virtio_mmio: Don't attempt to create empty virtqueues

If a virtio device reports a QueueNumMax of 0, vring_new_virtqueue()
doesn't check this, and thanks to an unsigned (i < num - 1) loop
guard, scribbles over memory when initialising the free list.

Avoid by not trying to create zero-descriptor queues, as there's no
way to do any I/O with one.

Signed-off-by: Brian Foley <brian.foley@arm.com>
Signed-off-by: Pawel Moll <pawel.moll@arm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 09edeec..6b1b7e1 100644 (file)
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -331,6 +331,16 @@ static struct virtqueue *vm_setup_vq(struct virtio_device *vdev, unsigned index,
         * and two rings (which makes it "alignment_size * 2")
         */
        info->num = readl(vm_dev->base + VIRTIO_MMIO_QUEUE_NUM_MAX);
+
+       /* If the device reports a 0 entry queue, we won't be able to
+        * use it to perform I/O, and vring_new_virtqueue() can't create
+        * empty queues anyway, so don't bother to set up the device.
+        */
+       if (info->num == 0) {
+               err = -ENOENT;
+               goto error_alloc_pages;
+       }
+
        while (1) {
                size = PAGE_ALIGN(vring_size(info->num,
                                VIRTIO_MMIO_VRING_ALIGN));