userspace: easy checking for specific driver

doc/kernel/usermode/syscalls.rst

@@ -299,6 +299,14 @@ Several macros exist to validate arguments:
   instance, to validate the GPIO driver, one could use the
   :c:macro:`Z_SYSCALL_DRIVER_GPIO()` macro.
 
+* :c:macro:`Z_SYSCALL_SPECIFIC_DRIVER()` is a runtime check to verify that
+  a provided pointer is a valid instance of a specific device driver, that
+  the calling thread has permissions on it, and that the driver has been
+  initialized. It does this by checking the init function pointer that
+  is stored within the driver instance and ensuring that it matches the
+  provided value, which should be the address of the specific driver's
+  init function.
+
 If any check fails, the macros will return a nonzero value. The macro
 :c:macro:`Z_OOPS()` can be used to induce a kernel oops which will kill the
 calling thread. This is done instead of returning some error condition to

kernel/include/syscall_handler.h

@@ -434,6 +434,33 @@ static inline int _obj_validation_check(struct _k_object *ko,
 				    # op, __device__); \
 	})
 
+/**
+ * @brief Runtime check that device object is of a specific driver type
+ *
+ * Checks that the driver object passed in is initialized, the caller has
+ * correct permissions, and that it belongs to the specified driver
+ * subsystems. Additionally, all devices store a function pointer to the
+ * driver's init function. If this doesn't match the value provided, the
+ * check will fail.
+ *
+ * This provides an easy way to determine if a device object not only
+ * belongs to a particular subsystem, but is of a specific device driver
+ * implementation. Useful for defining out-of-subsystem system calls
+ * which are implemented for only one driver.
+ *
+ * @param _device Untrusted device pointer
+ * @param _dtype Expected kernel object type for the provided device pointer
+ * @param _init_fn Expected init function memory address
+ * @return 0 on success, nonzero on failure
+ */
+#define Z_SYSCALL_SPECIFIC_DRIVER(_device, _dtype, _init_fn) \
+	({ \
+		struct device *_dev = (struct device *)_device; \
+		Z_SYSCALL_OBJ(_dev, _dtype) || \
+			Z_SYSCALL_VERIFY_MSG(_dev->config->init == _init_fn, \
+					     "init function mismatch"); \
+	})
+
 /**
  * @brief Runtime check kernel object pointer for non-init functions
  *