UBC Theses and Dissertations

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UBC Theses and Dissertations

Breaking up is hard to do : security and functionality in a commodity hypervisor Nanavati, Mihir Sudarshan


Virtualization platforms have grown with an increasing demand for new technologies, with the modern enterprise-ready virtualization platform being a complex, feature-rich piece of software. Despite the small size of hypervisors, the trusted computing base (TCB) of most enterprise platforms is larger than that of most monolithic commodity operating systems. Several key components of the Xen platform reside in a special, highly-privileged virtual machine or the “Control VM”. We present Xoar, a modified version of the Xen platform that retrofits the modularity and isolation principles championed by microkernels onto a mature virtualization platform. Xoar divides the large, shared control VM of Xen’s TCB into a set of independent, isolated, single purpose components called shards. Shards improve security in several ways: components are restricted to the least privilege necessary for functioning and any sharing between guest VMs is explicitly configurable and auditable in tune with the desired risk exposure policies. Microrebooting components at configurable frequencies reduces the temporal attack surface. Our approach does not require any existing functionality to be sacrificed and allows components to be reused rather than rewritten from scratch. The low performance overhead leads us to believe that Xoar is viable alternative for deployment in enterprise environments.

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