[Qemu-devel] [PATCH RFC] vhost: ring: verify ring is not being moved

[Michael S. Tsirkin]

abort if it is

Signed-off-by: Michael S. Tsirkin <address@hidden>
---

So the following is a simple solution for unstable
ring mappings security issue: simply detect this and stop.

Will repost series with this later after some testing,
but this is an RFC to get early feedback if any.

 hw/vhost.c |   52 +++++++++++++++++++++++++++++++++++++++++++++++++---
 hw/vhost.h |    3 +++
 2 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/hw/vhost.c b/hw/vhost.c
index 3b3a109..b9e115e 100644
--- a/hw/vhost.c
+++ b/hw/vhost.c
@@ -256,6 +256,33 @@ static inline void vhost_dev_log_resize(struct vhost_dev* 
dev, uint64_t size)
     dev->log_size = size;
 }
 
+static int vhost_verify_ring_mappings(struct vhost_dev *dev,
+                                      uint64_t start_addr,
+                                      uint64_t size)
+{
+    int i;
+    for (i = 0; i < dev->nvqs; ++i) {
+        struct vhost_virtqueue *vq = dev->vqs + i;
+        target_phys_addr_t l;
+        void *p;
+
+        if (!ranges_overlap(start_addr, size, vq->ring_phys, vq->ring_size))
+            continue;
+        l = vq->ring_size;
+        p = cpu_physical_memory_map(vq->ring_phys, &l, 1);
+        if (!p || l != vq->ring_size) {
+            fprintf(stderr, "Unable to map ring buffer for ring %d\n", i);
+            return -ENOMEM;
+        }
+        if (p != vq->ring) {
+            fprintf(stderr, "Ring buffer relocated for ring %d\n", i);
+            return -EBUSY;
+        }
+        cpu_physical_memory_unmap(p, l, 0, 0);
+    }
+    return 0;
+}
+
 static void vhost_client_set_memory(CPUPhysMemoryClient *client,
                                     target_phys_addr_t start_addr,
                                     ram_addr_t size,
@@ -284,6 +311,12 @@ static void vhost_client_set_memory(CPUPhysMemoryClient 
*client,
     if (!dev->started) {
         return;
     }
+
+    if (dev->started) {
+        r = vhost_verify_ring_mappings(dev, start_addr, size);
+        assert(r >= 0);
+    }
+
     if (!dev->log_enabled) {
         r = ioctl(dev->control, VHOST_SET_MEM_TABLE, dev->mem);
         assert(r >= 0);
@@ -442,6 +475,14 @@ static int vhost_virtqueue_init(struct vhost_dev *dev,
         goto fail_alloc_used;
     }
 
+    vq->ring_size = s = l = virtio_queue_get_ring_size(vdev, idx);
+    vq->ring_phys = a = virtio_queue_get_ring(vdev, idx);
+    vq->ring = cpu_physical_memory_map(a, &l, 1);
+    if (!vq->ring || l != s) {
+        r = -ENOMEM;
+        goto fail_alloc_ring;
+    }
+
     r = vhost_virtqueue_set_addr(dev, vq, idx, dev->log_enabled);
     if (r < 0) {
         r = -errno;
@@ -485,6 +526,9 @@ fail_host_notifier:
     vdev->binding->guest_notifier(vdev->binding_opaque, idx, false);
 fail_guest_notifier:
 fail_alloc:
+    cpu_physical_memory_unmap(vq->ring, virtio_queue_get_ring_size(vdev, idx),
+                              0, 0);
+fail_alloc_ring:
     cpu_physical_memory_unmap(vq->used, virtio_queue_get_used_size(vdev, idx),
                               0, 0);
 fail_alloc_used:
@@ -526,12 +570,14 @@ static void vhost_virtqueue_cleanup(struct vhost_dev *dev,
     }
     virtio_queue_set_last_avail_idx(vdev, idx, state.num);
     assert (r >= 0);
+    cpu_physical_memory_unmap(vq->ring, virtio_queue_get_ring_size(vdev, idx),
+                              0, virtio_queue_get_ring_size(vdev, idx));
     cpu_physical_memory_unmap(vq->used, virtio_queue_get_used_size(vdev, idx),
                               0, 0);
     cpu_physical_memory_unmap(vq->avail, virtio_queue_get_avail_size(vdev, 
idx),
                               0, 0);
     cpu_physical_memory_unmap(vq->desc, virtio_queue_get_desc_size(vdev, idx),
                               0, 0);
 }
 
 int vhost_dev_init(struct vhost_dev *hdev, int devfd)
diff --git a/hw/vhost.h b/hw/vhost.h
index 48b52c7..86dd834 100644
--- a/hw/vhost.h
+++ b/hw/vhost.h
@@ -14,6 +14,9 @@ struct vhost_virtqueue {
     int num;
     unsigned long long used_phys;
     unsigned used_size;
+    void *ring;
+    unsigned long long ring_phys;
+    unsigned ring_size;
 };
 
 typedef unsigned long vhost_log_chunk_t;
-- 
1.7.0.18.g0d53a5