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Abstract—Protection of cache hierarchies from side-channel attacks is critical for building secure systems, particularly the ones using Trusted Execution Environments (TEEs). In this pa- per, we consider the problem of efficient and secure fine-grained partitioning of cache hierarchies and propose a framework, called Secure Hierarchies for TEEs (TEE-SHirT). In the context of a three-level cache system, TEE-SHirT consists of partitioned shared last-level cache, partitioned private L2 caches, and non- partitioned L1 caches that are flushed on context switches and system calls. Efficient and correct partitioning requires careful design. Towards this goal, TEE-SHirT makes three contributions: 1) we demonstrate how the hardware structures used for holding cache partitioning metadata can be effectively virtualized to avoid flushing of cache partition content on context switches and system calls; 2) we show how to support multi-threaded enclaves in TEE- SHirT, addressing the issues of coherency and consistency that arise with both intra-core and inter-core data sharing; 3) we develop a formal security model for TEE-SHirT to rigorously reason about the security of our design. 

The security of isolated execution architectures such as Intel SGX has been significantly threatened by the recent emer- gence of side-channel attacks. Cache side-channel attacks allow adversaries to leak secrets stored inside isolated en- claves without having direct access to the enclave memory. In some cases, secrets can be leaked even without having the knowledge of the victim application code or having OS-level privileges. We propose the concept of Composable Cachelets (CC), a new scalable strategy to dynamically partition the last-level cache (LLC) for completely isolating enclaves from other applications and from each other. CC supports enclave isolation in caches with the capability to dynamically readjust the cache capacity as enclaves are created and destroyed. We present a cache-aware and enclave-aware operational seman- tics to help rigorously establish security properties of CC, and we experimentally demonstrate that CC thwarts side-channel attacks on caches with modest performance and complexity impact.