No, AMD64 does not ignore the upper 16 bits. They need to all equal the bit 47, otherwise the hardware raises a general protection fault (as opposed to a page f

No, AMD64 does not ignore the upper 16 bits. They need to all equal the bit 47, otherwise the hardware raises a general protection fault (as opposed to a page fault for accesses to unmapped pages). The problems mentioned in that article result from software that thinks this limit is set in stone. Such software encodes data in these upper bits, and then later masks it away before accessing the pointer.