4.20 and seems like a stable candidate.

> ---
> drivers/vhost/vhost.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 6b98d8e3a5bf..5915f240275a 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -2220,6 +2220,8 @@ int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,
> return -EFAULT;
> }
> if (unlikely(vq->log_used)) {
> + /* Make sure used idx is seen before log. */
> + smp_wmb();
> /* Log used index update. */
> log_write(vq->log_base,
> vq->log_addr + offsetof(struct vring_used, idx),
> --
> 2.17.1