[boznz]

Same could be said for MIPS or RISC-V or indeed any piece of silicon.

As an embedded designer I know for a fact that CPUs used in embedded systems get so much scrutiny on their I/O messages all the way up the stack, it would be real good subversion to hide something like this and not be discovered in all use case scenarios. More likely is some sort of back door when you can access the hardware. Disclaimer I only work on the smallest MIPS and ARM embedded chips not those with full MMU's