android: Enable building ashmem and binder as modules

We want to enable use of the Android ashmem and binder drivers to
support Anbox, but they should not be built-in as that would waste
resources and increase security attack surface on systems that don't
need them.

- Add a MODULE_LICENSE declaration to ashmem
- Change the Makefiles to build each driver as an object with the
  "_linux" suffix (which is what Anbox expects)
- Change config symbol types to tristate

drivers/android/Kconfig

@@ -9,7 +9,7 @@ config ANDROID
 if ANDROID
 
 config ANDROID_BINDER_IPC
-	bool "Android Binder IPC Driver"
+	tristate "Android Binder IPC Driver"
 	depends on MMU
 	default n
 	help

drivers/android/Makefile

@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 ccflags-y += -I$(src)			# needed for trace events
 
-obj-$(CONFIG_ANDROID_BINDERFS)		+= binderfs.o
-obj-$(CONFIG_ANDROID_BINDER_IPC)	+= binder.o binder_alloc.o
-obj-$(CONFIG_ANDROID_BINDER_IPC_SELFTEST) += binder_alloc_selftest.o
+obj-$(CONFIG_ANDROID_BINDER_IPC)	+= binder_linux.o
+binder_linux-y := binder.o binder_alloc.o
+binder_linux-$(CONFIG_ANDROID_BINDERFS)	+= binderfs.o
+binder_linux-$(CONFIG_ANDROID_BINDER_IPC_SELFTEST) += binder_alloc_selftest.o

drivers/android/binder_alloc.c

@@ -38,7 +38,7 @@ enum {
 };
 static uint32_t binder_alloc_debug_mask = BINDER_DEBUG_USER_ERROR;
 
-module_param_named(debug_mask, binder_alloc_debug_mask,
+module_param_named(alloc_debug_mask, binder_alloc_debug_mask,
 		   uint, 0644);
 
 #define binder_alloc_debug(mask, x...) \

drivers/staging/android/Kconfig

@@ -4,7 +4,7 @@ menu "Android"
 if ANDROID
 
 config ASHMEM
-	bool "Enable the Anonymous Shared Memory Subsystem"
+	tristate "Enable the Anonymous Shared Memory Subsystem"
 	depends on SHMEM
 	help
 	  The ashmem subsystem is a new shared memory allocator, similar to

drivers/staging/android/Makefile

@@ -3,4 +3,5 @@ ccflags-y += -I$(src)			# needed for trace events
 
 obj-y					+= ion/
 
-obj-$(CONFIG_ASHMEM)			+= ashmem.o
+obj-$(CONFIG_ASHMEM)			+= ashmem_linux.o
+ashmem_linux-y				+= ashmem.o

drivers/staging/android/ashmem.c

@@ -24,6 +24,7 @@
 #include <linux/bitops.h>
 #include <linux/mutex.h>
 #include <linux/shmem_fs.h>
+#include <linux/module.h>
 #include "ashmem.h"
 
 #define ASHMEM_NAME_PREFIX "dev/ashmem/"
@@ -965,3 +966,5 @@ static int __init ashmem_init(void)
 	return ret;
 }
 device_initcall(ashmem_init);
+
+MODULE_LICENSE("GPL v2");