lkdtm: clean up sparse warnings

Since lkdtm intentionally does "bad" things, we need to convince sparse
that we're doing these things on purpose. This adds an explicit cast
to the call to copy_to_user() and marks the spin lock as expecting
to dead-lock.
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/lkdtm.c

@@ -334,9 +334,10 @@ static void execute_location(void *dst)
 
 static void execute_user_location(void *dst)
 {
+	/* Intentionally crossing kernel/user memory boundary. */
 	void (*func)(void) = dst;
 
-	if (copy_to_user(dst, do_nothing, EXEC_SIZE))
+	if (copy_to_user((void __user *)dst, do_nothing, EXEC_SIZE))
 		return;
 	func();
 }
@@ -408,6 +409,8 @@ static void lkdtm_do_action(enum ctype which)
 	case CT_SPINLOCKUP:
 		/* Must be called twice to trigger. */
 		spin_lock(&lock_me_up);
+		/* Let sparse know we intended to exit holding the lock. */
+		__release(&lock_me_up);
 		break;
 	case CT_HUNG_TASK:
 		set_current_state(TASK_UNINTERRUPTIBLE);