I got you, bro:

The hardware DRAM controller maps "physical addresses" approximately to: {DRAM slot number, chip number in slot, bank number in chip, row number in bank, byte number in row} via a complex map for various irrelevant reasons. All permission checks are before this mapping. So if you change the mapping, you can access shit you should not be unable to, like TPM and SMM memory. OP found a way to change the mapping.