Re: [PATCH v2 1/3] virtio_net: Preserve virtio header before XDP program execution

[Xuan Zhuo]

On Wed, 24 Jan 2024 16:57:19 +0800, Liang Chen <liangchen.linux@xxxxxxxxx> wrote:
> The xdp program may overwrite the inline virtio header. To ensure the
> integrity of the virtio header, it is saved in a data structure that
> wraps both the xdp_buff and the header before running the xdp program.
>
> Signed-off-by: Liang Chen <liangchen.linux@xxxxxxxxx>
> ---
>  drivers/net/virtio_net.c | 43 +++++++++++++++++++++++++++++-----------
>  1 file changed, 31 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index d7ce4a1011ea..b56828804e5f 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -349,6 +349,11 @@ struct virtio_net_common_hdr {
>  	};
>  };
>
> +struct virtnet_xdp_buff {
> +	struct xdp_buff xdp;
> +	struct virtio_net_common_hdr hdr;

Not all items of the hdr are useful, we can just save the useful items.

> +};
> +
>  static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf);
>
>  static bool is_xdp_frame(void *ptr)
> @@ -1199,9 +1204,10 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
>  	unsigned int headroom = vi->hdr_len + header_offset;
>  	struct virtio_net_hdr_mrg_rxbuf *hdr = buf + header_offset;
>  	struct page *page = virt_to_head_page(buf);
> +	struct virtnet_xdp_buff virtnet_xdp;
>  	struct page *xdp_page;
> +	struct xdp_buff *xdp;
>  	unsigned int buflen;
> -	struct xdp_buff xdp;
>  	struct sk_buff *skb;
>  	unsigned int metasize = 0;
>  	u32 act;
> @@ -1233,17 +1239,23 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
>  		page = xdp_page;
>  	}
>
> -	xdp_init_buff(&xdp, buflen, &rq->xdp_rxq);
> -	xdp_prepare_buff(&xdp, buf + VIRTNET_RX_PAD + vi->hdr_len,
> +	xdp = &virtnet_xdp.xdp;
> +	xdp_init_buff(xdp, buflen, &rq->xdp_rxq);
> +	xdp_prepare_buff(xdp, buf + VIRTNET_RX_PAD + vi->hdr_len,
>  			 xdp_headroom, len, true);
>
> -	act = virtnet_xdp_handler(xdp_prog, &xdp, dev, xdp_xmit, stats);
> +	/* Copy out the virtio header, as it may be overwritten by the
> +	 * xdp program.
> +	 */
> +	memcpy(&virtnet_xdp.hdr, hdr, vi->hdr_len);

Can we put this into virtnet_xdp_handler?

And just do that when the hash is negotiated.

> +
> +	act = virtnet_xdp_handler(xdp_prog, xdp, dev, xdp_xmit, stats);
>
>  	switch (act) {
>  	case XDP_PASS:
>  		/* Recalculate length in case bpf program changed it */
> -		len = xdp.data_end - xdp.data;
> -		metasize = xdp.data - xdp.data_meta;
> +		len = xdp->data_end - xdp->data;
> +		metasize = xdp->data - xdp->data_meta;
>  		break;
>
>  	case XDP_TX:
> @@ -1254,7 +1266,7 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
>  		goto err_xdp;
>  	}
>
> -	skb = virtnet_build_skb(buf, buflen, xdp.data - buf, len);
> +	skb = virtnet_build_skb(buf, buflen, xdp->data - buf, len);
>  	if (unlikely(!skb))
>  		goto err;
>
> @@ -1591,10 +1603,11 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
>  	int num_buf = virtio16_to_cpu(vi->vdev, hdr->num_buffers);
>  	struct page *page = virt_to_head_page(buf);
>  	int offset = buf - page_address(page);
> +	struct virtnet_xdp_buff virtnet_xdp;
>  	unsigned int xdp_frags_truesz = 0;
>  	struct sk_buff *head_skb;
>  	unsigned int frame_sz;
> -	struct xdp_buff xdp;
> +	struct xdp_buff *xdp;
>  	void *data;
>  	u32 act;
>  	int err;
> @@ -1604,16 +1617,22 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
>  	if (unlikely(!data))
>  		goto err_xdp;
>
> -	err = virtnet_build_xdp_buff_mrg(dev, vi, rq, &xdp, data, len, frame_sz,
> +	xdp = &virtnet_xdp.xdp;
> +	err = virtnet_build_xdp_buff_mrg(dev, vi, rq, xdp, data, len, frame_sz,
>  					 &num_buf, &xdp_frags_truesz, stats);
>  	if (unlikely(err))
>  		goto err_xdp;
>
> -	act = virtnet_xdp_handler(xdp_prog, &xdp, dev, xdp_xmit, stats);
> +	/* Copy out the virtio header, as it may be overwritten by the
> +	 * xdp program.
> +	 */
> +	memcpy(&virtnet_xdp.hdr, hdr, vi->hdr_len);
> +
> +	act = virtnet_xdp_handler(xdp_prog, xdp, dev, xdp_xmit, stats);
>
>  	switch (act) {
>  	case XDP_PASS:
> -		head_skb = build_skb_from_xdp_buff(dev, vi, &xdp, xdp_frags_truesz);
> +		head_skb = build_skb_from_xdp_buff(dev, vi, xdp, xdp_frags_truesz);
>  		if (unlikely(!head_skb))
>  			break;
>  		return head_skb;
> @@ -1626,7 +1645,7 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
>  		break;
>  	}
>
> -	put_xdp_frags(&xdp);
> +	put_xdp_frags(xdp);
>
>  err_xdp:
>  	put_page(page);
> --
> 2.40.1
>