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

[Kees Cook]

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@xxxxxxxxxxxx>
---
 kernel/Makefile      |    1 +
 kernel/test_module.c |   26 ++++++++++++++++++++++++++
 lib/Kconfig.debug    |   14 ++++++++++++++
 3 files changed, 41 insertions(+)
 create mode 100644 kernel/test_module.c

diff --git a/kernel/Makefile b/kernel/Makefile
index bbaf7d59c1bb..9de0f0e89937 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -59,6 +59,7 @@ obj-$(CONFIG_IKCONFIG) += configs.o
 obj-$(CONFIG_RESOURCE_COUNTERS) += res_counter.o
 obj-$(CONFIG_SMP) += stop_machine.o
 obj-$(CONFIG_KPROBES_SANITY_TEST) += test_kprobes.o
+obj-$(CONFIG_TEST_MODULE) += test_module.o
 obj-$(CONFIG_AUDIT) += audit.o auditfilter.o
 obj-$(CONFIG_AUDITSYSCALL) += auditsc.o
 obj-$(CONFIG_AUDIT_WATCH) += audit_watch.o
diff --git a/kernel/test_module.c b/kernel/test_module.c
new file mode 100644
index 000000000000..f825589315d7
--- /dev/null
+++ b/kernel/test_module.c
@@ -0,0 +1,26 @@
+/*
+ * "hello world" kernel module
+ */
+
+#define pr_fmt(fmt) "test_module: " fmt
+
+#include <linux/module.h>
+
+static int __init test_module_init(void)
+{
+	pr_info("Hello, world\n");
+
+	return 0;
+}
+
+module_init(test_module_init);
+
+static void __exit test_module_exit(void)
+{
+	pr_info("Goodbye\n");
+}
+
+module_exit(test_module_exit);
+
+MODULE_AUTHOR("Kees Cook <keescook@xxxxxxxxxxxx>");
+MODULE_LICENSE("GPL");
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index db25707aa41b..20abc92032e0 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
+	  request by name.
+
+	  If unsure, say N.
+
 source "samples/Kconfig"
 
 source "lib/Kconfig.kgdb"
-- 
1.7.9.5

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