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>

diff --git a/Documentation/dev-tools/kunit/usage.rst b/Documentation/dev-tools/kunit/usage.rst
index c27e1646ecd9caf60faeda70a0d2be1a0d395d00..9db12e91668e30647b72081c5d1fdd019d67d478 100644 (file)
--- a/Documentation/dev-tools/kunit/usage.rst
+++ b/Documentation/dev-tools/kunit/usage.rst
@@ -651,12 +651,16 @@ For example:
        }
 
 Note that, for functions like device_unregister which only accept a single
-pointer-sized argument, it's possible to directly cast that function to
-a ``kunit_action_t`` rather than writing a wrapper function, for example:
+pointer-sized argument, it's possible to automatically generate a wrapper
+with the ``KUNIT_DEFINE_ACTION_WRAPPER()`` macro, for example:
 
 .. code-block:: C
 
-       kunit_add_action(test, (kunit_action_t *)&device_unregister, &dev);
+       KUNIT_DEFINE_ACTION_WRAPPER(device_unregister, device_unregister_wrapper, struct device *);
+       kunit_add_action(test, &device_unregister_wrapper, &dev);
+
+You should do this in preference to manually casting to the ``kunit_action_t`` type,
+as casting function pointers will break Control Flow Integrity (CFI).
 
 ``kunit_add_action`` can fail if, for example, the system is out of memory.
 You can use ``kunit_add_action_or_reset`` instead which runs the action

diff --git a/include/kunit/resource.h b/include/kunit/resource.h
index c7383e90f5c9e7e6d59c2aca916a509a27d36e10..4ad69a2642a51cffc3b000f6057f28016a6f3fc3 100644 (file)
--- a/include/kunit/resource.h
+++ b/include/kunit/resource.h
@@ -390,6 +390,27 @@ void kunit_remove_resource(struct kunit *test, struct kunit_resource *res);
 /* A 'deferred action' function to be used with kunit_add_action. */
 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.

diff --git a/lib/kunit/kunit-test.c b/lib/kunit/kunit-test.c
index de2113a58fa034f4da20e4ee2b9734c3092b1017..ee6927c609797201b4262681c476a0ea50b26b9d 100644 (file)
--- a/lib/kunit/kunit-test.c
+++ b/lib/kunit/kunit-test.c
@@ -538,10 +538,7 @@ static struct kunit_suite kunit_resource_test_suite = {
 #if IS_BUILTIN(CONFIG_KUNIT_TEST)
 
 /* This avoids a cast warning if kfree() is passed direct to kunit_add_action(). */
-static void kfree_wrapper(void *p)
-{
-       kfree(p);
-}
+KUNIT_DEFINE_ACTION_WRAPPER(kfree_wrapper, kfree, const void *);
 
 static void kunit_log_test(struct kunit *test)
 {

diff --git a/lib/kunit/test.c b/lib/kunit/test.c
index 7aceb07a1af9f64ab619cf7bb9a061e1b3276962..7deee3701d206f0ff254342702344f0071c56c32 100644 (file)
--- a/lib/kunit/test.c
+++ b/lib/kunit/test.c
@@ -810,6 +810,8 @@ static struct notifier_block kunit_mod_nb = {
 };
 #endif
 
+KUNIT_DEFINE_ACTION_WRAPPER(kfree_action_wrapper, kfree, const void *)
+
 void *kunit_kmalloc_array(struct kunit *test, size_t n, size_t size, gfp_t gfp)
 {
        void *data;
@@ -819,7 +821,7 @@ void *kunit_kmalloc_array(struct kunit *test, size_t n, size_t size, gfp_t gfp)
        if (!data)
                return NULL;
 
-       if (kunit_add_action_or_reset(test, (kunit_action_t *)kfree, data) != 0)
+       if (kunit_add_action_or_reset(test, kfree_action_wrapper, data) != 0)
                return NULL;
 
        return data;
@@ -831,7 +833,7 @@ void kunit_kfree(struct kunit *test, const void *ptr)
        if (!ptr)
                return;
 
-       kunit_release_action(test, (kunit_action_t *)kfree, (void *)ptr);
+       kunit_release_action(test, kfree_action_wrapper, (void *)ptr);
 }
 EXPORT_SYMBOL_GPL(kunit_kfree);