Commit 059a49aa authored Apr 03, 2024 by Breno Leitao Committed by David S. Miller Apr 07, 2024

virtio_net: Do not send RSS key if it is not supported



There is a bug when setting the RSS options in virtio_net that can break
the whole machine, getting the kernel into an infinite loop.

Running the following command in any QEMU virtual machine with virtionet
will reproduce this problem:

    # ethtool -X eth0  hfunc toeplitz

This is how the problem happens:

1) ethtool_set_rxfh() calls virtnet_set_rxfh()

2) virtnet_set_rxfh() calls virtnet_commit_rss_command()

3) virtnet_commit_rss_command() populates 4 entries for the rss
scatter-gather

4) Since the command above does not have a key, then the last
scatter-gatter entry will be zeroed, since rss_key_size == 0.
sg_buf_size = vi->rss_key_size;

5) This buffer is passed to qemu, but qemu is not happy with a buffer
with zero length, and do the following in virtqueue_map_desc() (QEMU
function):

  if (!sz) {
      virtio_error(vdev, "virtio: zero sized buffers are not allowed");

6) virtio_error() (also QEMU function) set the device as broken

    vdev->broken = true;

7) Qemu bails out, and do not repond this crazy kernel.

8) The kernel is waiting for the response to come back (function
virtnet_send_command())

9) The kernel is waiting doing the following :

      while (!virtqueue_get_buf(vi->cvq, &tmp) &&
	     !virtqueue_is_broken(vi->cvq))
	      cpu_relax();

10) None of the following functions above is true, thus, the kernel
loops here forever. Keeping in mind that virtqueue_is_broken() does
not look at the qemu `vdev->broken`, so, it never realizes that the
vitio is broken at QEMU side.

Fix it by not sending RSS commands if the feature is not available in
the device.

Fixes: c7114b12 ("drivers/net/virtio_net: Added basic RSS support.")
Cc: stable@vger.kernel.org
Cc: qemu-devel@nongnu.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Heng Qi <hengqi@linux.alibaba.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 237f3cf1

drivers/net/virtio_net.c

+22 −4

Original line number	Diff line number	Diff line
		@@ -3807,6 +3807,7 @@ static int virtnet_set_rxfh(struct net_device *dev,
		struct netlink_ext_ack *extack)
		{
		struct virtnet_info *vi = netdev_priv(dev);
		bool update = false;
		int i;

		if (rxfh->hfunc != ETH_RSS_HASH_NO_CHANGE &&
		@@ -3814,12 +3815,27 @@ static int virtnet_set_rxfh(struct net_device *dev,
		return -EOPNOTSUPP;

		if (rxfh->indir) {
		if (!vi->has_rss)
		return -EOPNOTSUPP;

		for (i = 0; i < vi->rss_indir_table_size; ++i)
		vi->ctrl->rss.indirection_table[i] = rxfh->indir[i];
		update = true;
		}
		if (rxfh->key)

		if (rxfh->key) {
		/* If either _F_HASH_REPORT or _F_RSS are negotiated, the
		* device provides hash calculation capabilities, that is,
		* hash_key is configured.
		*/
		if (!vi->has_rss && !vi->has_rss_hash_report)
		return -EOPNOTSUPP;

		memcpy(vi->ctrl->rss.key, rxfh->key, vi->rss_key_size);
		update = true;
		}

		if (update)
		virtnet_commit_rss_command(vi);

		return 0;
		@@ -4729,13 +4745,15 @@ static int virtnet_probe(struct virtio_device *vdev)
		if (virtio_has_feature(vdev, VIRTIO_NET_F_HASH_REPORT))
		vi->has_rss_hash_report = true;

		if (virtio_has_feature(vdev, VIRTIO_NET_F_RSS))
		if (virtio_has_feature(vdev, VIRTIO_NET_F_RSS)) {
		vi->has_rss = true;

		if (vi->has_rss \|\| vi->has_rss_hash_report) {
		vi->rss_indir_table_size =
		virtio_cread16(vdev, offsetof(struct virtio_net_config,
		rss_max_indirection_table_length));
		}

		if (vi->has_rss \|\| vi->has_rss_hash_report) {
		vi->rss_key_size =
		virtio_cread8(vdev, offsetof(struct virtio_net_config, rss_max_key_size));