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    Subject[ 19/80] virtio: force vring descriptors to be allocated from lowmem
    Date
    3.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Will Deacon <will.deacon@arm.com>

    commit b92b1b89a33c172c075edccf6afb0edc41d851fd upstream.

    Virtio devices may attempt to add descriptors to a virtqueue from atomic
    context using GFP_ATOMIC allocation. This is problematic because such
    allocations can fall outside of the lowmem mapping, causing virt_to_phys
    to report bogus physical addresses which are subsequently passed to
    userspace via the buffers for the virtual device.

    This patch masks out __GFP_HIGH and __GFP_HIGHMEM from the requested
    flags when allocating descriptors for a virtqueue. If an atomic
    allocation is requested and later fails, we will return -ENOSPC which
    will be handled by the driver.

    Signed-off-by: Will Deacon <will.deacon@arm.com>
    Cc: Sasha Levin <levinsasha928@gmail.com>
    Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/virtio/virtio_ring.c | 7 +++++++
    1 file changed, 7 insertions(+)

    --- a/drivers/virtio/virtio_ring.c
    +++ b/drivers/virtio/virtio_ring.c
    @@ -132,6 +132,13 @@ static int vring_add_indirect(struct vri
    unsigned head;
    int i;

    + /*
    + * We require lowmem mappings for the descriptors because
    + * otherwise virt_to_phys will give us bogus addresses in the
    + * virtqueue.
    + */
    + gfp &= ~(__GFP_HIGHMEM | __GFP_HIGH);
    +
    desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);
    if (!desc)
    return -ENOMEM;



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