Countermeasures for cache contention-based attacks based on randomisation remapping

Abstract

Many cache designs have been proposed to guard against contention-based side-channel attacks. Specifically, the last-level cache, which is often a shared cache between different users. One type of well-known cache is the randomisation remapping cache. For example, the CEASER-S cache applies an encryption cypher with a periodically changing key as a cache indexing function. By decreasing the re-keying period, CEASER-S can defeat even a more aggressive contention-based attack. However, this can lead to performance degradation. Balancing the performance and the security against contention-based attacks becomes an essential consideration of the cache design. In this thesis, we propose a novel cache configuration, logical associativity. By applying this configuration, we propose two secure randomisation remapping cache designs against contention-based attacks. The first cache we propose is the CEASER-SH cache, which is based on the CEASER-S cache. This cache allows the cache line to be placed not only in its mapped cache set but also in the subsequent cache sets. By enlarging the possible placement positions of the cache line, contention-based attacks are mitigated. Hence, the cache does not need to decrease the re-keying period significantly which would cause significant performance degradation. From the simulation results, for example, compared with CEASER-S, CEASER-SH with a logical associativity of 2 can reduce the miss rate by about 26% and the CPI by about 0.8% while maintaining the same security level against an aggressive Prime+Probe attack. The second secure cache we propose is the Skewed Elastic-Associativity Cache (SEA cache). Unlike from CEASER-SH, this cache allows each user or each process to have different local logical associativity settings. Hence, only some users or processes that request extra protection against contention-based attacks are protected with high logical associativity. Other users can access the cache, or other pages can be accessed in the cache with lower latency and higher performance. The simulation results show that the SEA cache can outperform the CEASER-SH cache in terms of normal user’s performance and overall security against contention-based attacks with minor extra power consumption. For example, the SEA cache with logical associativity of 1 for normal protection users and 16 for high protection users achieves better protection against contention-base attacks and about 0.4% CPI degredation in the normal user’s core with just 0.01W extra power, compared to the CEASER-SH cache with logical associativity of 8.

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Identifiers

ORCID for Xiao Liu: orcid.org/0000-0002-5928-4293

ORCID for Mark Zwolinski: orcid.org/0000-0002-2230-625X

ORCID for Basel Halak: orcid.org/0000-0003-3470-7226

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