um: virtio_uml: Disallow modular build

This driver *can* be a module, but then its parameters (socket path)
are untrusted data from inside the VM, and that isn't allowed. Allow
the code to only be built-in to avoid that.

Fixes: 5d38f324 ("um: drivers: Add virtio vhost-user driver")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-by: Anton Ivanov <anton.ivanov@cambridgegreys.co.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/drivers/Kconfig

@@ -337,7 +337,7 @@ config UML_NET_SLIRP
 endmenu
 
 config VIRTIO_UML
-	tristate "UML driver for virtio devices"
+	bool "UML driver for virtio devices"
 	select VIRTIO
 	help
 	  This driver provides support for virtio based paravirtual device

arch/um/drivers/virtio_uml.c

@@ -4,12 +4,12 @@
  *
  * Copyright(c) 2019 Intel Corporation
  *
- * This module allows virtio devices to be used over a vhost-user socket.
+ * This driver allows virtio devices to be used over a vhost-user socket.
  *
  * Guest devices can be instantiated by kernel module or command line
  * parameters. One device will be created for each parameter. Syntax:
  *
- *		[virtio_uml.]device=<socket>:<virtio_id>[:<platform_id>]
+ *		virtio_uml.device=<socket>:<virtio_id>[:<platform_id>]
  * where:
  *		<socket>	:= vhost-user socket path to connect
  *		<virtio_id>	:= virtio device id (as in virtio_ids.h)