Sure there is: add this to the CPDLC standard and make all of the hardware modifications needed to support it:
Message type: Revert flight plan and lock
Message arguments: TIME: the time of the flight plan to use
Message description: Revert to the flight plan that was active at TIME that had been approved by both ground control and the pilot; engage autopilot; and disable all pilot / copilot access to all systems. If there is no approved flight plan then the flight plan is to return to the nearest suitable airport in the most direct route possible.
Additional modifications: Make sure that the pilot can never disable datalink communications with ground by any means that ground wouldn't have time to respond to.
Result: Nobody is ever "remote controlling" the plane from the ground. A murderous / terrorist ground controller can't crash the plane, only make it autopilot itself on a previously approved or otherwise reasonable flight plan. A pilot behaving suspiciously can't crash the plane, as ground control will just engage the autopilot and lock them out. To abuse the system both ground and the pilot would have to agree on a suicidal flight plan.