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Nemesis: Studying microarchitectural timing leaks in rudimentary CPU interrupt logic

This repository contains the source code accompanying our paper on interrupt timing attacks which appears in the 25th ACM Conference on Computer and Communications Security (CCS'18).

Jo Van Bulck, Frank Piessens, and Raoul Strackx. 2018. Nemesis: Studying Microarchitectural Timing Leaks in Rudimentary CPU Interrupt Logic. In Proceedings of the 25th ACM Conference on Computer and Communications Security (CCS'18).

Abstract

Recent research on transient execution vulnerabilities shows that current processors exceed our levels of understanding. The prominent Meltdown and Spectre attacks abruptly revealed fundamental design flaws in CPU pipeline behavior and exception handling logic, urging the research community to systematically study attack surface from microarchitectural interactions.

We present Nemesis, a previously overlooked side-channel attack vector that abuses the CPU's interrupt mechanism to leak microarchitectural instruction timings from enclaved execution environments such as Intel SGX, Sancus, and TrustLite. At its core, Nemesis abuses the same subtle microarchitectural behavior that enables Meltdown, i.e., exceptions and interrupts are delayed until instruction retirement. We show that by measuring the latency of a carefully timed interrupt, an attacker controlling the system software is able to infer instruction-granular execution state from hardware-enforced enclaves. In contrast to speculative execution vulnerabilities, our novel attack vector is applicable to the whole computing spectrum, from small embedded sensor nodes to high-end commodity x86 hardware. We present practical interrupt timing attacks against the open-source Sancus embedded research processor, and we show that interrupt latency reveals microarchitectural instruction timings from off-the-shelf Intel SGX enclaves. Finally, we discuss challenges for mitigating Nemesis-type attacks at the hardware and software levels.

Source code overview

We evaluated interrupt timing attacks on two case study platforms.

• Sancus: this directory contains source code for the secure keypad and BSL applications scenarios plus corresponding attacker code. Note that the secure interrupt architectural extensions we implemented for this work have been upstreamed to the open-source sancus-core and sancus-compiler repositories.

• Intel SGX: this directory contains source code for the microbenchmarks, binary search, and Zigzagger enclave evaluation scenarios plus corresponding attacker code and post-processing scripts. Note that the single-stepping framework enhancements we developed for this work have been upstreamed to the open-source SGX-Step repository.

License

All Nemesis code is free software, licensed under GPLv3.