[PATCH RFC v5 12/19] virtio: disallow late feature changes for virtio-1

[Cornelia Huck <cornelia.huck@xxxxxxxxxx>]

For virtio-1 devices, the driver must not attempt to set feature bits
after it set FEATURES_OK in the device status. Simply reject it in
that case.

Signed-off-by: Cornelia Huck <cornelia.huck@xxxxxxxxxx>
---
 hw/virtio/virtio.c         |   16 ++++++++++++++--
 include/hw/virtio/virtio.h |    2 ++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 508dccf..4f2dc48 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -980,7 +980,7 @@ void virtio_save(VirtIODevice *vdev, QEMUFile *f)
     vmstate_save_state(f, &vmstate_virtio, vdev);
 }
 
-int virtio_set_features(VirtIODevice *vdev, uint64_t val)
+static int __virtio_set_features(VirtIODevice *vdev, uint64_t val)
 {
     BusState *qbus = qdev_get_parent_bus(DEVICE(vdev));
     VirtioBusClass *vbusk = VIRTIO_BUS_GET_CLASS(qbus);
@@ -996,6 +996,18 @@ int virtio_set_features(VirtIODevice *vdev, uint64_t val)
     return bad ? -1 : 0;
 }
 
+int virtio_set_features(VirtIODevice *vdev, uint64_t val)
+{
+   /*
+     * The driver must not attempt to set features after feature negotiation
+     * has finished.
+     */
+    if (vdev->status & VIRTIO_CONFIG_S_FEATURES_OK) {
+        return -EINVAL;
+    }
+    return __virtio_set_features(vdev, val);
+}
+
 int virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id)
 {
     int i, ret;
@@ -1028,7 +1040,7 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id)
     qemu_get_be32s(f, &features);
 
     /* XXX features >= 32 */
-    if (virtio_set_features(vdev, features) < 0) {
+    if (__virtio_set_features(vdev, features) < 0) {
         supported_features = k->get_features(qbus->parent);
         error_report("Features 0x%x unsupported. Allowed features: 0x%lx",
                      features, supported_features);
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 80ee313..9a984c2 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -32,6 +32,8 @@
 #define VIRTIO_CONFIG_S_DRIVER          2
 /* Driver has used its parts of the config, and is happy */
 #define VIRTIO_CONFIG_S_DRIVER_OK       4
+/* Driver has finished configuring features */
+#define VIRTIO_CONFIG_S_FEATURES_OK     8
 /* We've given up on this device. */
 #define VIRTIO_CONFIG_S_FAILED          0x80
 
-- 
1.7.9.5

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