Hardware-hardened Sandbox Enclaves for Trusted Serverless Computing

Abstract

In cloud-based serverless computing, an application consists of multiple functions provided by mutually distrusting parties. For secure serverless computing, the hardware-based trusted execution environment (TEE) can provide strong isolation among functions. However, not only protecting each function from the host OS and other functions, but also protecting the host system from the functions, is critical for the security of the cloud servers. Such an emerging trusted serverless computing poses new challenges: Each TEE must be isolated from the host system bi-directionally, and the system calls from it must be validated. In addition, the resource utilization of each TEE must be accountable in a mutually trusted way. However, the current TEE model cannot efficiently represent such trusted serverless applications. To overcome the lack of such hardware support, this article proposes an extended TEE model called Cloister, designed for trusted serverless computing. Cloister proposes four new key techniques. First, it extends the hardware-based memory isolation in SGX to confine a deployed function only within its TEE (enclave). Second, it proposes a trusted monitor enclave that filters and validates system calls from enclaves. Third, it provides a trusted resource accounting mechanism for enclaves that is agreeable to both service developers and cloud providers. Finally, Cloister accelerates enclave loading by redesigning its memory verification for fast function deployment. Using an emulated Intel SGX platform with the proposed extensions, this article shows that trusted serverless applications can be effectively supported with small changes in the SGX hardware.