From [the slides](https://pdos.csail.mit.edu/papers/vxa:fast05-slides.pdf https://pdos.csail.mit.edu/papers/vxa:fast05-slides.pdf) it sounds like what they do i

From [the slides](https://pdos.csail.mit.edu/papers/vxa:fast05-slides.pdf https://pdos.csail.mit.edu/papers/vxa:fast05-slides.pdf) it sounds like what they do is rewrite the code so syscall call into the vx32 runtime library instead and this prevents all syscalls except for the small handful they support. That in addition to memory sandboxing. So it doesn't really just run any random untrusted code, it has to be prepared to work with their sandboxing. The main purpose of this is being a self extracting archive not running untrusted code.