Manageable fine-grained information flow

The continuing frequency and seriousness of security incidents underline the critical importance of application security. Decentralized information flow control (DIFC), a promising tool for improving application security, gives application developers fine-grained control over security policy and privilege management. DIFC developers can partition much application functionality into untrusted components bound by a kernel- or language-enforced security policy. Unless a (usually smaller and less exposed) trusted component is exploited, the effects of an application compromise are contained by the policy. Although system-based DIFC can simultaneously achieve high performance and effective isolation, it offers a challenging programming model. Fine-grained policy specifications are spread over several application pieces. Common programming errors may be indistinguishable from policy exploit attempts, the system cannot expose developers to information about these errors, complicating debugging. Static checking (as in language based systems) and new system primitives can reduce these problems, but for dynamic applications like web servers, they do not eliminate them. In this paper we propose subsystems that make decentralized information flow more manageable. First, a policy description language specifies an application-wide security policy in one localized place; communication restrictions are compiled into lower-level labels. Second, information flow-safe debugging mechanisms let developers debug DIFC applications without violating security policies. Although these mechanisms are preliminary, we demonstrate their effectiveness using applications similar to those developed for Asbestos and other DIFC systems.