An Historical Analysis of the SEAndroid Policy Evolution

Android adopted SELinux's mandatory access control (MAC) mechanisms in 2013. Since then, billions of Android devices have benefited from mandatory access control security policies. These policies are expressed in a variety of rules, maintained by Google and extended by Android OEMs. Over the years, the rules have grown to be quite complex, making it challenging to properly understand or configure these policies. In this paper, we perform a measurement study on the SEAndroid repository to understand the evolution of these policies. We propose a new metric to measure the complexity of the policy by expanding policy rules, with their abstraction features such as macros and groups, into primitive "boxes", which we then use to show that the complexity of the SEAndroid policies has been growing exponentially over time. By analyzing the Git commits, snapshot by snapshot, we are also able to analyze the "age" of policy rules, the trend of changes, and the contributor composition. We also look at hallmark events in Android's history, such as the "Stagefright" vulnerability in Android's media facilities, pointing out how these events led to changes in the MAC policies. The growing complexity of Android's mandatory policies suggests that we will eventually hit the limits of our ability to understand these policies, requiring new tools and techniques.Comment: 16 pages, 11 figures, published in ACSAC '1

Towards a formally verified microkernel using the VCC verifier

In this thesis we present the design by contract modular approach to formal verification of an industrial real-time microkernel which was not designed with formal verification in mind. The microkernel module targeted is a particular interrupt manager of xLuna Real Time Operating System (RTOS) for embedded systems built by Critical Software S.A. The annotations were verified automatically using the Microsoft Research Verified C Compiler (VCC) tool to reason about concurrency and safety properties of xLuna kernel. The specifications are based in Hoare-style pre- and post-conditions inlined with the real code. xLuna is a microkernel based on the RTEMS Real-Time Operating System. xLuna extends RTEMS for run a GNU/Linux Operating System, providing a runtime multitasking environment for real-time (RTEMS) and non-real-time (Linux) applications. xLuna runs in a preemptable and concurrent environment. Therefore, we use VCC for reasoning about concurrent executions and some functional and safety properties of xLuna microkernel. VCC is an automated verifier for concurrent C programs that is being developed by Microsoft Research, Redmond, USA and European Microsoft Innovation Center (EMIC), Aachen, Germany. VCC is being built and used for operating system verification which makes it suitable for our verification work. Specifications were added to xLuna code following a modular approach to the verification of a specific microkernel module, namely the Interrupt Request (IRQ) module. The Verified C Compiler (VCC) annotations added cover approximately 80% of the IRQ manager C code (the remaining 20% of the code are relative to auxiliary functions outside the scope of our verification work). All the annotations were automatically verified and proven to be correct

Analyzing Security-Enhanced Linux policy specifications

NSA's Security-Enhanced (SE) Linux enhances Linux by providing a specification language for security policies and a Flask-like architecture with a security server for enforcing policies defined in the language. It is natural for users to expect to be able to analyze the properties of a policy from its specification in the policy language. But this language is very low level, making the high level properties of a policy difficult to deduce by inspection. For this reason, tools to help users with the analysis are necessary. The NRL project on analyzing SE Linux policies aims first to use mechanized support to analyze an example policy specification and then to customize this support for use by practitioners in the open source software community. This paper describes how we model policies in the analysis tool TAME, the kinds of analysis we can support, and prototype mechanical support to enable others to model their policies in TAME. The paper concludes with some general observations on desirable properties for a policy language