Revisiting Virtual Memory Support for Confidential Computing Environments

Confidential computing is increasingly becoming a cornerstone for securely utilizing remote services and building trustworthy cloud infrastructure. Confidential computing builds on hardware-anchored root-of-trust that can attest the identity and authenticity of the remote machine, the configuration, and the running software stack, in an unforgeable way. In addition to the hardware-rooted verifiable attestation mechanism, confidential computing depends on strict run-time isolation of confidential computing tasks' data and code from each other and the other tasks, including privileged ones. Such isolation is achieved via on-chip access control and cryptographically once off-chip. Despite the wide support of confidential computing in most modern processors, e.g., AMD SEV-SNP and ARM CCA, there is minimal discussion of the effect of such support on the performance of conventional on-chip access control. Thus, in this paper we highlight the key changes in virtual memory support required for access control in confidential computing environments, and quantify their overheads. We propose an optimized design that enables improved performance by caching confidential computing access control metadata effectively. Two design options are proposed to balance hardware overhead and performance. We evaluate two configurations with different TLB entry coverage, which mirror Arm CCA GPC and AMD RMP, respectively. Our design improves performance by 12% over the baseline access control design and 6% over the state-of-the-art.