GhostMinion: A Strictness-Ordered Cache System for Spectre Mitigation

TL;DR

GhostMinion introduces a novel cache system implementing Strictness Ordering to effectively mitigate Spectre attacks while maintaining high performance with only 2.5% overhead.

Contribution

The paper proposes Strictness Ordering as a new constraint system and presents GhostMinion, a cache modification that achieves comprehensive Spectre mitigation with minimal performance impact.

Findings

Effectively eliminates transient side channel attacks.

Achieves only 2.5% performance overhead.

Supports complex speculation and data forwarding.

Abstract

Out-of-order speculation, a technique ubiquitous since the early 1990s, remains a fundamental security flaw. Via attacks such as Spectre and Meltdown, an attacker can trick a victim, in an otherwise entirely correct program, into leaking its secrets through the effects of misspeculated execution, in a way that is entirely invisible to the programmer's model. This has serious implications for application sandboxing and inter-process communication. Designing efficient mitigations, that preserve the performance of out-of-order execution, has been a challenge. The speculation-hiding techniques in the literature have been shown to not close such channels comprehensively, allowing adversaries to redesign attacks. Strong, precise guarantees are necessary, but at the same time mitigations must achieve high performance to be adopted. We present Strictness Ordering, a new constraint system that shows how we can comprehensively eliminate transient side channel attacks, while still allowing complex speculation and data forwarding between speculative instructions. We then present GhostMinion, a cache modification built using a variety of new techniques designed to provide Strictness Order at only 2.5% overhead.