Thwarting Cache Side Channel Attacks with Encryption Address-Based Set Balance Cache

Abstract

The deterministic memory-to-cache mapping used by cache side channel attack causes the leakage of sensitive information such as secret keys, which seriously threatens user security and highlights the need to defend against this kind of attack. Recent table-based secure cache design requires more space to store the entry while a purely encryption-based design needs complex encryption units to ensure robustness. What is more, the newer attack algorithm enabling faster eviction set discovery may still break such defenses. Even though increasing the association of cache can be a potential solution, it introduces too much redundancy cache access and storage overhead. In this paper, we eliminate this problem. We present Encryption address-based Set Balance Cache (ESBC), a novel cache design to mitigate cache-based side channel attack. ESBC encrypts an address into two-level sets and displaces the data from a primary set into the secondary set when the primary set is full. The two-level mapping structure increases the complexity for attackers to build eviction sets, which is a vital step for the conflict-based attack. Furthermore, we adopt two different optimized variants from a temporal perspective, ESBC with remapping (ESBCR), which serves dynamic-remapping, and spatial perspective, ESBC with multi-mapping (ESBCM), which performs multi-mapping to improve the robustness. Our security analysis reveals that these designs can confuse the exploitation of conflicting addresses. Simulation-based evaluation on SPEC2017 shows 0.24% instruction per cycle (IPC) degradation for ESBCR with 1% remap rate. While the reduction of ESBCM that has five potential secondary sets is 0.69%. What is exciting is that both miss per kilo instructions (MPKI) and miss rates are even reduced because of the efficient cache usage. The storage overhead of these two variants is only 0.87%. By comparing the two schemes, we can observe that though ESBCR brings less performance overhead, the ESBCM has better scalability.