Stefan Hajnoczi <stefa...@redhat.com> 于2020年9月17日周四 下午5:47写道：
>
> Fuzzing discovered that virtqueue_unmap_sg() is being called on modified
> req->in/out_sg iovecs. This means dma_memory_map() and
> dma_memory_unmap() calls do not have matching memory addresses.
>
> Fuzzing discovered that non-RAM addresses trigger a bug:
>
> void address_space_unmap(AddressSpace *as, void *buffer, hwaddr len,
> bool is_write, hwaddr access_len)
> {
> if (buffer != bounce.buffer) {
> ^^^^^^^^^^^^^^^^^^^^^^^
>
> A modified iov->iov_base is no longer recognized as a bounce buffer and
> the wrong branch is taken.
>
> There are more potential bugs: dirty memory is not tracked correctly and
> MemoryRegion refcounts can be leaked.
>
> Use the new iov_discard_undo() API to restore elem->in/out_sg before
> virtqueue_push() is called.
>
> Reported-by: Alexander Bulekov <alx...@bu.edu>
> Buglink: https://bugs.launchpad.net/qemu/+bug/1890360
> Fixes: 827805a2492c1bbf1c0712ed18ee069b4ebf3dd6 ("virtio-blk: Convert
> VirtIOBlockReq.out to structrue")
> Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
Reviewed-by: Li Qiang <liq...@gmail.com>
> ---
> include/hw/virtio/virtio-blk.h | 2 ++
> hw/block/virtio-blk.c | 11 +++++++++--
> 2 files changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
> index 29c9f32353..df3876d49c 100644
> --- a/include/hw/virtio/virtio-blk.h
> +++ b/include/hw/virtio/virtio-blk.h
> @@ -72,6 +72,8 @@ typedef struct VirtIOBlockReq {
> int64_t sector_num;
> VirtIOBlock *dev;
> VirtQueue *vq;
> + IOVDiscardUndo inhdr_undo;
> + IOVDiscardUndo outhdr_undo;
> struct virtio_blk_inhdr *in;
> struct virtio_blk_outhdr out;
> QEMUIOVector qiov;
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index 2204ba149e..bac2d6fa2b 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -80,6 +80,8 @@ static void virtio_blk_req_complete(VirtIOBlockReq *req,
> unsigned char status)
> trace_virtio_blk_req_complete(vdev, req, status);
>
> stb_p(&req->in->status, status);
> + iov_discard_undo(&req->inhdr_undo);
> + iov_discard_undo(&req->outhdr_undo);
> virtqueue_push(req->vq, &req->elem, req->in_len);
> if (s->dataplane_started && !s->dataplane_disabled) {
> virtio_blk_data_plane_notify(s->dataplane, req->vq);
> @@ -632,10 +634,12 @@ static int virtio_blk_handle_request(VirtIOBlockReq
> *req, MultiReqBuffer *mrb)
> return -1;
> }
>
> - iov_discard_front(&out_iov, &out_num, sizeof(req->out));
> + iov_discard_front_undoable(&out_iov, &out_num, sizeof(req->out),
> + &req->outhdr_undo);
>
> if (in_iov[in_num - 1].iov_len < sizeof(struct virtio_blk_inhdr)) {
> virtio_error(vdev, "virtio-blk request inhdr too short");
> + iov_discard_undo(&req->outhdr_undo);
> return -1;
> }
>
> @@ -644,7 +648,8 @@ static int virtio_blk_handle_request(VirtIOBlockReq *req,
> MultiReqBuffer *mrb)
> req->in = (void *)in_iov[in_num - 1].iov_base
> + in_iov[in_num - 1].iov_len
> - sizeof(struct virtio_blk_inhdr);
> - iov_discard_back(in_iov, &in_num, sizeof(struct virtio_blk_inhdr));
> + iov_discard_back_undoable(in_iov, &in_num, sizeof(struct
> virtio_blk_inhdr),
> + &req->inhdr_undo);
>
> type = virtio_ldl_p(vdev, &req->out.type);
>
> @@ -739,6 +744,8 @@ static int virtio_blk_handle_request(VirtIOBlockReq *req,
> MultiReqBuffer *mrb)
>
> if (unlikely(iov_to_buf(out_iov, out_num, 0, &dwz_hdr,
> sizeof(dwz_hdr)) != sizeof(dwz_hdr))) {
> + iov_discard_undo(&req->inhdr_undo);
> + iov_discard_undo(&req->outhdr_undo);
> virtio_error(vdev, "virtio-blk discard/write_zeroes header"
> " too short");
> return -1;
> --
> 2.26.2
>
