[SeaBIOS] SeaBIOS Digest, Vol 72, Issue 33

[Stefan Berger]

"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.
 
> 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. 

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.

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()
   }
}

tpm_xyz() { [...] }

tpm12_bar() { [...] }

tpm2_bar() { [...] }

[...]

That's what I did before...

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

   Stefan


> 
> -Kevin
> 


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