1 files changed, 9 insertions, 2 deletions

diff --git a/drivers/s390/kvm/virtio_ccw.c b/drivers/s390/kvm/virtio_ccw.c
index 6f1fa1773e76..f8d8fdb26b72 100644
--- a/drivers/s390/kvm/virtio_ccw.c
+++ b/drivers/s390/kvm/virtio_ccw.c
@@ -65,6 +65,7 @@ struct virtio_ccw_device {
         bool is_thinint;
         bool going_away;
         bool device_lost;
+        unsigned int config_ready;
         void *airq_info;
 };
 
@@ -833,8 +834,11 @@ static void virtio_ccw_get_config(struct virtio_device *vdev,
         if (ret)
                 goto out_free;
 
-        memcpy(vcdev->config, config_area, sizeof(vcdev->config));
-        memcpy(buf, &vcdev->config[offset], len);
+        memcpy(vcdev->config, config_area, offset + len);
+        if (buf)
+                memcpy(buf, &vcdev->config[offset], len);
+        if (vcdev->config_ready < offset + len)
+                vcdev->config_ready = offset + len;
 
 out_free:
         kfree(config_area);
@@ -857,6 +861,9 @@ static void virtio_ccw_set_config(struct virtio_device *vdev,
         if (!config_area)
                 goto out_free;
 
+        /* Make sure we don't overwrite fields. */
+        if (vcdev->config_ready < offset)
+                virtio_ccw_get_config(vdev, 0, NULL, offset);
         memcpy(&vcdev->config[offset], buf, len);
         /* Write the config area to the host. */
         memcpy(config_area, vcdev->config, sizeof(vcdev->config));