lkdtm: Add Control Flow Integrity test

This adds a simple test for forward CFI (indirect function calls) with
function prototype granularity (as implemented by Clang's CFI).

Signed-off-by: Kees Cook <keescook@chromium.org>

1 files changed, 42 insertions, 0 deletions

diff --git a/drivers/misc/lkdtm/cfi.c b/drivers/misc/lkdtm/cfi.c
new file mode 100644
index 000000000000..e73ebdbfa806
--- /dev/null
+++ b/drivers/misc/lkdtm/cfi.c
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This is for all the tests relating directly to Control Flow Integrity.
+ */
+#include "lkdtm.h"
+
+static int called_count;
+
+/* Function taking one argument, without a return value. */
+static noinline void lkdtm_increment_void(int *counter)
+{
+	(*counter)++;
+}
+
+/* Function taking one argument, returning int. */
+static noinline int lkdtm_increment_int(int *counter)
+{
+	(*counter)++;
+
+	return *counter;
+}
+/*
+ * This tries to call an indirect function with a mismatched prototype.
+ */
+void lkdtm_CFI_FORWARD_PROTO(void)
+{
+	/*
+	 * Matches lkdtm_increment_void()'s prototype, but not
+	 * lkdtm_increment_int()'s prototype.
+	 */
+	void (*func)(int *);
+
+	pr_info("Calling matched prototype ...\n");
+	func = lkdtm_increment_void;
+	func(&called_count);
+
+	pr_info("Calling mismatched prototype ...\n");
+	func = (void *)lkdtm_increment_int;
+	func(&called_count);
+
+	pr_info("Fail: survived mismatched prototype function call!\n");
+}