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> The main thing is "Why undocumented?", not threat model and physical or remote exploit. No, the main thing is if VISA is for qualifying chips on the producti
by CodeWriter23 8y ago
> The main thing is "Why undocumented?", not threat model and physical or remote exploit.
No, the main thing is if VISA is for qualifying chips on the production line, why don’t they burn a fuse permanently disabling it on chips that pass QA?
- MrXOR 8y agoYet another main question, because ...
- smalley 8y agoVISA isn't for qualifying chips as much as it is for debugging chips including customer returns. Long ago access to limited versions of the signals was given to some customers under NDA and customers had the ability to set customer fuses which would prevent Intel from unlocking the debug features. There's also an unsupressable "debug enabled" bit hardwire to a lot of these functions if I remember so the parent system can always see if somebody turned on the debug functions. Turning on debug functions also usually had the effect of disabling/corrupting important key material. This said, its basically a giant signal mux system run into a main block, you'd be pretty limited on what preselected signals are available at a time. People were also reasonably careful not to give entire busses of signals at once.