tl;dr: x86 processors have an ancient feature (unused by now) that allows to move the memory window of the APIC registers to an arbitrary address. By moving thi

tl;dr: x86 processors have an ancient feature (unused by now) that allows to move the memory window of the APIC registers to an arbitrary address. By moving this window, it is possible to circumvent built-in hardware security checks and access the highly privileged System Management Mode (Ring -2) from Ring 0 Code.