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A computer spends the vast majority of its time and memory in userspace, so this tradeoff isn't as bad as it sounds.

The benefit also isn’t as big as you might expect. Most of Linux’s recently found security vulnerabilities were due to ToC/ToU bugs. Fil-C would not magically fix these problems.

It would sometimes be a good trade off, for some users. But I don’t think many regular users would choose to pay this cost.

a fun exercise is to ask an LLM how it might be applied.

You can run your Fil–C userland on provably–secure seL4.

(Left as an exercise for the reader)

If you’re using SeL4, userland processes are already strictly sandboxed. There’s still some benefit to Fil-C, since the added memory safety would make it much more difficult to take over a process. But the blast radius of a compromised program in SeL4 is much smaller because of the capability model.

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