Poster: Entropy-Coupled CLFLUSH for Secure Cache Flushing Against Timing-Based Attacks

Modern cache flush instructions, such as CLFLUSH, are essential for coherence and persistence but introduce deterministic timing behavior exploitable in attacks like Flush+Reload. We present Entropy-Coupled CLFLUSH (E-Flush), a secure redesign that integrates hardware entropy into the flush pipeline to randomize its latency and traversal order. By coupling each flush invocation with a unique entropy token, E-Flush eliminates observable timing patterns without affecting architectural correctness. Formal analysis proves zero timing leakage, and cycle-accurate simulation demonstrates less than 2.5% performance overhead. E-Flush thus provides a low-cost, backward-compatible defense against flush-based microarchitectural side channels.