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

[Jason Wang]

在 2021/5/18 上午7:39, Michael S. Tsirkin 写道:
> 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@xxxxxxxxxxxxx>
> > ---
> >   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.


We can eliminate this by validating through virtio device driver instead 
of virtio core.

E.g for virtio-net we know the rx buffer size so there's no need to 
store in twice in the core.

Thanks


> > @@ -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