Mr-TEE: Practical Trusted Execution of Mixed-Criticality Code

Abstract

Industry 4.0 is increasingly using commodity hardware and software in place of dedicated control systems to lower costs and increase flexibility. However, this means that critical control code must compete for resources with an increasingly complex software stack that exposes a new attack surface. The Mixed Criticality Trusted Execution Environment (Mr-TEE) tackles this problem at its root, by delivering availability for safety-critical control code, while running untrusted applications in a minimally modified Linux stack. This is achieved by providing a real-time scheduler and novel peripheral sharing system in the Secure World. Mr-TEE hence provides the best of both worlds for Industry 4.0 developers, ensuring the trusted execution of time-sensitive control applications, while minimizing design effort and restrictions for untrusted applications. Evaluation on an Arm TrustZone-enabled Cortex MCU demonstrates a worst-case overhead of 1.88% to support real-time scheduling in the TEE.