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.

在基于云的无服务器计算中，应用程序由互不信任的各方提供的多个功能组成。对于安全的无服务器计算，基于硬件的可信执行环境（TEE）可以提供功能之间的强隔离。然而，不仅要保护每个功能免受主机操作系统和其他功能的影响，还要保护主机系统免受这些功能的影响，这对于云服务器的安全至关重要。这种新兴的可信无服务器计算提出了新的挑战：每个TEE必须与主机系统双向隔离，并且来自它的系统调用必须经过验证。此外，每个TEE的资源利用必须以相互信任的方式负责。然而，当前的TEE模型无法有效地表示这种可信的无服务器应用程序。为了克服缺乏此类硬件支持的问题，本文提出了一种名为Cloister的扩展 TEE 模型，专为可信无服务器计算而设计。Cloister提出了四项新的关键技术。首先，它扩展了 SGX 中基于硬件的内存隔离，将部署的功能仅限制在其 TEE（飞地）内。其次，它提出了一个可信的监控飞地，用于过滤和验证来自飞地的系统调用。第三，它为飞地提供了服务开发人员和云提供商都认可的可信资源核算机制。最后，Cloister通过重新设计内存验证来加速 enclave 加载，以实现快速功能部署。本文使用模拟的 Intel SGX 平台和建议的扩展，表明只需对 SGX 硬件进行少量更改即可有效支持可信无服务器应用程序。