Secure OS extensibility needn't cost an arm and a leg

This paper makes the claim that secure extensibility of operating systems is not only desirable but also achievable. We claim that OS extensibility should be done at user-level to avoid the security problems inherent in other approaches. We furthermore claim (backed up by some initial results) that user-level extensibility is possible at a performance that is similar to in-kernel extensions. Finally, user-level extensions allow the use of modern software engineering techniques.