mirror of
https://github.com/cloud-hypervisor/cloud-hypervisor.git
synced 2026-08-05 02:19:16 +00:00
Peter Oskolkov
7696bcc71f
A buggy or malicious guest may write an inappropriate value into
virtqueue's next_avail field. This will result in an error
when iterating over the queue:
https://github.com/rust-vmm/vm-virtio/blob/863837ef863f6880bb8357e60bbac49e72c0844c/virtio-queue/src/queue.rs#L708
but this error is (logged and) ignored if pop_descriptor_chain()
is used:
https://github.com/rust-vmm/vm-virtio/blob/863837ef863f6880bb8357e60bbac49e72c0844c/virtio-queue/src/queue.rs#L583
A reasonable approach, implemented here, is to mark the device as
NEEDS_RESET and ignore further queue events until the guest
reinitializes the device.
How this patch was tested:
Linux kernel was patched to trigger a bad next_avail when the
virtqueue queue counter reaches 5000:
--------------- START OF LINUX KERNEL PATCH ----------
$ git diff
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index b784aab668670..989f2a0c64a77 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -15,6 +15,9 @@
#include <linux/spinlock.h>
#include <xen/xen.h>
+
+void virtqueue_kick_always(struct virtqueue *vq);
+
#ifdef DEBUG
/* For development, we want to crash whenever the ring is screwed. */
#define BAD_RING(_vq, fmt, args...) \
@@ -677,6 +680,12 @@ static inline int virtqueue_add_split(
struct virtqueue *_vq,
* new available array entries. */
virtio_wmb(vq->weak_barriers);
vq->split.avail_idx_shadow++;
+ {
+ if ((vq->split.avail_idx_shadow % 100) == 0)
+ printk(KERN_ERR "avail idx: %d",
+ (int)vq->split.avail_idx_shadow);
+ if (vq->split.avail_idx_shadow == 5000)
+ vq->split.avail_idx_shadow = 0;
+ }
vq->split.vring.avail->idx = cpu_to_virtio16(_vq->vdev,
vq->split.avail_idx_shadow);
vq->num_added++;
@@ -689,6 +698,11 @@ static inline int virtqueue_add_split(
struct virtqueue *_vq,
if (unlikely(vq->num_added == (1 << 16) - 1))
virtqueue_kick(_vq);
+ {
+ if (unlikely(vq->split.avail_idx_shadow == 0))
+ virtqueue_kick_always(_vq);
+ }
+
return 0;
unmap_release:
@@ -2515,6 +2529,11 @@ bool virtqueue_kick(struct virtqueue *vq)
}
EXPORT_SYMBOL_GPL(virtqueue_kick);
+void virtqueue_kick_always(struct virtqueue *vq)
+{
+ virtqueue_kick_prepare(vq);
+ virtqueue_notify(vq);
+}
/**
* virtqueue_get_buf_ctx - get the next used buffer
* @_vq: the struct virtqueue we're talking about.
--------------- END OF LINUX KERNEL PATCH ----------
Then the kernel was booted, and the host pinged until the
nic became unresponsive:
ping -i 0.002 192.168.4.1
Device status was confirmed using
cat /sys/class/net/eth0/device/status
(it was 0x4f).
Then the device was re-initialized:
DEV_NAME=$(basename $(readlink -f /sys/class/net/eth0/device))
echo $DEV_NAME | tee /sys/bus/virtio/drivers/virtio_net/unbind
echo $DEV_NAME | tee /sys/bus/virtio/drivers/virtio_net/bind
ip link set eth0 up
At this point networking became healthly again.
Signed-off-by: Peter Oskolkov <posk@google.com>
(cherry picked from commit 563303b50a)