Complementing Confidential Computing Environment for Applications on Arm CCA

TrustZone is a promising security technology for the use of partitioning sensitive data into a trusted execution environment (TEE). Unfortunately, third-party developers have limited access to TrustZone. Advanced virtualization-based TEE introduced in the recent Arm Confidential Compute Architecture (CCA) creates a new physical address space called Realm world for confidential computing to protect data confidentiality and integrity of third-party. However, the current CCA primarily targets the VM level in the Realm world and does not provide a confidential computing environment for applications. To fill up this gap, we present SHELTER, which is a complement to CCA's primary Realm VM-style architecture. SHELTER allows third-party developers to deploy their applications with isolation. SHELTER is designed by cooperating with Arm CCA hardware primitive to provide hardware-based isolation while removing the need for software workloads to trust their data to a Host OS, hypervisor, or privileged software. We also design a device assignment mechanism that enables applications running in SHELTER to gain protected peripheral isolation. We have implemented and evaluated SHELTER, and the results demonstrated that SHELTER not only guarantees the isolation of applications in userspace but also incurs no more than 15% performance overhead on real-world workloads.