Revizor: Testing Black-box CPUs against Speculation Contracts

TL;DR

Revizor is a novel testing framework that automatically detects speculative execution vulnerabilities in black-box CPUs by verifying compliance with speculation contracts, revealing known and unknown security issues.

Contribution

It introduces a model-based relational testing approach and implements it in Revizor to systematically identify microarchitectural leaks in commercial CPUs.

Findings

Revizor successfully detected Spectre, MDS, and LVI vulnerabilities.

It uncovered several previously unknown speculative execution variants.

The framework demonstrated effectiveness on real Intel x86 CPUs.

Abstract

Speculative vulnerabilities such as Spectre and Meltdown expose speculative execution state that can be exploited to leak information across security domains via side-channels. Such vulnerabilities often stay undetected for a long time as we lack the tools for systematic testing of CPUs to find them. In this paper, we propose an approach to automatically detect microarchitectural information leakage in commercial black-box CPUs. We build on speculation contracts, which we employ to specify the permitted side effects of program execution on the CPU's microarchitectural state. We propose a Model-based Relational Testing (MRT) technique to empirically assess the CPU compliance with these specifications. We implement MRT in a testing framework called Revizor, and showcase its effectiveness on real Intel x86 CPUs. Revizor automatically detects violations of a rich set of contracts, or indicates their absence. A highlight of our findings is that Revizor managed to automatically surface Spectre, MDS, and LVI, as well as several previously unknown variants.