SPECWANDS: An Efficient Priority-based Scheduler Against Speculation Contention Attacks

TL;DR

This paper introduces SPECWANDS, a priority-based scheduler that mitigates volatile-type speculative execution attacks by preventing resource contention-based covert channels, achieving effective security with minimal performance overhead.

Contribution

It proposes a novel scheduling scheme, SPECWANDS, with three priority policies to defend against contention-based attacks while maintaining high performance.

Findings

Significant reduction in covert channel transmission.

Lower overhead compared to existing mitigation schemes.

Maintains most benefits of speculative execution.

Abstract

Transient Execution Attacks (TEAs) have gradually become a major security threat to modern high-performance processors. They exploit the vulnerability of speculative execution to illegally access private data, and transmit them through timing-based covert channels. While new vulnerabilities are discovered continuously, the covert channels can be categorised to two types: 1) Persistent Type, in which covert channels are based on the layout changes of buffering, e.g. through caches or TLBs; 2) Volatile Type, in which covert channels are based on the contention of sharing resources, e.g. through execution units or issuing ports. The defenses against the persistent-type covert channels have been well addressed, while those for the volatile-type are still rather inadequate. Existing mitigation schemes for the volatile type such as Speculative Compression and Time-Division-Multiplexing will introduce significant overhead due to the need to stall the pipeline or to disallow resource sharing. In this paper, we look into such attacks and defenses with a new perspective, and propose a scheduling-based mitigation scheme, called SPECWANDS. It consists of three priority-based scheduling policies to prevent an attacker from transmitting the secret in different contention situations. SPECWANDS not only can defend against both inter-thread and intra-thread based attacks, but also can keep most of the performance benefit from speculative execution and resource-sharing. We evaluate its runtime overhead on SPEC 2017 benchmarks and realistic programs. The experimental results show that SPECWANDS has a significant performance advantage over the other two representative schemes.