Fooling the Sense of Cross-Core Last-Level Cache Eviction Based Attacker by Prefetching Common Sense

Abstract

Cross-core last-level cache (LLC) eviction based side-channel attacks are becoming practical because of the inclusive nature of shared resources (e.g., an inclusive LLC), that creates back-invalidation-hits at the private caches. Most of the cross-core eviction based side-channel attack strategies exploit the same for a successful attack. The fundamental principle behind all the cross-core eviction attack strategies is that the attacker can observe LLC access time differences (in terms of latency differences between events such as hits/misses) to infer about the data used by the victim. We fool the attacker (by providing LLC hits to the addresses of interest) through a back-invalidation-hits triggered hardware prefetching technique (BITP). BITP is an L2 cache level hardware prefetcher that prefetches the back-invalidated block addresses and refills the LLC (along with the L2) before the attacker's observation/access, efficiently nullifying inferences due to differences in access latencies. We show that BITP can fool the attacker with various security metrics related to LLC side-channel. BITP provides zero probability of success in terms of attacker's probability of success for Evict+Time, Evict+Reload, and Prime+Probe attacks. We also show the effectiveness of BITP in terms of performance by simulating SPEC CPU 2006, PARSEC, and CloudSuite benchmarks and find that, on average, BITP improves system performance marginally by 1.1%. Overall, BITP is a simple, practical, and yet powerful technique in mitigating various cross-core LLC eviction-based side-channel attacks. Compared to the state-of-the-art policies, BITP does not require support from software writer, operating system (OS), and runtime systems. Overall, BITP provides marginal improvement in system performance, providing security with no hardware and performance overhead, which makes BITP readily-implementable.