On Mon, Sep 13, 2021 at 2:36 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > On Mon, Sep 13, 2021 at 01:53:53PM +0800, Jason Wang wrote: > > This patch validate the used buffer length provided by the device > > before trying to use it. This is done by record the in buffer length > > in a new field in desc_state structure during virtqueue_add(), then we > > can fail the virtqueue_get_buf() when we find the device is trying to > > give us a used buffer length which is greater than the in buffer > > length. > > > > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx> > > Hmm this was proposed in the past. The overhead here is > not negligeable, so I'd like to know more - > when is it a problem if the used len is too big? One example is: https://github.com/fuzzsa/fuzzsa-bugs/blob/master/virtio_rng.md And there would be more I guess. > Don't the affected drivers already track the length somewhere > and so can validated it without the extra cost in > virtio core? Probably, but this requires the changes in each device driver. And it would be easily forgotten if new drivers are introduced? Thanks > > > --- > > drivers/virtio/virtio_ring.c | 23 +++++++++++++++++++++++ > > 1 file changed, 23 insertions(+) > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > index d2ca0a7365f8..b8374a6144f3 100644 > > --- a/drivers/virtio/virtio_ring.c > > +++ b/drivers/virtio/virtio_ring.c > > @@ -69,6 +69,7 @@ > > struct vring_desc_state_split { > > void *data; /* Data for callback. */ > > struct vring_desc *indir_desc; /* Indirect descriptor, if any. */ > > + u64 buflen; /* In buffer length */ > > }; > > > > struct vring_desc_state_packed { > > @@ -76,6 +77,7 @@ struct vring_desc_state_packed { > > struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */ > > u16 num; /* Descriptor list length. */ > > u16 last; /* The last desc state in a list. */ > > + u64 buflen; /* In buffer length */ > > }; > > > > struct vring_desc_extra { > > @@ -490,6 +492,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq, > > unsigned int i, n, avail, descs_used, prev, err_idx; > > int head; > > bool indirect; > > + u64 buflen = 0; > > > > START_USE(vq); > > > > @@ -571,6 +574,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq, > > VRING_DESC_F_NEXT | > > VRING_DESC_F_WRITE, > > indirect); > > + buflen += sg->length; > > } > > } > > /* Last one doesn't continue. */ > > @@ -605,6 +609,7 @@ 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].buflen = buflen; > > if (indirect) > > vq->split.desc_state[head].indir_desc = desc; > > else > > @@ -784,6 +789,11 @@ 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].buflen)) { > > + BAD_RING(vq, "used len %d is larger than in buflen %lld\n", > > + *len, vq->split.desc_state[i].buflen); > > + return NULL; > > + } > > > > /* detach_buf_split clears data, so grab it now. */ > > ret = vq->split.desc_state[i].data; > > @@ -1062,6 +1072,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq, > > unsigned int i, n, err_idx; > > u16 head, id; > > dma_addr_t addr; > > + u64 buflen = 0; > > > > head = vq->packed.next_avail_idx; > > desc = alloc_indirect_packed(total_sg, gfp); > > @@ -1089,6 +1100,8 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq, > > desc[i].addr = cpu_to_le64(addr); > > desc[i].len = cpu_to_le32(sg->length); > > i++; > > + if (n >= out_sgs) > > + buflen += sg->length; > > } > > } > > > > @@ -1141,6 +1154,7 @@ 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].buflen = buflen; > > > > vq->num_added += 1; > > > > @@ -1176,6 +1190,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq, > > unsigned int i, n, c, descs_used, err_idx; > > __le16 head_flags, flags; > > u16 head, id, prev, curr, avail_used_flags; > > + u64 buflen = 0; > > > > START_USE(vq); > > > > @@ -1250,6 +1265,8 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq, > > 1 << VRING_PACKED_DESC_F_AVAIL | > > 1 << VRING_PACKED_DESC_F_USED; > > } > > + if (n >= out_sgs) > > + buflen += sg->length; > > } > > } > > > > @@ -1268,6 +1285,7 @@ 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].buflen = buflen; > > > > /* > > * A driver MUST NOT make the first descriptor in the list > > @@ -1455,6 +1473,11 @@ 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].buflen)) { > > + BAD_RING(vq, "used len %d is larger than in buflen %lld\n", > > + *len, vq->packed.desc_state[id].buflen); > > + return NULL; > > + } > > > > /* detach_buf_packed clears data, so grab it now. */ > > ret = vq->packed.desc_state[id].data; > > -- > > 2.25.1 > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
