At a theoretical level, it wouldn't be too difficult to write a C interpreter from scratch, with enough simple obfuscation that detecting what it is interpretin

At a theoretical level, it wouldn't be too difficult to write a C interpreter from scratch, with enough simple obfuscation that detecting what it is interpreting really would start looking like strong AI. And even if such a sophisticated program were written and somehow managed to not take up too much CPU time, it would at least probably result in rather large binary size increases in whatever it's injected into... even Linux isn't so big that a few hundred kilobytes wouldn't stick out like a sore thumb.