fortify: Allow KUnit test to build without FORTIFY

In order for CI systems to notice all the skipped tests related to
CONFIG_FORTIFY_SOURCE, allow the FORTIFY_SOURCE KUnit tests to build
with or without CONFIG_FORTIFY_SOURCE.
Signed-off-by: Kees Cook <keescook@chromium.org>

lib/Kconfig.debug

@@ -2645,7 +2645,7 @@ config STACKINIT_KUNIT_TEST
 
 config FORTIFY_KUNIT_TEST
 	tristate "Test fortified str*() and mem*() function internals at runtime" if !KUNIT_ALL_TESTS
-	depends on KUNIT && FORTIFY_SOURCE
+	depends on KUNIT
 	default KUNIT_ALL_TESTS
 	help
 	  Builds unit tests for checking internals of FORTIFY_SOURCE as used

lib/fortify_kunit.c

@@ -25,6 +25,11 @@ static const char array_of_10[] = "this is 10";
 static const char *ptr_of_11 = "this is 11!";
 static char array_unknown[] = "compiler thinks I might change";
 
+/* Handle being built without CONFIG_FORTIFY_SOURCE */
+#ifndef __compiletime_strlen
+# define __compiletime_strlen __builtin_strlen
+#endif
+
 static void known_sizes_test(struct kunit *test)
 {
 	KUNIT_EXPECT_EQ(test, __compiletime_strlen("88888888"), 8);
@@ -307,6 +312,14 @@ DEFINE_ALLOC_SIZE_TEST_PAIR(kvmalloc)
 } while (0)
 DEFINE_ALLOC_SIZE_TEST_PAIR(devm_kmalloc)
 
+static int fortify_test_init(struct kunit *test)
+{
+	if (!IS_ENABLED(CONFIG_FORTIFY_SOURCE))
+		kunit_skip(test, "Not built with CONFIG_FORTIFY_SOURCE=y");
+
+	return 0;
+}
+
 static struct kunit_case fortify_test_cases[] = {
 	KUNIT_CASE(known_sizes_test),
 	KUNIT_CASE(control_flow_split_test),
@@ -323,6 +336,7 @@ static struct kunit_case fortify_test_cases[] = {
 
 static struct kunit_suite fortify_test_suite = {
 	.name = "fortify",
+	.init = fortify_test_init,
 	.test_cases = fortify_test_cases,
 };