ZION: A Practical Confidential Virtual Machine Architecture on Commodity RISC-V Processors

Trusted Execution Environments (TEEs) provide robust hardware-based isolation to mitigate data breaches and privacy risks. Confidential Virtual Machines (confidential VMs or CVMs) extend these capabilities by using VMs as their execution abstraction, offering superior compatibility over process-based TEEs like Intel SGX. The rising demand for Confidential VMs has spurred innovations from major chip manufacturers, such as AMD SEV, Intel TDX, and Arm CCA, and their integration into leading cloud platforms, including AWS, Azure, and Google Cloud. On the RISC-V platform, however, existing TEE architectures rely on process-level abstractions or custom hardware, leading to limited compatibility and scalability.This paper presents ZION, a confidential VM architecture for commodity RISC-V hardware that operates without custom extensions. ZION ensures security, flexibility, and efficiency through a short-path CVM mode and a secure vCPU mechanism for protecting and efficiently updating vCPU states, enhancing context-switching performance. It combines Physical Memory Protection (PMP) with paging for scalable memory isolation, employs a hierarchical memory structure for efficient management, and introduces a split-page-table-based mechanism for secure memory sharing with virtio devices. Evaluations show ZION achieves under 5% overhead in real-world applications, demonstrating its practicality.