CopyCat：对飞地的受控指令级攻击
CopyCat: Controlled Instruction-Level Attacks on Enclaves
摘要：
可信执行环境（TEE）提出的对抗模型促使研究人员研究不寻常的攻击向量。一类特别强大的受控通道攻击滥用页表修改来以页级粒度可靠地跟踪飞地存储器访问。与嘈杂的微架构时序泄漏相反，这一系列确定性受控通道攻击滥用了不可或缺的架构接口，因此无法通过调整微架构资源来缓解。我们提出了一种创新的受控通道攻击，名为CopyCat，确定性地计算在单个飞地代码页内执行的指令数。我们表明，通过将CopyCat收获的指令计数与传统的粗粒度页级泄漏相结合，可以在最大的隔离级粒度下准确重建飞地控制流。CopyCat可以识别最终可能仅在单个指令中有所不同的页内和高速缓存行内分支决策，强调即使是极其细微的控制流偏差也可能从安全飞地中确定性地泄漏。我们通过对针对加密实现的单迹和确定性攻击的广泛研究，展示了CopyCat在英特尔SGX上的更高分辨率和实用性，并给出了利用广泛使用的加密库的最新版本中的微妙漏洞执行单迹密钥提取的新颖算法攻击。我们的研究结果强调了对加密实现进行更严格验证的重要性，特别是在TEE的背景下。
英文摘要：
The adversarial model presented by trusted execution environments (TEEs) has prompted researchers to investigate unusual attack vectors. One particularly powerful class of controlled-channel attacks abuses page-table modifications to reliably track enclave memory accesses at a page-level granularity. In contrast to noisy microarchitectural timing leakage, this line of deterministic controlled-channel attacks abuses indispensable architectural interfaces and hence cannot be mitigated by tweaking microarchitectural resources. We propose an innovative controlled-channel attack, named CopyCat, that deterministically counts the number of instructions executed within a single enclave code page. We show that combining the instruction counts harvested by CopyCat with traditional, coarse-grained page-level leakage allows the accurate reconstruction of enclave control flow at a maximal instruction-level granularity. CopyCat can identify intra-page and intra-cache line branch decisions that ultimately may only differ in a single instruction, underscoring that even extremely subtle control flow deviations can be deterministically leaked from secure enclaves. We demonstrate the improved resolution and practicality of CopyCat on Intel SGX in an extensive study of single-trace and deterministic attacks against cryptographic implementations, and give novel algorithmic attacks to perform single-trace key extraction that exploit subtle vulnerabilities in the latest versions of widely-used cryptographic libraries. Our findings highlight the importance of stricter verification of cryptographic implementations, especially in the context of TEEs.
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