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

Jason Wang Mon, 24 May 2021 18:32:03 -0700


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 <[email protected]>
---
  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 insteadof virtio core.

E.g for virtio-net we know the rx buffer size so there's no need tostore 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


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

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