diff mbox

[v3,03/10] virtio: stop virtqueue processing if device is broken

Message ID 1460467534-29147-4-git-send-email-stefanha@redhat.com (mailing list archive)
State New, archived
Headers show

Commit Message

Stefan Hajnoczi April 12, 2016, 1:25 p.m. UTC
QEMU prints an error message and exits when the device enters an invalid
state.  Terminating the process is heavy-handed.  The guest may still be
able to function even if there is a bug in a virtio guest driver.

Moreover, exiting is a bug in nested virtualization where a nested guest
could DoS other nested guests by killing a pass-through virtio device.
I don't think this configuration is possible today but it is likely in
the future.

If the broken flag is set, do not process virtqueues or write back used
descriptors.  The broken flag can be cleared again by resetting the
device.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 hw/virtio/virtio.c         | 39 +++++++++++++++++++++++++++++++++++++++
 include/hw/virtio/virtio.h |  3 +++
 2 files changed, 42 insertions(+)

Comments

Cornelia Huck Sept. 20, 2016, 11:35 a.m. UTC | #1
On Tue, 12 Apr 2016 14:25:27 +0100
Stefan Hajnoczi <stefanha@redhat.com> wrote:

> QEMU prints an error message and exits when the device enters an invalid
> state.  Terminating the process is heavy-handed.  The guest may still be
> able to function even if there is a bug in a virtio guest driver.
> 
> Moreover, exiting is a bug in nested virtualization where a nested guest
> could DoS other nested guests by killing a pass-through virtio device.
> I don't think this configuration is possible today but it is likely in
> the future.
> 
> If the broken flag is set, do not process virtqueues or write back used
> descriptors.  The broken flag can be cleared again by resetting the
> device.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  hw/virtio/virtio.c         | 39 +++++++++++++++++++++++++++++++++++++++
>  include/hw/virtio/virtio.h |  3 +++
>  2 files changed, 42 insertions(+)

Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
diff mbox

Patch

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 02c71a2..cedda4b 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -279,6 +279,10 @@  void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
 
     virtqueue_unmap_sg(vq, elem, len);
 
+    if (unlikely(vq->vdev->broken)) {
+        return;
+    }
+
     idx = (idx + vq->used_idx) % vq->vring.num;
 
     uelem.id = elem->index;
@@ -289,6 +293,12 @@  void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
 void virtqueue_flush(VirtQueue *vq, unsigned int count)
 {
     uint16_t old, new;
+
+    if (unlikely(vq->vdev->broken)) {
+        vq->inuse -= count;
+        return;
+    }
+
     /* Make sure buffer is written before we update index. */
     smp_wmb();
     trace_virtqueue_flush(vq, count);
@@ -549,6 +559,9 @@  void *virtqueue_pop(VirtQueue *vq, size_t sz)
     struct iovec iov[VIRTQUEUE_MAX_SIZE];
     VRingDesc desc;
 
+    if (unlikely(vdev->broken)) {
+        return NULL;
+    }
     if (virtio_queue_empty(vq)) {
         return NULL;
     }
@@ -708,6 +721,10 @@  static void virtio_notify_vector(VirtIODevice *vdev, uint16_t vector)
     BusState *qbus = qdev_get_parent_bus(DEVICE(vdev));
     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
 
+    if (unlikely(vdev->broken)) {
+        return;
+    }
+
     if (k->notify) {
         k->notify(qbus->parent, vector);
     }
@@ -791,6 +808,7 @@  void virtio_reset(void *opaque)
         k->reset(vdev);
     }
 
+    vdev->broken = false;
     vdev->guest_features = 0;
     vdev->queue_sel = 0;
     vdev->status = 0;
@@ -1104,6 +1122,10 @@  static void virtio_queue_notify_vq(VirtQueue *vq)
     if (vq->vring.desc && vq->handle_output) {
         VirtIODevice *vdev = vq->vdev;
 
+        if (unlikely(vdev->broken)) {
+            return;
+        }
+
         trace_virtio_queue_notify(vdev, vq - vdev->vq, vq);
         vq->handle_output(vdev, vq);
     }
@@ -1675,6 +1697,7 @@  void virtio_init(VirtIODevice *vdev, const char *name,
     vdev->config_vector = VIRTIO_NO_VECTOR;
     vdev->vq = g_malloc0(sizeof(VirtQueue) * VIRTIO_QUEUE_MAX);
     vdev->vm_running = runstate_is_running();
+    vdev->broken = false;
     for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
         vdev->vq[i].vector = VIRTIO_NO_VECTOR;
         vdev->vq[i].vdev = vdev;
@@ -1852,6 +1875,22 @@  void virtio_device_set_child_bus_name(VirtIODevice *vdev, char *bus_name)
     vdev->bus_name = g_strdup(bus_name);
 }
 
+void GCC_FMT_ATTR(2, 3) virtio_error(VirtIODevice *vdev, const char *fmt, ...)
+{
+    va_list ap;
+
+    va_start(ap, fmt);
+    error_vreport(fmt, ap);
+    va_end(ap);
+
+    vdev->broken = true;
+
+    if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) {
+        virtio_set_status(vdev, vdev->status | VIRTIO_CONFIG_S_NEEDS_RESET);
+        virtio_notify_config(vdev);
+    }
+}
+
 static void virtio_device_realize(DeviceState *dev, Error **errp)
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 6a37065..012b0d1 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -87,6 +87,7 @@  struct VirtIODevice
     VirtQueue *vq;
     uint16_t device_id;
     bool vm_running;
+    bool broken; /* device in invalid state, needs reset */
     VMChangeStateEntry *vmstate;
     char *bus_name;
     uint8_t device_endian;
@@ -135,6 +136,8 @@  void virtio_init(VirtIODevice *vdev, const char *name,
                          uint16_t device_id, size_t config_size);
 void virtio_cleanup(VirtIODevice *vdev);
 
+void virtio_error(VirtIODevice *vdev, const char *fmt, ...) GCC_FMT_ATTR(2, 3);
+
 /* Set the child bus name. */
 void virtio_device_set_child_bus_name(VirtIODevice *vdev, char *bus_name);