Stockade: Hardware Hardening for Distributed Trusted Sandboxes

Abstract

Recent studies showed that a cloud application consists of multiple distributed modules provided by mutually distrustful parties. For trusted services, such applications can use trusted execution environments (TEEs) communicating through software-encrypted memory channels. Such an emerging TEE execution model requires a new type of bi-directional protection: protecting the rest of the system from the enclave module with sandboxing and protecting the enclave module from third-party modules and the operating system. However, the current TEE model cannot efficiently represent such distributed sandbox applications. To overcome the lack of hardware supports, this paper proposes an extended TEE model called STOCKADE, which supports distributed sandboxes hardened by hardware. STOCKADE proposes new three key techniques. First, it extends the hardware-based memory isolation in SGX to confine a user software module only within its TEE (enclave). Second, it proposes a trusted monitor enclave that filters and validates systems calls from enclaves. Finally, it allows hardware-protected memory sharing between a pair of enclaves for efficient protected communication without software-based encryption. Using an emulated SGX platform with the proposed extensions, this paper shows that distributed sandbox applications can be effectively supported with small changes of SGX hardware.