On Mon, Sep 13, 2021 at 2:57 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > On Mon, Sep 13, 2021 at 02:40:09PM +0800, Jason Wang wrote: > > 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. > > That seems to suggest hwrng validation is better, and > I think it makes sense: will fix all rng drivers in one go. > > > > 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 > > My thinking is one just has to be aware that before enabling > any drivers they have to be audited. We can validate > used length but e.g. for virtio net the length is inside > the buffer anyway. Yes, maybe we can introduce a boolean to tell the virtio core that the driver can do the validation by itself. > > If we really have to, maybe use extra->len? The extra->len has already been used for per descriptor length. > And maybe have a mod param so the check can be turned off e.g. > for benchmarking purposes. Right. And I will benchmark the differences. 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
