[SeaBIOS] SeaBIOS Digest, Vol 72, Issue 33

[Kevin O'Connor]

On Fri, Jan 08, 2016 at 12:19:52PM -0500, Stefan Berger wrote:
> "Kevin O'Connor" <kevin at koconnor.net> wrote on 01/08/2016 11:41:13 AM:
> > On Thu, Jan 07, 2016 at 03:39:13PM -0500, Stefan Berger wrote:
> > > "Kevin O'Connor" <kevin at koconnor.net> wrote on 01/07/2016 03:14:37 PM:
> > > > I don't have input on what TPM2 organization should look like, 
> mainly
> > > > because I don't know what TPM2 entails.  I gather the TIS commands 
> are
> > > > changing, but what else changes?  Does the ACPI log, BIOS interface,
> > > > or tpm menu change?  Do you have a pointer to the TPM2 spec (when I
> > > > last looked it seemed that TPM2 was still being worked on).
> > > 
> > > The TIS got more registers; some flags allow detection of the TPM 
> version.
> > > 
> > > All commands changed -- no backwards compatibility. The header 
> 'fields' 
> > > are the same, their ordinal and tag values are not.
> > > 
> > > Spec: 
> > > 
> http://www.trustedcomputinggroup.org/resources/tpm_library_specification
> > 
> > Thanks.  Does the hardware interface change as well (ie, is it still
> > the same reads/writes to MMIO at 0xfed40000)?
> >
> 
> It has the same address, but one or two more registers.

Does it require a different tpm_drivers.c implementation - with
something like tpmhw1_transmit() and tpmhw2_transmit() functions?

> > My initial thought would be to do what you've proposed - have wrapper
> > functions around the TPM commands (eg, tpm_extend, tpm_get_capability,
> > read_permanent_flags) and teach those functions how to send the two
> > different styles of commands (and translate the responses if
> > necessary).
> 
> So the good thing is that some of the code can be shared between 1.2 and 
> 2.0,
> to a certain 'depth' at least. An example of a shared function would be 
> this one.
> 
> static void
> tpm_add_event_separators(void)
> {
>     static const u8 evt_separator[] = {0xff,0xff,0xff,0xff};
>     u32 pcrIndex;
>     for (pcrIndex = 0; pcrIndex <= 7; pcrIndex++)
>         tpm_add_measurement_to_log(pcrIndex, EV_SEPARATOR,
>                                    NULL, 0,
>                                    evt_separator,
>                                    sizeof(evt_separator));
> }
> 
> Following this function further down:
> 
> tpm_add_measurement_to_log() [on current master] can be completely
> shared as well. tpm_log_extend_event would need to become a function that
> branches into tpm12_log_extend_event and tpm2_log_extend_event, depending
> on detected version of TPM. 

Sounds like a new tpm_extend() function could be made with just the
hardware command.  And then it could handle the v1 and v2 cases and
thus reduce the amount of duplicated code.

> tpm_log_event could again be shared since ACPI logging is the same.
> Same for tpm_fill_hash for as long as we only support sha1.
> 
> Basically all functions where commands are created cannot be shared.
> Also TPM 2's initialization is a bit different and it supports more
> hashes.

If the init is notable different maybe just do tpm1_startup() and
tpm2_startup()?

> So it actually speaks against splitting this up into different files, but 
> the
> outcome may be that the code would show a mix of tpm12_*, tpm2_*, and
> tpm_* functions in the format of
> 
> tpm12_foo() { [...] }
> 
> tpm2_foo() { [...] }
> 
> tpm_foo() {
>    switch (tpmversion) {
>    1.2:
>       return tpm12_foo()
>    2:
>       return tpm2_foo()
>    }
> }

Okay.  But, I would say that if both tpm12_foo() and tpm2_foo() are
both only a few lines that it might be better to just inline it all
into tpm_foo().  An 'if' might be more succinct also - hopefully there
isn't a tpm3 in the works..

> tpm_xyz() { [...] }
> 
> tpm12_bar() { [...] }
> 
> tpm2_bar() { [...] }
> 
> [...]
> 
> That's what I did before...

Oh, were there tpm2 patches available?  I must have missed them.

> If none of the code could be shared the decision to split it up completely 
> would be a lot easier.

Agreed.

-Kevin