fortify: Add KUnit test for FORTIFY_SOURCE internals

Add lib/fortify_kunit.c KUnit test for checking the expected behavioral
characteristics of FORTIFY_SOURCE internals.

Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Tom Rix <trix@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: "Steven Rostedt (Google)" <rostedt@goodmis.org>
Cc: Yury Norov <yury.norov@gmail.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Sander Vanheule <sander@svanheule.net>
Cc: linux-hardening@vger.kernel.org
Cc: llvm@lists.linux.dev
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

1 files changed, 77 insertions, 0 deletions

diff --git a/lib/fortify_kunit.c b/lib/fortify_kunit.c
new file mode 100644
index 000000000000..99bc0ea60d27
--- /dev/null
+++ b/lib/fortify_kunit.c
@@ -0,0 +1,77 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Runtime test cases for CONFIG_FORTIFY_SOURCE that aren't expected to
+ * Oops the kernel on success. (For those, see drivers/misc/lkdtm/fortify.c)
+ *
+ * For corner cases with UBSAN, try testing with:
+ *
+ * ./tools/testing/kunit/kunit.py run --arch=x86_64 \
+ *	--kconfig_add CONFIG_FORTIFY_SOURCE=y \
+ *	--kconfig_add CONFIG_UBSAN=y \
+ *	--kconfig_add CONFIG_UBSAN_TRAP=y \
+ *	--kconfig_add CONFIG_UBSAN_BOUNDS=y \
+ *	--kconfig_add CONFIG_UBSAN_LOCAL_BOUNDS=y \
+ *	--make_options LLVM=1 fortify
+ */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <kunit/test.h>
+#include <linux/string.h>
+#include <linux/init.h>
+
+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";
+
+static void known_sizes_test(struct kunit *test)
+{
+	KUNIT_EXPECT_EQ(test, __compiletime_strlen("88888888"), 8);
+	KUNIT_EXPECT_EQ(test, __compiletime_strlen(array_of_10), 10);
+	KUNIT_EXPECT_EQ(test, __compiletime_strlen(ptr_of_11), 11);
+
+	KUNIT_EXPECT_EQ(test, __compiletime_strlen(array_unknown), SIZE_MAX);
+	/* Externally defined and dynamically sized string pointer: */
+	KUNIT_EXPECT_EQ(test, __compiletime_strlen(saved_command_line), SIZE_MAX);
+}
+
+/* This is volatile so the optimizer can't perform DCE below. */
+static volatile int pick;
+
+/* Not inline to keep optimizer from figuring out which string we want. */
+static noinline size_t want_minus_one(int pick)
+{
+	const char *str;
+
+	switch (pick) {
+	case 1:
+		str = "4444";
+		break;
+	case 2:
+		str = "333";
+		break;
+	default:
+		str = "1";
+		break;
+	}
+	return __compiletime_strlen(str);
+}
+
+static void control_flow_split_test(struct kunit *test)
+{
+	KUNIT_EXPECT_EQ(test, want_minus_one(pick), SIZE_MAX);
+}
+
+static struct kunit_case fortify_test_cases[] = {
+	KUNIT_CASE(known_sizes_test),
+	KUNIT_CASE(control_flow_split_test),
+	{}
+};
+
+static struct kunit_suite fortify_test_suite = {
+	.name = "fortify",
+	.test_cases = fortify_test_cases,
+};
+
+kunit_test_suite(fortify_test_suite);
+
+MODULE_LICENSE("GPL");