Secure Desktops with Qubes: Compartmentalization

This is the third article in my series about Qubes. In the first two articles, I gave an overview about what Qubes is and described how to install it. One of the defining security features of Qubes is how it lets you compartmentalize your different desktop activities into separate VMs. The idea behind security by compartmentalization is that if one of your VMs is compromised, the damage is limited to just that VM.

When you first start using Qubes, you may not be quite sure how best to divide up all of your files and activities into separate VMs. I know when I first started using it, I found inspiration in Joanna Rutkowska's (Qubes' creator) paper on how she used Qubes. In this article, I describe how I organize my activities into VMs on my personal computer. Although I'm not saying my approach is perfect, and I certainly could secure things even further than I do, I at least will provide you one example you can use to get started.

Summary of Qubes Concepts

In my previous article, I elaborated on overall Qubes concepts like the different VM types, trust levels and other features, but since I refer to those concepts in this article as well, here's a brief summary. (If you want to know more, read my column in the April and May 2016 issues.)

The first concept to understand with Qubes is that it groups VMs into different categories based on their use. Here are the main categories of VMs I refer to in the rest of the article:

  • Disposable VM: these also are referred to as dispVMs and are designed for one-time use. All data in them is erased when the application is closed.

  • Domain VM: these also often are referred to as appVMs. They are the VMs where most applications are run and where users spend most of their time.

  • Service VM: service VMs are split into subcategories of netVMs and proxyVMs. These VMs typically run in the background and provide your appVMs with services (usually network access).

  • Template VM: other VMs get their root filesystem template from a Template VM, and once you shut the appVM off, any changes you may have made to that root filesystem are erased (only changes in /rw, /usr/local and /home persist). Generally, Template VMs are left powered off unless you are installing or updating software.

When you create new VMs of any type, you can assign them a color based on your level of trust on a continuum from red (untrusted) to orange and yellow to green (somewhat more trusted) to blue and purple and grey (even more trusted) to black (ultimately trusted). The window borders and icons for a particular VM are colorized based on their trust level, so you get visual cues that help prevent you from, for instance, pasting trusted passwords into an untrusted VM.

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Kyle Rankin is a VP of engineering operations at Final, Inc., the author of a number of books including DevOps Troubleshooting and The Official Ubuntu Server Book, and is a columnist for Linux Journal. Follow him @kylerankin.