Randomizing Set-Associative Caches Against Conflict-Based Cache Side-Channel Attacks

Conflict-based cache side-channel attacks against the last-level cache (LLC) is a widely exploited method for information leaking. Cache randomization has recently been accepted as a promising defense. Most of recent designs randomize skewed caches rather than classic set-associative caches; however, skewed caches incur substantial performance overhead both in area and runtime. We cautiously argue that randomized set-associative caches can be sufficiently strengthened and possess a better chance to be adopted in the near future. For the first time, a dynamically randomized set-associative cache has been implemented in the LLC of a Linux capable multicore processor. A single-cycle hash logic is designed for randomizing the cache set indices. A multi-step relocation scheme is used to reduce the cost in remapping the cache layout. The randomized cache layout is remapped periodically for limiting the time window available to attackers. An attack detector is implemented to catch attacks in action and consequently trigger extra remaps. The evaluation results show that the randomized LLC has been sufficiently strengthened to thwart all existing fast algorithms for searching eviction sets with only marginal runtime overhead, and small area and power overhead.