  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.

Cryptography and Security;Hardware Architecture