MirageOS is a library operating system with which you can create a unikernel for the sole purpose of acting as Qubes OS’s firewall. In this post, I will walk you through how to set this up.

Advantages

• Small attack surface. The unikernel only contains a minimal set of libraries to function, so it has a much smaller attack surface than a general purpose operating system like a Linux distribution or openBSD.
• Low resource consumption. You only need about 64MB of RAM for each instance of the Mirage Firewall.
• Fast startup time.

Disadvantages

• No official package for Qubes OS. This means that you need to follow the development process on GitHub and download the new build whenever there is a release.
• Does not work well with the Windows PV network driver. With that being said, the Windows PV networking driver is pretty buggy on its own, and I don’t recommend that you use it anyways.

Installing the unikernel

To deploy MirageOS, you need to copy the vmlinuz and initramfs files from their releases page to /var/lib/qubes/vm-kernels/mirage-firewall in dom0.

TemplateVM

Create a TemplateVM:

qvm-create \
  --property kernel=mirage-firewall \
  --property kernelopts='' \
  --property memory=64 \
  --property maxmem=64 \
  --property vcpus=1 \
  --property virt_mode=pvh \
  --label=black \
  --class TemplateVM \
  your_template_name

Don’t worry if the TemplateVM doesn’t launch — we don’t need it to.

Disposable Template

Next, create a disposable template based on the TemplateVM you have just created.

qvm-create \
  --property template=your_template_name \
  --property provides_network=True \
  --property template_for_dispvms=True \
  --label=orange \
  --class AppVM \
  your_disposable_template_name

qvm-features your_disposable_template_name qubes-firewall 1
qvm-features your_disposable_template_name no-default-kernelopts 1

Your disposable templates should now launch and shut down properly.

Disposable FirewallVMs

You can now create disposable FirewallVMs based on your disposable template. I recommend replacing sys-firewall with a disposable Mirage firewall. If you use ProxyVMs like sys-whonix, I recommend that you add a disposable Mirage Firewall after the ProxyVM as well, and use it as the net qube for your AppVMs.

qvm-create \
  --property template=your_disposable_template_name \
  --property provides_network=True \
  --property netvm=your_net_qube_name \
  --label=orange \
  --class DispVM \
  your_firwall_name