A Secure and Formally Verified Linux KVM Hypervisor

Abstract

Commodity hypervisors are widely deployed to support virtual machines (VMs) on multiprocessor hardware. Their growing complexity poses a security risk. To enable formal verification overssuch a large codebase, we introduce microverification, a new approach that decomposes a commodity hypervisor into a small core and a set of untrusted services so that we can prove security properties of the entire hypervisor by verifying the core alone. To verify the multiprocessor hypervisor core, we introduce security-preserving layers to modularize the proof without hiding information leakage so we can prove each layer of the implementation refines its specification, and the top layer specification is refined by all layers of the core implementation.To verify commodity hypervisor features that require dynamically changing information flow, we introduce data oracles to mask intentional information flow.We can then prove noninterference at the top layer specification and guarantee the resulting security properties hold for the entire hypervisor implementation. Using microverification, we retrofitted the LinuxKVMhypervisor with only modest modificationsto its codebase. Using Coq, we proved that the hypervisor protects the confidentiality and integrity of VM data, while retaining KVM’s functionality and performance. Our work is the first machine checked security proof for a commodity multiprocessor hypervisor.

BIO

Shih-Wei Li is a Ph.D. candidate in computer science at Columbia University advised by Professor Jason Nieh. His research interests span across areas in systems security, virtualization, verification, and performance evaluation. Li earned his B.S. from National Chiao Tung University and M.S. from National Tsing Hua University, both in computer science.