On Improving the Security of Virtualized Systems through Unikernelized Driver Domain and Virtual Machine Monitor Compartmentalization and Specialization

Virtualization is the backbone of cloud infrastructures. Its core subsystems include hypervisors and virtual machine monitors (VMMs). They ensure the isolation and security of co-existent virtual machines (VMs) running on the same physical machine. Traditionally, driver domains -- isolated VMs in a hypervisor such as Xen that run device drivers -- use general-purpose full-featured OSs (e.g., Linux), which has a large attack surface, evident by the increasing number of their common vulnerabilities and exposures (CVEs). We argue for using the unikernel operating system (OS) model for driver domains. In this model, a single application is statically compiled together with the minimum necessary kernel code and libraries to produce a single address-space image, reducing code size by as much as one order of magnitude, which yields security benefits. We develop a driver domain OS, called Kite, using NetBSD OS's rumprun unikernel. Since rumprun is directly based on NetBSD's code, it allows us to leverage NetBSD's large collection of device drivers, including highly specialized ones such as Amazon ENA. Kite's design overcomes several significant challenges including Xen's limited para-virtualization (PV) I/O support in rumprun, lack of Xen backend drivers which prevents rumprun from being used as a driver domain OS, and NetBSD's lack of support for running driver domains in Xen. We instantiate Kite for the two most widely used I/O devices, storage and network, by designing and implementing the storage backend and network backend drivers. Our evaluations reveal that Kite achieves competitive performance to a Linux-based driver domain while using 10x fewer system calls, mitigates a set of CVEs, and retains all the benefits of unikernels including a reduced number of return-oriented programming (ROP) gadgets and advanced gadget-related metrics. General-purpose VMMs include a large number of components that may not be used in many VM configurations, resulting in a large attack surface. In addition, they lack intra-VMM isolation, which degrades security: vulnerabilities in one VMM component can be exploited to compromise other components or that of the host OS and other VMs (by privilege escalation). To mitigate these security challenges, we develop principles for VMM compartmentalization and specialization. We construct a prototype, called Redwood, embodying those principles. Redwood is built by extending Cloud Hypervisor and compartmentalizes thirteen critical components (i.e., virtual I/O devices) using Intel MPK, a hardware primitive available in Intel CPUs. Redwood has fifteen fine-grained modules, each representing a single feature, which increases its configurability and flexibility. Our evaluations reveal that Redwood is as performant as the baseline Cloud Hypervisor, has a 50% smaller VMM image size and 50% fewer ROP gadgets, and is resilient to an array of CVEs. I/O acceleration architectures, such as Data Plane Development Kit (DPDK) enhance VM performance by moving the data plane from the VMM to a separate userspace application. Since the VMM must share its VMs' sensitive information with accelerated applications, it can potentially degrade security. The dissertation's final contribution is the compartmentalization of a VM's sensitive data within an accelerated application using the Intel MPK hardware primitive. Our evaluations reveal that the technique does not cause any degradation in I/O performance and mitigates potential attacks and a class of CVEs.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Computer Engineering

Department dc:contributor.department

Electrical and Computer Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2023

Author dc:creator

• Mehrab, A. K. M. Fazla

Chair dc:contributor.committeechair

• Ravindran, Binoy

Committee members dc:contributor.committeemember

• Yao, Danfeng
• Zeng, Haibo
• Nikolaev, Ruslan
• Plassmann, Paul E.

• Operating Systems
• Unikernels
• Virtualization
• Hypervisors
• VMM
• Compartmentalization

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Dc Identifier Other

vt_gsexam:36667

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/114237