I could be wrong, but I think this is what Memory Management Units are for, on processor chips. It's one major differentiator between application processors and more embedded ones like Cortex-M or ATMega MCUs, which typically can't run complex modern operating systems. A lot of those chips have a simpler Memory Protection Unit that does basic enforcement of permissions like read+execute, read+write, etc, but they lack the ability to partition memory virtually between a large number of potential 'owners.'
I think - I'm still learning about this embedded stuff.
The point is that once you're doing that, and implementing communication between all your separate owners (which map pretty precisely to a reasonable definition of "processes")... you've just implemented another operating system, not a unikernel.
I think - I'm still learning about this embedded stuff.