kunit: Add a macro to wrap a deferred action function

KUnit's deferred action API accepts a void(*)(void *) function pointer
which is called when the test is exited. However, we very frequently
want to use existing functions which accept a single pointer, but which
may not be of type void*. While this is probably dodgy enough to be on
the wrong side of the C standard, it's been often used for similar
callbacks, and gcc's -Wcast-function-type seems to ignore cases where
the only difference is the type of the argument, assuming it's
compatible (i.e., they're both pointers to data).

However, clang 16 has introduced -Wcast-function-type-strict, which no
longer permits any deviation in function pointer type. This seems to be
because it'd break CFI, which validates the type of function calls.

This rather ruins our attempts to cast functions to defer them, and
leaves us with a few options. The one we've chosen is to implement a
macro which will generate a wrapper function which accepts a void*, and
casts the argument to the appropriate type.

For example, if you were trying to wrap:
void foo_close(struct foo *handle);
you could use:
KUNIT_DEFINE_ACTION_WRAPPER(kunit_action_foo_close,
			    foo_close,
			    struct foo *);

This would create a new kunit_action_foo_close() function, of type
kunit_action_t, which could be passed into kunit_add_action() and
similar functions.

In addition to defining this macro, update KUnit and its tests to use
it.

Link: https://github.com/ClangBuiltLinux/linux/issues/1750
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Daniel Vetter <daniel@ffwll.ch>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

1 files changed, 21 insertions, 0 deletions

diff --git a/include/kunit/resource.h b/include/kunit/resource.h
index c7383e90f5c9..4ad69a2642a5 100644
--- a/include/kunit/resource.h
+++ b/include/kunit/resource.h
@@ -391,6 +391,27 @@ void kunit_remove_resource(struct kunit *test, struct kunit_resource *res);
 typedef void (kunit_action_t)(void *);
 
 /**
+ * KUNIT_DEFINE_ACTION_WRAPPER() - Wrap a function for use as a deferred action.
+ *
+ * @wrapper: The name of the new wrapper function define.
+ * @orig: The original function to wrap.
+ * @arg_type: The type of the argument accepted by @orig.
+ *
+ * Defines a wrapper for a function which accepts a single, pointer-sized
+ * argument. This wrapper can then be passed to kunit_add_action() and
+ * similar. This should be used in preference to casting a function
+ * directly to kunit_action_t, as casting function pointers will break
+ * control flow integrity (CFI), leading to crashes.
+ */
+#define KUNIT_DEFINE_ACTION_WRAPPER(wrapper, orig, arg_type)	\
+	static void wrapper(void *in)				\
+	{							\
+		arg_type arg = (arg_type)in;			\
+		orig(arg);					\
+	}
+
+
+/**
  * kunit_add_action() - Call a function when the test ends.
  * @test: Test case to associate the action with.
  * @action: The function to run on test exit