Programmable logic controllers (PLCs) are crucial devices for implementing automated control in various industrial control systems (ICS), such as smart power grids, water treatment systems, manufacturing, and transportation systems. Owing to their importance, PLCs are often the target of cyber attackers that are aiming at disrupting the operation of ICS, including the nation's critical infrastructure, by compromising the integrity of control logic execution. While a wide range of cybersecurity solutions for ICS have been proposed, they cannot counter strong adversaries with a foothold on the PLC devices, which could manipulate memory, I/O interface, or PLC logic itself. These days, many ICS devices in the market, including PLCs, run on ARM-based processors, and there is a promising security technology called ARM TrustZone, to offer a Trusted Execution Environment (TEE) on embedded devices. Envisioning that such a hardware-assisted security feature becomes available for ICS devices in the near future, this paper investigates the application of the ARM TrustZone TEE technology for enhancing the security of PLC. Our aim is to evaluate the feasibility and practicality of the TEE-based PLCs through the proof-of-concept design and implementation using open-source software such as OP-TEE and OpenPLC. Our evaluation assesses the performance and resource consumption in real-world ICS configurations, and based on the results, we discuss bottlenecks in the OP-TEE secure OS towards a large-scale ICS and desired changes for its application on ICS devices. Our implementation is made available to public for further study and research.

翻译：可编程逻辑控制器（PLC）是智能电网、水处理系统、制造业和交通运输系统等各类工业控制系统（ICS）中实现自动化控制的关键设备。由于其重要性，PLC常成为网络攻击者的目标，他们试图通过破坏控制逻辑执行的完整性来扰乱ICS的运行，包括国家关键基础设施。虽然已提出多种针对ICS的网络安全解决方案，但这些方案无法对抗已渗透PLC设备的强大攻击者——此类攻击者能够篡改内存、I/O接口或PLC逻辑本身。当前市场中许多ICS设备（包括PLC）均采用基于ARM架构的处理器，而ARM TrustZone作为一种具有前景的安全技术，可为嵌入式设备提供可信执行环境（TEE）。基于此类硬件辅助安全功能即将应用于ICS设备的预期，本文研究了ARM TrustZone TEE技术在增强PLC安全性方面的应用。我们旨在通过基于OP-TEE和OpenPLC等开源软件的概念验证设计与实现，评估基于TEE的PLC的可行性与实用性。实验评估了真实ICS配置下的性能与资源消耗，并根据评估结果讨论了OP-TEE安全操作系统在大规模ICS中的应用瓶颈，以及其在ICS设备上应用所需的改进方向。我们的实现已公开发布，以供进一步研究参考。