Earlier I was sent a link to a paper called "FlexOS: Towards Flexible OS Isolation"[1]. I thought the paper was great and subscribers to this list might be interested in it and what I thought about it. Like Spectrum, FlexOS is an operating system focused on compartmentalization, but it takes a very different approach. It's a library operating system (LibOS, also known as a unikernel). These operating systems are linked with a single program, and produce an operating system that only runs that single program. This can make for very efficient VMs. As a result, FlexOS isn't about isolation between programs, like Spectrum is, but instead tries to introduce isolation within a single program, generally at library boundaries. Therefore, Spectrum and FlexOS are highly complementary. FlexOS can use several different isolation strategies, including running different libraries in different VMs. Naturally there's a big performance overhead to this but amazingly, it seems like it can be on par with running the program normally on Linux, because the baseline performance is so much faster running on a unikernel than on Linux (not even in a VM AFAICT). Of a SQLite benchmark, the paper says: "Somewhat surprisingly, FlexOS with EPT2 [libraries in different VMs] performs almost identically to Linux. This is because the syscall latency is almost identical to the EPT2 gate latency on this system". Another inspired part of this paper is "Exploration with Partial Safety Ordering". I don't want to go into too much detail about this because the paper does such a good job of explaining it, but essentially you can give FlexOS a performance budget and a benchmark, and it will identify for you five or so of the best security configurations that meet your performance needs, across different combinations of isolation primitive, software hardening, etc. The biggest limitation I can see to FlexOS is that it is based on C source code transformations. Programs need to be specifically ported to it (although it seems like porting an individual program isn't too hard as long as it has good test coverage), and I don't know how easy it would be to integrate with another language. But it's definitely something to keep an eye on that could be useful if we ever find ourselves with a big C program doing important work in Spectrum. The use cases presented in the paper are quite compelling, especially the one about isolating exploitable libraries. And unikernels more generally are definitely worth keeping in mind if the performance results in this paper are anything to go by, although A Linux in Unikernel Clothing[2] is an interesting counterpoint. Finally, reminder that I collect interesting papers, blog posts, talks etc. in the Spectrum bibliography[3], where I've just added a link to this paper. If you come across interesting stuff like this that might be relevant to my work, please send it my way! [1]: https://arxiv.org/abs/2112.06566 [2]: https://doi.org/10.1145/3342195.3387526 [3]: https://spectrum-os.org/bibliography.html