Architecture support for guest-transparent VM protection from untrusted hypervisor and physical attacks

Abstract

The privacy and integrity of tenant's data highly rely on the infrastructure of multi-tenant cloud being secure. However, with both hardware and software being controlled by potentially curious or even malicious cloud operators, it is no surprise to see frequent reports of data leakages or abuses in cloud. Unfortunately, most prior solutions require intrusive changes to the cloud platform and none can protect a VM against adversaries controlling the physical machine. This paper analyzes the challenges of transparent VM protection against sophisticated adversaries controlling the whole software and hardware stack. Based on the analysis, this paper proposes HyperCoffer, a hardware-software framework that guards the privacy and integrity of tenant's VMs. HyperCoffer only trusts the processor chip and makes no security assumption on external memory and devices. Hyper-Coffer extends existing processor virtualization with memory encryption and integrity checking to secure data communication with off-chip memory. Unlike prior hardware-based approaches, HyperCoffer retains transparency with existing virtual machines (i.e., operating systems) and requires very few changes to the (untrusted) hypervisor. HyperCoffer introduces a mechanism called VM-Shim that runs in-between a guest VM and the hypervisor. Each VM-Shim instance for a VM runs in a separate protected context and only declassifies necessary information designated by the VM to the hypervisor and external environments (e.g., through NICs). We have implemented a prototype of HyperCoffer in a QEMU-based full-system emulator and the VM-Shim mechanism in a real machine. Performance measurement using trace-based simulation and on a real hardware platform shows that the performance overhead is small (ranging from 0.6% to 13.9% on simulated platform and 0.3% to 6.8% on real hardware for the VM-Shim mechanism).