SpecCFA：通过应用感知的子路径推测增强控制流证明/审计
SpecCFA: Enhancing Control Flow Attestation/Auditing via Application-Aware Sub-Path Speculation
AI总结：
针对MCU控制流证明中CFLog存储与传输成本高的问题，提出SpecCFA方法，利用程序特定的可预测子路径进行动态推测优化，在保留安全保证的同时显著降低存储与性能开销。
摘要：
在现代信息物理系统的边缘，微控制器单元（MCU）负责安全关键的传感/执行。然而，MCU的成本约束排除了通用计算机常用的安全机制。因此，人们提出了各种低成本安全架构来远程验证MCU软件完整性。控制流证明（CFA）使验证器（Vrf）能够远程评估证明器MCU（Prv）的运行时行为，生成Prv所有控制流转换（CFLog）的认证轨迹。此外，控制流审计架构通过保证将证据交付给Vrf来增强CFA。不幸的是，现有CFA的局限性在于存储和传输CFLog的成本，因为即使是简单的MCU软件也可能生成大量轨迹。鉴于这些问题，先前的工作提出了静态（上下文不敏感）优化。然而，它们不支持可配置的特定程序优化。在这项工作中，我们注意到程序可能产生独特的可预测控制流子路径，并认为可以利用特定程序的可预测性来动态优化CFA，同时保留所有安全保证。因此，我们提出SpecCFA：一种在CFA中进行动态子路径推测的方法。SpecCFA允许Vrf安全地推测每个被证明程序的可能控制流子路径。在运行时，当CFLog中的子路径匹配预定义的推测时，整个子路径将被替换为一个保留符号。SpecCFA可以同时推测多个可变长度的控制流子路径。我们在两个开源控制流审计架构上实现了SpecCFA：一个基于定制硬件设计，另一个基于商用可信执行环境（ARM TrustZone-M）。在这两种情况下，SpecCFA显著降低了存储/性能成本，这对于资源受限的MCU至关重要。
英文摘要：
At the edge of modern cyber-physical systems, Micro-Controller Units (MCUs) are responsible for safety-critical sensing/actuation. However, MCU cost constraints rule out the usual security mechanisms of general-purpose computers. Thus, various low-cost security architectures have been proposed to remotely verify MCU software integrity. Control Flow Attestation (CFA) enables a Verifier (Vrf) to remotely assess the run-time behavior of a prover MCU (Prv), generating an authenticated trace of all of Prv control flow transfers (CFLog). Further, Control Flow Auditing architectures augment CFA by guaranteeing the delivery of evidence to Vrf. Unfortunately, a limitation of existing CFA lies in the cost to store and transmit CFLog, as even simple MCU software may generate large traces. Given these issues, prior work has proposed static (context-insensitive) optimizations. However, they do not support configurable program-specific optimizations. In this work, we note that programs may produce unique predictable control flow sub-paths and argue that program-specific predictability can be leveraged to dynamically optimize CFA while retaining all security guarantees. Therefore, we propose SpecCFA: an approach for dynamic sub-path speculation in CFA. SpecCFA allows Vrf to securely speculate on likely control flow sub-paths for each attested program. At run-time, when a sub-path in CFLog matches a pre-defined speculation, the entire sub-path is replaced by a reserved symbol. SpecCFA can speculate on multiple variable-length control flow sub-paths simultaneously. We implement SpecCFA atop two open-source control flow auditing architectures: one based on a custom hardware design and one based on a commodity Trusted Execution Environment (ARM TrustZone-M). In both cases, SpecCFA significantly lowers storage/performance costs that are critical to resource-constrained MCUs.
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