Verifying Policy Enforcers

TL;DR

This paper introduces a verification strategy to detect and prevent interference among multiple policy enforcers in software systems, ensuring their safe coexistence at runtime.

Contribution

We propose a novel verification approach that identifies potential conflicts between sets of policy enforcers before deployment.

Findings

Discovered incompatibilities among Android policy enforcers

Verified the effectiveness of the method in predicting enforcer interference

Enhanced safety in runtime policy enforcement

Abstract

Policy enforcers are sophisticated runtime components that can prevent failures by enforcing the correct behavior of the software. While a single enforcer can be easily designed focusing only on the behavior of the application that must be monitored, the effect of multiple enforcers that enforce different policies might be hard to predict. So far, mechanisms to resolve interferences between enforcers have been based on priority mechanisms and heuristics. Although these methods provide a mechanism to take decisions when multiple enforcers try to affect the execution at a same time, they do not guarantee the lack of interference on the global behavior of the system. In this paper we present a verification strategy that can be exploited to discover interferences between sets of enforcers and thus safely identify a-priori the enforcers that can co-exist at run-time. In our evaluation, we experimented our verification method with several policy enforcers for Android and discovered some incompatibilities.