It doesn't, it just loses your session
That counts especially for accidental bugs and denial of service. To make a userland bug exploited adversarially not impact the rest of the system requires more hardening of the kernel.
Say it with me - there's no practical difference.
You can compartmentalise further.
Modern processors even give you these 'rings' to help with the hardware side of that, if you want to.
They differ in how easy a fix is to develop and roll out, and what the blast radius is.