It's pretty tricky to build a machine code validator to only be able to write and execute on certain areas... in x86, you have to take care of 'jumping in the m

It's pretty tricky to build a machine code validator to only be able to write and execute on certain areas... in x86, you have to take care of 'jumping in the middle of an instruction', that not only writes but also jumps are limited to your small area (because otherwise you will end up with something similar to ROP), etc.. I think Google Native Client did something like this, but it doesn't seem trivial. On the other hand, a way to bypass it could be that, when you detect one of those "executable code packets" has to be run, you undo all the injection/hooks in the game (so that you are really running a 100% unmodified process), and let the executable code packet run. After it finishes (you could detect this by a timer, page fault, etc. which can be handled by a different process in a different address space), you inject all the hooks again.