Comment by fc417fc802
3 hours ago
Aren't all of them microcoded? Some years back root was achieved on a line of intel processors and new instructions implemented as proof of concept. There's an academic paper, citation not immediately to hand.
3 hours ago
Aren't all of them microcoded? Some years back root was achieved on a line of intel processors and new instructions implemented as proof of concept. There's an academic paper, citation not immediately to hand.
Some instructions are microcoded but others take the fast path and avoid the microcode sequencer. Can't patch the latter in microcode RAM.
I saw the paper from Google last year and thought something in it aligned with not everything running through the microcode engine, though I could be wrong.
Might well be the case. I don't think I'm familiar with the paper you're referring to; any chance of at least a vague description?
Can’t find the pdf, but it’s all related to the zentool stuff:
https://github.com/google/security-research/blob/master/pocs...
Tavis spells it out there pretty quickly:
“ The simplest instructions (add, sub, mov, etc) are all implemented in hardware. The more complicated instructions like rdrand, fpatan and cmpxchg are microcoded. You can think of them as a bit like calling into a library of functions written in that RISC-like code.”