The type of kernel is orthogonal to this particular design flaw from what I
know. It's about how page tables are set up for user mode processes. I may
be wrong but pretty much every Unix or Unix-like kernel (including Plan 9)
follows the page table model Windows and Linux use: the ring 0 PTEs are
present in the page table, even in user mode, and we count on the
architecture to prevent ring 3 access to ring 0 memory. This is certainly
the case on all the ones I've worked on.
I don't think a microkernel would save you.
This is not a much ado about nothing case: it's early days and people can
make it work:
https://twitter.com/brainsmoke/status/948561799875502080