MicroScope: Enabling Microarchitectural Replay Attacks

The popularity of hardware-based Trusted Execution Environments (TEEs) has recently skyrocketed with the introduction of Intel's Software Guard Extensions (SGX). In SGX, the user process is protected from supervisor software, such as the operating system, through an isolated execution environment called an enclave. Despite the isolation guarantees provided by TEEs, numerous microarchitectural side channel attacks have been demonstrated that bypass their defense mechanisms. But, not all hope is lost for defenders: many modern fine-grain, high-resolution side channels-e.g., execution unit port contention-introduce large amounts of noise, complicating the adversary's task to reliably extract secrets. In this work, we introduce Microarchitectural Replay Attacks, whereby an SGX adversary can denoise nearly arbitrary microar- chitectural side channels in a single run of the victim, by causing the victim to repeatedly replay on a page faulting instruction. We design, implement, and demonstrate our ideas in a framework, called MicroScope, and use it to denoise notoriously noisy side channels. Our main result shows how MicroScope can denoise the execution unit port contention channel. Specifically, we show how Micro- Scope can reliably detect the presence or absence of as few as two divide instructions in a single logical run of the victim program. Such an attack could be used to detect subnormal input to individual floating-point instructions, or infer branch directions in an enclave despite today's countermeasures that flush the branch predictor at the enclave boundary. We also use MicroScope to single-step and denoise a cache-based attack on the OpenSSL implementation of AES. Finally, we discuss the broader implications of microarchitec- tural replay attacks-as well as discuss other mechanisms that can cause replays.