Attack Directories on ARM big.LITTLE Processors

Eviction-based cache side-channel attacks take advantage of inclusive cache hierarchies and shared cache hardware. Processors with the template ARM big.LITTLE architecture do not guarantee such preconditions and therefore will not usually allow cross-core attacks let alone cross-cluster attacks. This work reveals a new side-channel based on the snoop filter (SF), an unexplored directory structure embedded in template ARM big.LITTLE processors. Our systematic reverse engineering unveils the undocumented structure and property of the SF, and we successfully utilize it to bootstrap cross-core and cross-cluster cache eviction. We demonstrate a comprehensive methodology to exploit the SF side-channel, including the construction of eviction sets, the covert channel, and attacks against RSA and AES. When attacking TrustZone, we conduct an interrupt-based side-channel attack to extract the key of RSA by a single profiling trace, despite the strict cache clean defense. Supported by detailed experiments, the SF side-channel not only achieves competitive performance but also overcomes the main challenge of cache side-channel attacks on ARM big.LITTLE processors.