Re: [dpdk-dev] [PATCH v2] vhost: fix index overflow for packed ring in async vhost

["Xia, Chenbo" <chenbo.xia@intel.com>]

> -----Original Message-----
> From: Jiang, Cheng1 <cheng1.jiang@intel.com>
> Sent: Thursday, July 15, 2021 5:51 PM
> To: maxime.coquelin@redhat.com; Xia, Chenbo <chenbo.xia@intel.com>
> Cc: dev@dpdk.org; Hu, Jiayu <jiayu.hu@intel.com>; Yang, YvonneX
> <yvonnex.yang@intel.com>; Jiang, Cheng1 <cheng1.jiang@intel.com>;
> stable@dpdk.org
> Subject: [PATCH v2] vhost: fix index overflow for packed ring in async vhost
> 
> We introduced some new indexes in packed ring of async vhost. They
> will eventually overflow and lead to errors if the ring size is not
> a power of 2. This patch is to check and keep these indexes within a
> reasonable range.
> 
> Fixes: 873e8dad6f49 ("vhost: support packed ring in async datapath")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Cheng Jiang <cheng1.jiang@intel.com>
> ---
>  lib/vhost/virtio_net.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
> index f4a2c88d8b..bfb2bf8fc4 100644
> --- a/lib/vhost/virtio_net.c
> +++ b/lib/vhost/virtio_net.c
> @@ -2036,7 +2036,7 @@ virtio_dev_rx_async_submit_packed(struct virtio_net *dev,
> 
>  		slot_idx = (vq->async_pkts_idx + num_async_pkts) % vq->size;
>  		if (it_pool[it_idx].count) {
> -			uint16_t from, to;
> +			uint16_t from;
> 
>  			async_descs_idx += num_descs;
>  			async_fill_desc(&tdes[pkt_burst_idx++],
> @@ -2055,11 +2055,13 @@ virtio_dev_rx_async_submit_packed(struct virtio_net
> *dev,
>  			 * descriptors.
>  			 */
>  			from = vq->shadow_used_idx - num_buffers;
> -			to = vq->async_buffer_idx_packed % vq->size;
>  			store_dma_desc_info_packed(vq->shadow_used_packed,
> -					vq->async_buffers_packed, vq->size, from, to,
> num_buffers);
> +					vq->async_buffers_packed, vq->size, from,
> +					vq->async_buffer_idx_packed, num_buffers);
> 
>  			vq->async_buffer_idx_packed += num_buffers;
> +			if (vq->async_buffer_idx_packed >= vq->size)
> +				vq->async_buffer_idx_packed -= vq->size;
>  			vq->shadow_used_idx -= num_buffers;
>  		} else {
>  			comp_pkts[num_done_pkts++] = pkts[pkt_idx];
> @@ -2112,6 +2114,8 @@ virtio_dev_rx_async_submit_packed(struct virtio_net *dev,
>  		dma_error_handler_packed(vq, async_descs, async_descs_idx,
> slot_idx, pkt_err,
>  					&pkt_idx, &num_async_pkts, &num_done_pkts);
>  	vq->async_pkts_idx += num_async_pkts;
> +	if (vq->async_pkts_idx >= vq->size)
> +		vq->async_pkts_idx -= vq->size;
>  	*comp_count = num_done_pkts;
> 
>  	if (likely(vq->shadow_used_idx)) {
> @@ -2160,7 +2164,7 @@ write_back_completed_descs_packed(struct vhost_virtqueue
> *vq,
>  	uint16_t from, to;
> 
>  	do {
> -		from = vq->last_async_buffer_idx_packed % vq->size;
> +		from = vq->last_async_buffer_idx_packed;
>  		to = (from + nr_left) % vq->size;
>  		if (to > from) {
>  			vhost_update_used_packed(vq, vq->async_buffers_packed + from,
> to - from);
> @@ -2169,7 +2173,7 @@ write_back_completed_descs_packed(struct vhost_virtqueue
> *vq,
>  		} else {
>  			vhost_update_used_packed(vq, vq->async_buffers_packed + from,
>  				vq->size - from);
> -			vq->last_async_buffer_idx_packed += vq->size - from;
> +			vq->last_async_buffer_idx_packed = 0;
>  			nr_left -= vq->size - from;
>  		}
>  	} while (nr_left > 0);
> @@ -2252,10 +2256,13 @@ uint16_t rte_vhost_poll_enqueue_completed(int vid,
> uint16_t queue_id,
>  			vhost_vring_call_split(dev, vq);
>  		}
>  	} else {
> -		if (vq_is_packed(dev))
> +		if (vq_is_packed(dev)) {
>  			vq->last_async_buffer_idx_packed += n_buffers;
> -		else
> +			if (vq->last_async_buffer_idx_packed >= vq->size)
> +				vq->last_async_buffer_idx_packed -= vq->size;
> +		} else {
>  			vq->last_async_desc_idx_split += n_descs;
> +		}
>  	}
> 
>  done:
> --
> 2.29.2

Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>