Identification and Evaluation of Sharing Memory Covert Timing Channel in Xen Virtual Machines

Abstract

Virtualization technology is the basis of cloud computing, and the most important property of virtualization is isolation. Isolation guarantees security between virtual machines. However, covert channel breaks the isolation and leaks sensitive message covertly. In this paper, we formally model the isolation into noninterference, and define that all the transmission channels violating noninterference are covert channels. With this definition, we present an identification method based on information flow. This method first compiles the source code into a more structured equivalent code with LLVM. And then a search algorithm is proposed to obtain the shared resources and the operational processes in the equivalent code. A new covert channel termed sharing memory covert timing channel (SMCTC) is identified from Xen source code. We construct channel scenario for SMCTC, and evaluate its threat with the metrics of channel capacity and transmission accuracy. The results show that SMCTC is much more threatened than CPU load based and cache based covert channels etc.