Untrusted device support for virtio

Hi All:

Sometimes, the driver doesn't trust the device. This is usually
happens for the encrtpyed VM or VDUSE[1]. In both cases, technology
like swiotlb is used to prevent the poking/mangling of memory from the
device. But this is not sufficient since current virtio driver may
trust what is stored in the descriptor table (coherent mapping) for
performing the DMA operations like unmap and bounce so the device may
choose to utilize the behaviour of swiotlb to perform attacks[2].

For double insurance, to protect from a malicous device, when DMA API
is used for the device, this series store and use the descriptor
metadata in an auxiliay structure which can not be accessed via
swiotlb instead of the ones in the descriptor table. Actually, we've
almost achieved that through packed virtqueue and we just need to fix
a corner case of handling mapping errors. For split virtqueue we just
follow what's done in the packed.

Note that we don't duplicate descriptor medata for indirect
descriptors since it uses stream mapping which is read only so it's
safe if the metadata of non-indirect descriptors are correct.

The behaivor for non DMA API is kept for minimizing the performance
impact.

Slightly tested with packed on/off, iommu on/of, swiotlb force/off in
the guest.

Please review.

[1] https://lore.kernel.org/netdev/fab615ce-5e13-a3b3-3715-a4...
[2] https://yhbt.net/lore/all/c3629a27-3590-1d9f-211b-c0b7be1...

Jason Wang (7):
  virtio-ring: maintain next in extra state for packed virtqueue
  virtio_ring: rename vring_desc_extra_packed
  virtio-ring: factor out desc_extra allocation
  virtio_ring: secure handling of mapping errors
  virtio_ring: introduce virtqueue_desc_add_split()
  virtio: use err label in __vring_new_virtqueue()
  virtio-ring: store DMA metadata in desc_extra for split virtqueue

 drivers/virtio/virtio_ring.c | 189 ++++++++++++++++++++++++++---------
 1 file changed, 141 insertions(+), 48 deletions(-)

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2.25.1