Data diodes exist and have been used in high security or other risky cases when one circuit or bus absolutely has to be isolated except for one way communication.

In practice it's not typically necessary to go quite that far if a trusted communication processor is able to pass messages or set registers but only ever takes logic control flow input from the "safe" side. Plenty of equipment that wants to broadcast state over radio but never accepts any sort of input back beyond acks or whatever has done this for a long time.