Black Hat
9 HN recommenders · recommended in 13 months, 2017–2022
44:29 · 381K views · Aug 31, 2017
Christopher Domas presents at Black Hat 2017 how page fault analysis and processor fuzzing can exhaustively search the x86 instruction set. The talk uncovers undocumented instructions and hardware bugs and shows limits of disassemblers.
HN recommends it as a clever, entertaining and easy-to-follow talk on finding hidden x86 instructions with the Sandsifter tool.
17 comments from Hacker News
I watched a super interesting Black Hat video on youtube that talked about discovering secret instructions on CPUs by iterating over each bit of opcodes until you get an illegal instruction, and thereby discovering if an opcode is valid or not. He set up a room full of PCs running his code and had hardware to auto-reset them when they crashed. this video
One of my favourite talks I watched was "Low Cost Non-Invasive Biomedical Imaging - An Open Electrical Impedance Tomography Project" [LINK] As it presented an interesting technique I'd never heard of before, along with an implementation. Also I thought the 'Breaking the x86 Instruction Set' talk was extremely clever - this video
> I trust its disassembler (especially for mainstream languages) more than almost any other disassembler Might I suggest Christopher Domas' Black Hat talk "Breaking the x86 ISA", along the way of which he demonstrates the limitations of all disassemblers out there, including IDA's :) Talk: this video Slides: [LINK] Paper: [LINK]
"I thought you were saying that the use of microcode would complicate verification of the hardware." I do think that microcode opens up the possibility of subtle injections to follow code/hardware paths you might not easily predict. A really good talk on reverse engineering an ISA implementation: this video
How about undocumented instructions? Sandsifter[1] is an interesting project and the video from BlackHat[2] is a good watch. There's also a previous discussion of it on HN[3]. [1] [LINK] [2] this video [3] [LINK]