Hector Martin

I'm worried about scenario of "plug usb kit, hard reboot, implant". Once the OS is running, it's usually quite harder

There's more than one TAP accessible via DCI. Wouldn't be surprised if you could still take over w/o x86 JTAG.

But really the whole point is this should be disabled in PCH from boot.

It's trivial to check if you're vulnerable. Connect USB3 crossover cable to host, reboot. If it ever enumerates, vuln.

So you just need a crossover and it works? Nice... Do the debug serial port work that way?

There's USB Debug Class support but that's not DCI, that's a generic thing an OS can use.

Yes, but from what I understood it required a special adapter to connect to (it's mandated by MS to be present, though)

For USB debug class all you need is a crossover cable too, and support in the xHCI (intel hosts have it).