Please correct me if I am wrong.
I looked through the code, it is not doing any form of hooking of system calls into the GPU to be directly called without it being known. What it does do is call out to the GPU to xor specific strings into a buffer stores on the GPU to hide it's log file. As far as I can tell, the syscall[x].syscall_func is simply a pointer to a GPU function to call which only has access to GPU memory. this is why in each of the "hooked" functions it has to transfer the data to be handled into the GPU. I don't see anything where direct memory access of the CPU is occurring by the GPU without there being a transfer from CPU to GPU.