On using QubesOS MirageOS firewall

So I'm lucky to attend the 4th MirageOS hack retreat in Marrakesh this week, where I learned to build and use qubes-mirage-firewall, which is a MirageOS based (system) firewall for Qubes OS. The main visible effect is that this unikernel only needs 32 megabytes of memory, while a Debian (or Fedora) based firewall systems needs half a gigabyte. It's also said to be more secure, but I have not verified that myself

In the spirit of avoiding overhead I decided not to build with docker as the qubes-mirage-firewall's README.md suggests, but rather use a base Debian stretch system. Here's how to build natively:

sudo apt install git opam aspcud curl debianutils m4 ncurses-dev perl pkg-config time

git clone https://github.com/talex5/qubes-mirage-firewall
cd qubes-mirage-firewall/
opam init
# the next line is super useful if there is bad internet connectivity but you happen to have access to a local mirror
# opam repo add local http://10.0.0.2:8080
opam switch 4.04.2
eval `opam config env`
## in there:
opam install -y vchan xen-gnt mirage-xen-ocaml mirage-xen-minios io-page mirage-xen mirage mirage-nat mirage-qubes netchannel
mirage configure -t xen
make depend
make tar

Then follow the instructions in the README.md and switch some AppVMs to it, and then make it the default and shutdown the old firewall, if you are happy with the results, which currently I'm not sure I am because it doesn't allow updating template VMs...

Update: qubes-mirage-firewall allows this. Just the crashed qubes-updates-proxy service in sys-net prevented it, but that's another bug elsewhere.

I also learned that it builds reproducibly given the same build path and ignoring the issue of timestamps in the generated tarball, IOW, the unikernel (and the 3 other files) inside the tarball is reproducible. And I still need to compare a docker build with a build done the above way & and I really don't like having to edit the firewalls rules.ml file and then rebuilding it. More on this in another post later, hopefully.

Oh, I didn't mention it and won't say more here, but this hack retreat and it's organisation is marvellous! Many thanks to everyone here!