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According to Positive Technologies, on Skylake and higher (like the Purism machines) the kernel loads the BUP, and the HAP bit only disables the normal userspace processes [1].
What proof do you have that the kernel itself is halted?
[1] http://blog.ptsecurity.com/2017/08/disabling-intel-me.html
On 12/13/2017 11:34 AM, Youness Alaoui wrote:
I guess I still disagree with the use of the word "disabled". If the ME wasn't required for boot, and was actually disabled within a few cycles of its CPU starting, the remaining attack surface simply wouldn't exist. This is not what happens though, and AFAIK even the ME kernel continues to run since the ME needs to continue handling platform power events. If this many holes are present in even the ROM code, then having the ME kernel running remains a massive security problem.
I'm just going to answer the bit about the use of the term "disabled". I've explained it in my blog post before (here if you missed it : https://puri.sm/posts/deep-dive-into-intel-me-disablement/) but I do believe the ME is in this case Disabled. What you are thinking about is what I called "Removed". The reason it's called disabled is because the ME stops running, it's not actively doing anything, it doesn't respond to HECI, it doesn't even boot into the kernel. You said that "the ME kernel continues to run", but that's not the case. The entire ME core stops execution during the bring-up phase, so it's technically disabled because it stops itself at some point after boot. Having the ME *removed* would be interesting because that would mean that even the bring up phase wouldn't get executed and we could remove the entire ME firmware from the flash. But that still wouldn't mean that nothing runs on the ME core because there is still some small code embeded in the ROM. Anyways, that's my justification on why using the term "disabled" is valid in this case when HAP is enabled. You are free to disagree if that didn't convince you.
- -- Timothy Pearson Raptor Engineering +1 (415) 727-8645 (direct line) +1 (512) 690-0200 (switchboard) https://www.raptorengineering.com