Re: [RFC PATCH 17/17] virtio_ring: Add validation for used length

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, May 17, 2021 at 05:08:36PM +0800, Xie Yongji wrote:
> This adds validation for used length (might come
> from an untrusted device) when it will be used by
> virtio device driver.
> 
> Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
> ---
>  drivers/virtio/virtio_ring.c | 22 +++++++++++++++++++---
>  1 file changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index d999a1d6d271..7d4845d06f21 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -68,11 +68,13 @@
>  struct vring_desc_state_split {
>  	void *data;			/* Data for callback. */
>  	struct vring_desc *indir_desc;	/* Indirect descriptor, if any. */
> +	u32 in_len;			/* Total length of writable buffer */
>  };
>  
>  struct vring_desc_state_packed {
>  	void *data;			/* Data for callback. */
>  	struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */
> +	u32 in_len;			/* Total length of writable buffer */
>  	u16 num;			/* Descriptor list length. */
>  	u16 last;			/* The last desc state in a list. */
>  };


Hmm for packed it's aligned to 64 bit anyway, so we are not making it
any worse. But for split this pushes struct size up by 1/3 increasing
cache pressure.


> @@ -486,7 +488,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
>  	struct vring_virtqueue *vq = to_vvq(_vq);
>  	struct scatterlist *sg;
>  	struct vring_desc *desc;
> -	unsigned int i, n, avail, descs_used, prev, err_idx;
> +	unsigned int i, n, avail, descs_used, prev, err_idx, in_len = 0;
>  	int head;
>  	bool indirect;
>  
> @@ -570,6 +572,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
>  						     VRING_DESC_F_NEXT |
>  						     VRING_DESC_F_WRITE,
>  						     indirect);
> +			in_len += sg->length;
>  		}
>  	}
>  	/* Last one doesn't continue. */
> @@ -604,6 +607,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
>  
>  	/* Store token and indirect buffer state. */
>  	vq->split.desc_state[head].data = data;
> +	vq->split.desc_state[head].in_len = in_len;
>  	if (indirect)
>  		vq->split.desc_state[head].indir_desc = desc;
>  	else
> @@ -784,6 +788,10 @@ static void *virtqueue_get_buf_ctx_split(struct virtqueue *_vq,
>  		BAD_RING(vq, "id %u is not a head!\n", i);
>  		return NULL;
>  	}
> +	if (unlikely(len && vq->split.desc_state[i].in_len < *len)) {
> +		BAD_RING(vq, "id %u has invalid length: %u!\n", i, *len);
> +		return NULL;
> +	}
>  
>  	/* detach_buf_split clears data, so grab it now. */
>  	ret = vq->split.desc_state[i].data;
> @@ -1059,7 +1067,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
>  {
>  	struct vring_packed_desc *desc;
>  	struct scatterlist *sg;
> -	unsigned int i, n, err_idx;
> +	unsigned int i, n, err_idx, in_len = 0;
>  	u16 head, id;
>  	dma_addr_t addr;
>  
> @@ -1084,6 +1092,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
>  			if (vring_mapping_error(vq, addr))
>  				goto unmap_release;
>  
> +			in_len += (n < out_sgs) ? 0 : sg->length;
>  			desc[i].flags = cpu_to_le16(n < out_sgs ?
>  						0 : VRING_DESC_F_WRITE);
>  			desc[i].addr = cpu_to_le64(addr);
> @@ -1141,6 +1150,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
>  	vq->packed.desc_state[id].data = data;
>  	vq->packed.desc_state[id].indir_desc = desc;
>  	vq->packed.desc_state[id].last = id;
> +	vq->packed.desc_state[id].in_len = in_len;
>  
>  	vq->num_added += 1;
>  
> @@ -1173,7 +1183,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
>  	struct vring_virtqueue *vq = to_vvq(_vq);
>  	struct vring_packed_desc *desc;
>  	struct scatterlist *sg;
> -	unsigned int i, n, c, descs_used, err_idx;
> +	unsigned int i, n, c, descs_used, err_idx, in_len = 0;
>  	__le16 head_flags, flags;
>  	u16 head, id, prev, curr, avail_used_flags;
>  
> @@ -1223,6 +1233,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
>  			if (vring_mapping_error(vq, addr))
>  				goto unmap_release;
>  
> +			in_len += (n < out_sgs) ? 0 : sg->length;
>  			flags = cpu_to_le16(vq->packed.avail_used_flags |
>  				    (++c == total_sg ? 0 : VRING_DESC_F_NEXT) |
>  				    (n < out_sgs ? 0 : VRING_DESC_F_WRITE));
> @@ -1268,6 +1279,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
>  	vq->packed.desc_state[id].data = data;
>  	vq->packed.desc_state[id].indir_desc = ctx;
>  	vq->packed.desc_state[id].last = prev;
> +	vq->packed.desc_state[id].in_len = in_len;
>  
>  	/*
>  	 * A driver MUST NOT make the first descriptor in the list
> @@ -1456,6 +1468,10 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq,
>  		BAD_RING(vq, "id %u is not a head!\n", id);
>  		return NULL;
>  	}
> +	if (unlikely(len && vq->packed.desc_state[id].in_len < *len)) {
> +		BAD_RING(vq, "id %u has invalid length: %u!\n", id, *len);
> +		return NULL;
> +	}
>  
>  	/* detach_buf_packed clears data, so grab it now. */
>  	ret = vq->packed.desc_state[id].data;
> -- 
> 2.11.0

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