Your processor has a lot of secret commands!
Neil Roy

This is a fascinating talk, not only on secret processor commands, some that are shared between different manufacturers, but not revealed to the public, but also some bugs on CPUs etc... great stuff!

video

Bruce Perry

I saw that too - and the friend I sent it to said he also had it in his Recommended. It's a bit scary, isn't it?

Neil Roy

Yeah. I especially wondered about the secret commands that were common on both AMD and Intel.

Bruce Perry

Some analysis might help to reveal how likely it is that those are emergent behaviour of the simplest way to interpret opcodes which they both chose to use, and how likely it is that they are the result of collaboration, espionage, common heritage or whatnot. Not something I have time for though :)

Chris Katko

video

Also a great talk. Hilarious guy.

bamccaig

I'm not a hardware expert at all, but it seems slightly conspiracy theorist-y to assume that anything that's undocumented on the machine is a useful instruction. I mean, certainly the VM bugs are concerning in their own right. But couldn't all of these millions of undocumented "instructions" just be garbage too? Might they be used maliciously? Probably. In that sense, they're certainly worth highlighting. I think it's a little bit of a leap to imply that the manufacturers are conspiring together, or that the government is involved, albeit, I wouldn't rule out of any of that. The thing is, ultimately, you always have to trust the processor. A sufficiently complex processor (perhaps of the near future) could attempt to detect these scans and alter its behavior...

Chris Katko

Except AMD and Intel (and others?) both implemented instructions that were undocumented and had the same affects. So they communicate with each other about instructions that they then don't tell consumers about.

bamccaig

Possibly, or maybe, Intel and AMD came to such similar chip designs that the remaining undocumented/undefined circuits happened to have identical (or at least, as far as reverse engineering tests revealed), identical solutions. I imagine that the chips are so complex at this point that the designs are far from optimal and they're just looking for anything that fits. But again, I don't know much about hardware. It's possible they conspired together, but what business reason would they have to do it? I can't imagine. And while I can imagine government bullying them to do it, that opens a pretty huge can of worms. If that's the truth it's time to throw our everyday lives away and take up arms in civil war.

Neil Roy

Also the guy in the video is a bit of an expert.

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