TreasureCache: Hiding Cache Evictions Against Side-Channel Attacks

Cache side-channel attacks remain a stubborn source of cross-core secret leakage. Such attacks exploit the timing difference between cache hits and misses. Most defenses thus choose to prevent cache evictions. Given that two possible types of evictions—flush-based and conflict-based—use different architectural features, these defenses have to integrate hybrid defense strategies, incur OS modification, and sacrifice performance to completely throttle cache side-channel attacks. In this paper, we present TreasureCache against cache side-channel attacks without modifying OS or sacrificing performance. Instead of preventing cache evictions with various costs, we advocate to allow cache evictions as is and hide exploitable evictions in our specialized small eviction-hidden buffer. The buffer guarantees a fast hit time comparative to LLC hits. This instantly closes the timing gap between accessing exploitable blocks when they are in and out of the LLC. Moreover, with the help of our buffer, we no longer have to disable flush instructions or shared memory. A lightweight constant-time flush instruction can help TreasureCache to prevent both flush-based and conflict-based side-channel attacks. We validate TreasureCache security and performance through extensive experiments. With a hardware overhead of less than 0.5%, TreasureCache reduces the secret-leakage resolution by about 1,000 times without introducing any performance slowdown.