Systemd: RestrictAddressFamilies=none / SystemCallFilter=none
The man page says you can do:
to disallow all network families but I get an error for that
(at least in systemd 248)
But this works:
RestrictAddressFamilies=~AF_UNIX AF_NETLINK AF_INET AF_INET6 AF_PACKET
Similarly, I couldn't see a way to disable all system calls.
But then I read there are some that are always allowed.
So if you code that you only want that list:
That is the most restricted list possible.