lkdtm: fix stack protector trigger

The -fstack-protector compiler flag will only build stack protections if
a character array is seen. Additionally, the offset to the saved
instruction pointer changes based on architecture, so stomp much harder
(64 bytes) when corrupting the stack.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/lkdtm.c

@@ -295,10 +295,10 @@ static void lkdtm_do_action(enum ctype which)
 		(void) recursive_loop(0);
 		break;
 	case CT_CORRUPT_STACK: {
-		volatile u32 data[8];
-		volatile u32 *p = data;
+		/* Make sure the compiler creates and uses an 8 char array. */
+		volatile char data[8];
 
-		p[12] = 0x12345678;
+		memset((void *)data, 0, 64);
 		break;
 	}
 	case CT_UNALIGNED_LOAD_STORE_WRITE: {