[constantcrying]

If it requires physical access an attacker can also attack the analog systems which are controlled by the software.

>I wish that vehicular systems all had air-gap level separation of messages, rendering it physically impossible to disrupt messages to critical systems like flight controls.

This is just false. There is nothing in the world which makes physically separating two airplane systems impossible.

>Can we really live with avionics platforms as a setting for the same kind of perpetual arms race against attackers that we have for general operating systems?

The comparison is false. OSs are exposed to the entire world. Airplane systems require physical access.

[contingencies]

Airplane systems require physical access.

... to potentially only one of the components within the system, at any point in its lifetime, across the entire supply chain and all build, test/verify, operations and maintenance processes.

(Edit in reply to child: Yes, obviously "the components within the system" means those actually connected, not a number 3 sprocket in seat 63E's incline mechanism. You have re-iterated my point.)

[constantcrying]

False. Most components are not connected to any of the relevant busses.

And if you had control over the specific component you need the plane is already compromised, whether the bus is open to spoofing or not is an irrelevant question.