[U-Boot] [RFC] SPL -> U-Boot Chain of Trust

[Andreas Dannenberg]

On Mon, Mar 28, 2016 at 03:32:40PM -0400, Tom Rini wrote:
> I'm interested in getting secure device support going, but it seems
> like we should need more than that, ie something to keep the chain of
> trust going.

Tom et al.,
I just saw your reply to Vitaly's email and I'm actually just looking
into something along the lines you brought up but I didn't want to
hijack that discussion so here's a new thread.

As for the chain of trust for ARMv7, my understanding is that when
using a combination of SPL and U-Boot there will always be a vendor-
specific initial boot (ROM) code that authenticates SPL, and then there
will need to be some code inserted into SPL that authenticates U-Boot
after it's loaded (for example by using some secure ROM API call and
such).

So I was looking into if there is already some generic framework for
this in U-Boot but didn't see anything obvious. One "easy" way would be
to add a simple call to an authentication routine to board_init_r
(u-boot/common/spl/spl.c) but let's say we add such a call for TI or
other vendor's stuff I suppose this would not scale very well.

But what about adding one generic call to a default authentication
function declared as __weak for spl_image that doesn't do anything, but
can be overwritten in vendor-specific files to provide means of
authenticating spl_image. Would this be a good approach?



Beyond that I was reviewing some of the awesome work from the Chromium
team and I think on ARMv7 after we get MLO to authenticate U-Boot
everything beyond that is already looking very solid and thorough (with
FIT, DTB/Kernel and initramfs authentication).


Thanks and Regards,

--
Andreas Dannenberg
Texas Instruments Inc