There is a link to a full demo someone posted here [1].
They don't run the linux kernel at all. That /proc/cpuinfo is a part of a limited subset from what procfs usually offers. They enter their linux compatible "subsystem" via a bash binary, which could probably be any linux elf binary, since they run them unmodified. So, it looks like they actually implemented most of the syscalls with some of them emulating necessary parts of linux environment, like procfs.
They don't run the linux kernel at all. That /proc/cpuinfo is a part of a limited subset from what procfs usually offers. They enter their linux compatible "subsystem" via a bash binary, which could probably be any linux elf binary, since they run them unmodified. So, it looks like they actually implemented most of the syscalls with some of them emulating necessary parts of linux environment, like procfs.
[1] https://sec.ch9.ms/ch9/5db6/8ee786b7-9fc5-45bf-94d0-16ea9176...