There is so many ways to implement backdoors in CPUs, even completely analog ones: https://hackaday.com/2017/04/25/an-analog-charge-pump-fabrication-time-attac

There is so many ways to implement backdoors in CPUs, even completely analog ones: https://hackaday.com/2017/04/25/an-analog-charge-pump-fabrication-time-attack-compromises-a-processor/ https://hackaday.com/2017/04/25/an-analog-charge-pump-fabric...