ISC-FLAT：控制流证明与实时的操作的冲突
ISC-FLAT: On the Conflict Between Control Flow Attestation and Real-Time Operations
摘要：
物联网设备和网络物理系统（CPS）的广泛采用使得嵌入式设备变得越来越重要。虽然这些设备中的一些执行关键任务，但它们通常使用微控制器单元（MCU）实现，这些MCU缺乏与通用计算机相同的安全机制，使它们更容易受到远程攻击，从而破坏其软件完整性。受这个问题的启发，先前的工作已经提出了远程评估嵌入式MCU软件的可信度的技术。其中，控制流证明（CFA）能够远程检测在执行期间非法修改程序控制流的运行时滥用。尽管有这些进步，目前的CFA方法有一个基本的限制：它们排除了在执行被证明的软件操作期间的中断。简单地说，现有的CFA技术是不安全的，除非在MCU上禁用中断。另一方面，我们认为，缺乏可中断性可以掩盖CFA的有用性，因为大多数嵌入式应用程序依赖于中断处理异步事件的实时的【形】。为了解决这一限制，我们提出了中断安全控制流证明（ISC-FLAT）：一种CFA技术，与现有MCU兼容，并在不影响CFA报告真实性的情况下实现中断处理。与其他不需要自定义硬件修改的CFA技术类似，ISC-FLAT利用可信执行环境（TEE）（特别是，我们的原型构建在ARM TrustZone-M上）安全地生成不可伪造的CFA报告，而不会阻止应用程序处理中断。我们在ARM Cortex-M33 MCU上实现了一个功能齐全的ISC-FLAT原型，并证明与现有的基于TEE的CFA方法相比，它的运行时开销最小，不支持中断。
英文摘要：
The wide adoption of IoT gadgets and Cyber-Physical Systems (CPS) makes embedded devices increasingly important. While some of these devices perform mission-critical tasks, they are usually implemented using Micro-Controller Units (MCUs) that lack security mechanisms on par with those available to general-purpose computers, making them more susceptible to remote exploits that could corrupt their software integrity. Motivated by this problem, prior work has proposed techniques to remotely assess the trustworthiness of embedded MCU software. Among them, Control Flow Attestation (CFA) enables remote detection of runtime abuses that illegally modify the program's control flow during execution. Despite these advances, current CFA methods share a fundamental limitation: they preclude interrupts during the execution of the software operation being attested. Simply put, existing CFA techniques are insecure unless interrupts are disabled on the MCU. On the other hand, we argue that the lack of interruptability can obscure CFA usefulness, as most embedded applications depend on interrupts to process asynchronous events in real-time. To address this limitation, we propose Interrupt-Safe Control Flow Attestation (ISC-FLAT): a CFA technique that is compatible with existing MCUs and enables interrupt handling without compromising the authenticity of CFA reports. Similar to other CFA techniques that do not require customized hardware modifications, ISC-FLAT leverages a Trusted Execution Environment (TEE) (in particular, our prototype is built on ARM TrustZone-M) to securely generate unforgeable CFA reports without precluding applications from processing interrupts. We implement a fully functional ISC-FLAT prototype on the ARM Cortex-M33 MCU and demonstrate that it incurs minimal runtime overhead when compared to existing TEE-based CFA methods that do not support interrupts.
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