You don't do it in UNIX because UNIX is fundamentally broken. That's the point. You do it through specialist software that works around the various problems. A common approach (i.e. compromise) in high-assurance security was to split systems between an untrusted, UNIX VM and critical components running directly on a microkernel/hypervisor. The kernels themselves were built as robust as possible sometimes with every potential, control or error state known. The apps outside VM's often used Ada or Java runtimes whose assurance and features were customized for apps needs. Robust middleware handled mediation and sometimes recovery. Many systems like this survived strong pentesting and worked without reported failures the field (or only failed-safe).

Then, there's the shit most people are doing and that Bryan advocates with UNIX. I also called him out on it listing numerous counters... with references backing them... to his comment at vezzy-fnord above.

https://news.ycombinator.com/item?id=10325607

Secure UNIX had already been tried by geniuses for a decade or two with always same results: architecture, language, and TCB were inherently so complex and insecure that even smallest versions had many 0-days and dozens of covert channels. He didn't respond, likely since he uses assertions instead of evidence. And all published evidence that I've ever seen contradicts his view of UNIX model superiority in robustness of any kind, sometimes performance.

Now, he's making all kinds of assertions about unikernels, deliberately avoiding evidence on some (eg performance), praising UNIX model/tech, and ignoring faults in his own approach. Should we take his word this time given prior result? Definitely not.