Re: [PATCH 0/5] RFC: Mezzanine handling for 96boards

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On Tue, Jun 26, 2018 at 10:19 AM Ard Biesheuvel
<ard.biesheuvel@xxxxxxxxxx> wrote:
> On 26 June 2018 at 10:09, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote:
> > On Mon, Jun 18, 2018 at 3:22 PM Ard Biesheuvel
> > <ard.biesheuvel@xxxxxxxxxx> wrote:
> >
> >> We should also consider firmware use of the mezzanines. For instance,
> >> the Secure96 has a RNG which UEFI may want to use so the early boot
> >> code can access is for KASLR. It also has a TPM, which should not be
> >> reset/reinitialized/etc by the OS if we want to make meaningful use of
> >> it.
> >
> > This problem: sharing or dedicating a piece of hardware to UEFI or
> > the TrustZone secure world is a generic problem not related to
> > mezzanines or plug-in boards specifically.
(...)
> I agree that this is *also* a problem. But it is not what I was talking about.
>
> My example is about peripherals that firmware and OS should both drive
> natively, and in the TPM case, the OS should be mindful of the fact
> that the measured state should be preserved.

Ah I see.

In that case this is something the TPM driver should be doing
I guess? I mean it is a "firmware plus OS TPM driver"-specific
problem.

I guess that would be hard to duct-tape on if the peripheral
is context-unaware and easy to do if the designer of the
peripheral HW took multiple call-context into account.
Whether TPM does this I don't know...

> Also, it means that we
> may be duplicating functionality between the OS and firmware [as
> usual] so it might make sense to come up with something that takes
> both use cases into account.

What we are doing now with Atmel's ECC chip is even worse:
duplicating functionality between OS and userspace. So I'm
trying to solve that first.

Yours,
Linus Walleij
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