Subject: Re: [PATCH v3,net] virtio_net: Improve RSS key size validation

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 12 Feb 2026 09:40:49 -0500

On Thu, Feb 12, 2026 at 06:33:40PM +0530, Srujana Challa wrote:
> Replace hardcoded RSS max key size limit with a type based definition.
> Add validation for RSS key size against spec minimum (40 bytes). When
> validation fails, gracefully disable RSS features and continue
> initialization rather than failing completely.
> 
> Cc: [email-masked]
> Fixes: 3f7d9c1964fc ("virtio_net: Add hash_key_length check")
> Signed-off-by: Srujana Challa <[email-masked]>
> 
> v3:
> - Moved RSS key validation checks to virtnet_validate.
> - Add fixes: tag and CC -stable
> ---
>  drivers/net/virtio_net.c | 29 +++++++++++++++++++++--------
>  1 file changed, 21 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index db88dcaefb20..e61cea50dcab 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -381,7 +381,9 @@ struct receive_queue {
>  	struct xdp_buff **xsk_buffs;
>  };
>  
> -#define VIRTIO_NET_RSS_MAX_KEY_SIZE     40
> +#define VIRTIO_NET_RSS_MAX_KEY_SIZE \
> +	(type_max(((struct virtio_net_config *)0)->rss_max_key_size) + 1)

+1 here really unintuitive.
It does not look like it's still used, though?

> +#define VIRTIO_NET_RSS_MIN_KEY_SIZE 40
>  
>  /* Control VQ buffers: protected by the rtnl lock */
>  struct control_buf {
> @@ -6627,6 +6629,24 @@ static int virtnet_validate(struct virtio_device *vdev)
>  		__virtio_clear_bit(vdev, VIRTIO_NET_F_STANDBY);
>  	}
>  
> +	if (virtio_has_feature(vdev, VIRTIO_NET_F_RSS) ||
> +	    virtio_has_feature(vdev, VIRTIO_NET_F_HASH_REPORT)) {
> +		u8 key_sz = virtio_cread8(vdev,
> +					  offsetof(struct virtio_net_config,
> +						   rss_max_key_size));
> +		/* Spec requires at least 40 bytes */

move the define here then?

> +		if (key_sz < VIRTIO_NET_RSS_MIN_KEY_SIZE) {
> +			dev_warn(&vdev->dev,
> +				 "rss_max_key_size=%u is less than spec minimum %u, disabling RSS\n",
> +				 key_sz, VIRTIO_NET_RSS_MIN_KEY_SIZE);
> +			if (virtio_has_feature(vdev, VIRTIO_NET_F_RSS))
> +				__virtio_clear_bit(vdev, VIRTIO_NET_F_RSS);
> +			if (virtio_has_feature(vdev, VIRTIO_NET_F_HASH_REPORT))
> +				__virtio_clear_bit(vdev,
> +						   VIRTIO_NET_F_HASH_REPORT);

why not clear them unconditionally?

> +		}
> +	}
> +
>  	return 0;
>  }
>  
> @@ -6839,13 +6859,6 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	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));
> -		if (vi->rss_key_size > VIRTIO_NET_RSS_MAX_KEY_SIZE) {
> -			dev_err(&vdev->dev, "rss_max_key_size=%u exceeds the limit %u.\n",
> -				vi->rss_key_size, VIRTIO_NET_RSS_MAX_KEY_SIZE);
> -			err = -EINVAL;
> -			goto free;
> -		}
> -
>  		vi->rss_hash_types_supported =
>  		    virtio_cread32(vdev, offsetof(struct virtio_net_config, supported_hash_types));
>  		vi->rss_hash_types_supported &=
> -- 
> 2.25.1