[PATCH v3 1/2] test: add minimal module for verification testing

[Kees Cook <keescook@chromium.org>]

When doing module loading verification tests (for example, with module
singing, or LSM hooks), it is very handy to have a module that can be
built on all systems under test, isn't auto-loaded at boot, and has
no device or similar dependencies. This creates the "test_module.ko"
module for that purpose, which only reports its load and unload to printk.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
v3:
 - use KBUILD_MODNAME; Rusty Russell
v2:
 - use pr_warn, better comment, add headers explicitly, move to lib/; akpm.
---
 lib/Kconfig.debug |   14 ++++++++++++++
 lib/Makefile      |    1 +
 lib/test_module.c |   33 +++++++++++++++++++++++++++++++++
 3 files changed, 48 insertions(+)
 create mode 100644 lib/test_module.c

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index db25707aa41b..81882335c625 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1578,6 +1578,20 @@ config DMA_API_DEBUG
 	  This option causes a performance degredation.  Use only if you want
 	  to debug device drivers. If unsure, say N.
 
+config TEST_MODULE
+	tristate "Test module loading with 'hello world' module"
+	default n
+	depends on m
+	help
+	  This builds the "test_module" module that emits "Hello, world"
+	  on printk when loaded. It is designed to be used for basic
+	  evaluation of the module loading subsystem (for example when
+	  validating module verification). It lacks any extra dependencies,
+	  and will not normally be loaded by the system unless explicitly
+	  requested by name.
+
+	  If unsure, say N.
+
 source "samples/Kconfig"
 
 source "lib/Kconfig.kgdb"
diff --git a/lib/Makefile b/lib/Makefile
index a459c31e8c6b..b494b9af631c 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -31,6 +31,7 @@ obj-y += string_helpers.o
 obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
 obj-y += kstrtox.o
 obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
+obj-$(CONFIG_TEST_MODULE) += test_module.o
 
 ifeq ($(CONFIG_DEBUG_KOBJECT),y)
 CFLAGS_kobject.o += -DDEBUG
diff --git a/lib/test_module.c b/lib/test_module.c
new file mode 100644
index 000000000000..319b66f1ff61
--- /dev/null
+++ b/lib/test_module.c
@@ -0,0 +1,33 @@
+/*
+ * This module emits "Hello, world" on printk when loaded.
+ *
+ * It is designed to be used for basic evaluation of the module loading
+ * subsystem (for example when validating module signing/verification). It
+ * lacks any extra dependencies, and will not normally be loaded by the
+ * system unless explicitly requested by name.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+
+static int __init test_module_init(void)
+{
+	pr_warn("Hello, world\n");
+
+	return 0;
+}
+
+module_init(test_module_init);
+
+static void __exit test_module_exit(void)
+{
+	pr_warn("Goodbye\n");
+}
+
+module_exit(test_module_exit);
+
+MODULE_AUTHOR("Kees Cook <keescook@chromium.org>");
+MODULE_LICENSE("GPL");
-- 
1.7.9.5