Cross-core cache timing side-channel attacks, which observe cache access behavior of victims running on different physical cores to infer sensitive information, have become a significant threat. Although the attacks are covert, they cause the attacked cachelines to frequently migrate among cache hierarchies, rendering abnormal traffic. Based on this observation, the proposed scheme PiPoMonitor records cache-memory access traffic and prefetch suspicious lines under attack to interfere with adversaries’ probes. In pursuit of security and performance, PiPoMonitor exploits a Cuckoo filter as the recording structure and introduces two features to it: 1) autonomic deletion and 2) relocation accelerating. The former exponentially increases the uncertainty of record eviction against reverse engineering attacks, while the latter leverages a pipelined architecture to alleviate the impact of intensive filter queries on the memory critical path. PiPoMonitor is not only able to effectively mitigate cross-core cache attacks and defeat sophisticated defense-aware attackers but also induces a negligible performance penalty and acceptable hardware overhead.

Cache side channel attacks obtain victim cache line access footprint to infer security-critical information. Among them, cross-core attacks exploiting the shared last level cache are more threatening as their simplicity to set up and high capacity. Stateful approaches of detection-based mitigation observe precise cache behaviors and protect specific cache lines that are suspected of being attacked. However, their recording structures incur large storage overhead and are vulnerable to reverse engineering attacks. Exploring the intrinsic non-determinate layout of a traditional Cuckoo filter, this paper proposes a space efficient Auto-Cuckoo filter to record access footprints, which succeed to decrease storage overhead and resist reverse engineering attacks at the same time. With Auto-Cuckoo filter, we propose PiPoMonitor to detect Ping-Pong patterns and prefetch specific cache line to interfere with adversaries' cache probes. Security analysis shows the PiPoMonitor can effectively mitigate cross-core attacks and the Auto-Cuckoo filter is immune to reverse engineering attacks. Evaluation results indicate PiPoMonitor has negligible impact on performance and the storage overhead is only 0.37%, an order of magnitude lower than previous stateful approaches.

Continuous Attacks are common cross-core cache side-channel attack scenarios that we observed, where adversaries frequently probe-target cache lines in a short time. Under Continuous Attacks, the attacked lines go through multiple load-evict processes between different cache (or memory) hierarchies, exhibiting Ping-Pong patterns. Identifying and obscuring these abnormal patterns effectively interfere with the attacker's probe and mitigate such attacks. Our recent proposal, Ping-Pong regulator (PPR), captures multiple Ping-Pong patterns by counting the reaccesses per cache line and blocks them with different obscuring actions (preload or lock). Although PPR mitigates Continuous Attacks, the added regulator directory (RDir) is vulnerable because it cannot record all cache lines simultaneously. Sophisticated attackers can evict the records of the attacked line from the RDir to avoid triggering defensive actions, thereby bypassing PPR. To improve robustness, we further propose PPR+, which dynamically changes the mapping of physical addresses to RDir locations by encryption and periodically changing keys. This randomness makes it difficult for attackers to evict target entries out of the RDir within a limited time. We show that PPR+ tolerates more than 100 years of attacks, induces negligible performance impacts (improves 0.13%), requires acceptable storage overhead (3.15%), and does not need any software support.

In this paper, we observed Continuous Attacks are one kind of common side channel attack scenarios, where an adversary frequently probes the same target cache lines in a short time. Continuous Attacks cause target cache lines to go through multiple load-evict processes, exhibiting Ping-Pong Patterns. Identifying and obscuring Ping-Pong Patterns effectively interferes with the attacker’s probe and mitigates Continuous Attacks. Based on the observations, this paper proposes Ping-Pong Regulator to identify multiple Ping-Pong Patterns and block them with different strategies (Preload or Lock). The Preload proactively loads target lines into the cache, causing the attacker to mistakenly infer that the victim has accessed these lines; the Lock fixes the attacked lines’ directory entries on the last level cache directory until they are evicted out of caches, making an attacker’s observation of the locked lines is always the L2 cache miss. The experimental evaluation demonstrates that the Ping-Pong Regulator efficiently identifies and secures attacked lines, induces negligible performance impacts and storage overhead, and does not require any software support.

Modern processor cores share the last-level cache and directory to improve resource utilization. Unfortunately, such sharing makes the cache vulnerable to cross-core cache side channel attacks. Recent studies show that information leakage through cross-core cache side channel attacks is a serious threat in different computing domains ranging from cloud servers and mobile phones to embedded devices. However, previous solutions have limitations of losing performance, lacking golden standards, requiring software support, or being easily bypassed.