MirageOS and my recent involvement

[Hannes Mehnert <hannes@xxxxxxxxxxx>]

Dear all,

it is pretty quite on this list. I'm not sure whether this is a good 
sign or not.
I unfortunately had to cancel the retreat in November due to lack of 
signups (3 people managed to sign up within the deadline) :/ While late 
signups are possible, it is always a burden.
But I have some exciting MirageOS related news that I find worth 
sharing, and hope to engage discussions by doing so. Maybe it is also 
worth to restart weekly / biweekly MirageOS meetings (as in the old 
days) -- what do you think?
Some repositories in the mirage organization are suffering from bitrot, 
and/or lack of cleanups or reviews (such as the ocaml-solo5 PR waiting 
since a long time for proper reviews that would enable to use OCaml 5) 
-- my personal experience with OCaml 5 from a resource perspective is 
not very good, that's why I don't really care about that too much (and 
am happy that 4.14 is under long-term support).
## MirageVPN / OpenVPN

We at robur managed to receive EU (NGI Assure) funding to work on 
MirageVPN (an OpenVPN implementation), which we started back in 2019 - 
to add more mdoern crypto and more recent features (tls-crypt, ..), a 
server implementation, a QubesOS client unikernel, ... -- 
https://nlnet.nl/project/MirageVPN/ \o/
The source is developed at https://github.com/robur-coop/miragevpn (also 
see our blog entries at https://blog.robur.coop)
In case you are using OpenVPN and are looking for a replacement, please 
have a try (and/or open issues if you're stuck / missing features).
## DNSvizor / DNSmasq

We at robur also managed to receive EU (NGI0 Entrust) funding to work on 
DNSvizor (a DNS resolver and DHCP server - basically a DNSmasq 
replacement) https://nlnet.nl/project/DNSvizor/ (earlier funding for 
this project didn't pan out due to how to direct the money -- 
https://nlnet.nl/project/Robur/) -- but we already have a basic 
repository up and running https://github.com/robur-coop/dnsvizor
At the earlier retreats previous versions of such a unikernel were 
actively being used - and we also discovered some issues that were then 
fixed on site. But now, finally putting several months of effort into it 
(in 2024) will hopefully result in a useful unikernel.
Again, if you wish for some features, or have a DNSmasq in production 
that you're keen on having replaced, don't hesitate to open an issue 
(and provide us with your configuration).
## uTCP

Since August I've motivated myself to work a bit more on uTCP, a TCP/IP 
stack that originated from Netsem, a formal model in HOL4.
Apart from minor bugfixes to get it compiling again, I pushed it into 
production (first for retreat.mirage.io, then once the resource leakage 
was sorted, also on a.ns.robur.coop, and now finally as tls reverse 
proxy on *.robur.coop).
Some highlights from the last months:
making it usable:
- properly set initial window
- segment reassembly

performance:
- improve performance of checksum computation by a factor of 5
- avoid lots of allocations (improved performance by factor of 3)

correctness
- drop connection in LAST ACK if FIN was received
- fix exceptions (Cstruct.shift exceeding send queue, Cstruct.shiftv 
with negative amount)
- no longer being stuck in various states (CLOSE WAIT, FIN WAIT 2) 
[which turned out to be an issue in the model]
- avoid usage of multiple maps

convenience:
- add metrics and monitoring
- since mirage 4.4.1, using uTCP is possible without too much headache 
(still some, see 
https://github.com/mirage/retreat.mirage.io/blob/748f29e20499a8b508b11a302e8890202202e854/config.ml#L36-L69 
for an example)
It is now in a nice shape - while working on it, I also discovered that 
mirage-tcpip has some issues (apart from resource leaks, it also doesn't 
validate any checksum). There are still some open issues to work on 
before releasing an initial version (such as path MTU discovery, 
selective acknowledgement, congestion control, increase initial window 
size, accurate byte counting). But the upside is that even the reverse 
TLS tunnel that carries quite some load doesn't seem to leak memory anymore.
repository: https://github.com/robur-coop/utcp
blog article:https://hannes.robur.coop/Posts/TCP-ns
network semantics: https://www.cl.cam.ac.uk/~pes20/Netsem/
JACM journal paper (2019): http://www.cl.cam.ac.uk/~pes20/Netsem/paper3.pdf

## NetHSM

The first (to my knowledge) commercial product using MirageOS (and Muen) 
is now for sale; it is a "Hardware Security Module", so something you 
can store your private keys which hopefully never get extracted. With 
the robur team (namely Steffi and Martin) I was involved in the early 
days (doing system design and implementation) [though I've not followed 
changes in later years]. See their announcement at 
https://www.nitrokey.com/news/2023/after-8-years-development-nethsm-10-available-first-open-source-hardware-security-module
NB: I don't agree with everything they say. I'm especially sad how they 
did a code dump on GitHub instead of preserving the commit history.

Best,

Hannes