privsec.dev/content/posts/qubes/Firewalling with MirageOS on Qubes OS.md

title	date	tags	author
Firewalling with MirageOS on Qubes OS	2022-08-26	Operating Systems MirageOS Qubes OS Security	Tommy

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 and while Qubes Mirage Firewall is still maintained, it rarely gets an official release. This means that you need to follow the development process on GitHub and make a new build yourself whenever there is a new commit.
• 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.

Prebuilt Image

You can obtain a prebuilt image of MirageOS here. I do follow the development of Qubes Mirage Firewall (since I use it on my personal computer) and will be uploading builds frequently.

Building Mirage-Firewall Yourself

First, you need an AppVm/DispVM with Docker installed to build the Mirage kernel. Fedora works well enough for this purpose.

Once you have an AppVM/DispVM to build it in, run the following commands:

git clone https://github.com/palainp/qubes-mirage-firewall/
cd qubes-mirage-firewall
git checkout mirage4
sudo ./build-with-docker.sh

Once the build process finishes, the unikernel should be at ~/qubes-mirage-firewall/_build/mirage-firewall/vmlinuz.

Deploy

First, you need to copy the unikernel to /var/lib/qubes/vm-kernels/mirage-firewall in dom0 and create a dummy initramfs:

mkdir -p /var/lib/qubes/vm-kernels/mirage-firewall/
cd /var/lib/qubes/vm-kernels/mirage-firewall/
qvm-run -p your_appvm_name 'cat /path/to/the/vmlinuz/file' > vmlinuz
gzip -n9 < /dev/null > initramfs

TemplateVM

Create a TemplateVM:

qvm-create \
  --property kernel=mirage-firewall \
  --property kernelopts='' \
  --property memory=128 \
  --property maxmem=128 \
  --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 shutdown 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