[coreboot] Is Goryachy's JTAG hack a chance for free firmware ?

Denis 'GNUtoo' Carikli GNUtoo at no-log.org
Tue Dec 12 17:32:28 CET 2017

On Wed, 29 Nov 2017 23:39:27 +0100
"Enrico Weigelt, metux IT consult" <info at metux.net> wrote:

> Hi folks,
> i'm curios whether Goryachy's JTAG hack is a chance for
> getting rid of all proprietary ME/UEFI firmware.
> If i'm correct, the ME firmware (or parts of it) is signed, and
> the CPU won't run (or switches off) if signatures don't match.
> Can the JTAG channel be used to get around that ?
We don't have enough information on that yet to understand if it's
possible or not.

More precisely, I don't know:
- If it's possible to halt the Management Engine (trough the JTAG)
  before it starts executing code, load code for it to execute, and
  make it execute that unsigned free software code that would
  initialize enough hardware to make the computer start.
- Or if it's possible to halt the Management Engine and instead
  initialize that hardware trough the JTAG.
- If it would be possible to use another computer and an USB3 controller
  that don't depend on non-free software to initialize a recent Intel
  system without depending on any non-free software.
  It would be nice to be able to use A Rockchip SBC with USB3, or an
  SBC with a free software bootloader and with a PCIe interface and a
  PCIe USB3 card to do that.
  If this is possible it would enable building a desktop or server
  computer that can start with free software. The SBC could also be
  used to run some tasks while the main computer is off, such as an IRC
  client or server software.
  However If getting JTAG trough DCI requires a skylake computer, then
  there is a chicken and egg problem...

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