Re: [PATCH 9/9] sandbox: tpm: Support extending a PCR multiple times

[Simon Glass <sjg@chromium.org>]

Hi Ilias,

On Thu, 15 Jul 2021 at 13:21, Ilias Apalodimas
<ilias.apalodimas@linaro.org> wrote:
>
> On Thu, 15 Jul 2021 at 22:04, Ilias Apalodimas
> <ilias.apalodimas@linaro.org> wrote:
> >
> > On Mon, Jul 05, 2021 at 09:48:49AM -0600, Simon Glass wrote:
> > > It is fairly easy to handle this case and it makes the emulator more
> > > useful, since PCRs are commonly extended several times.
> > >
> > > Add support for this, using U-Boot's sha256 support.
> > >
> > > Signed-off-by: Simon Glass <sjg@chromium.org>
> > > ---
> > >
> > >  drivers/tpm/tpm2_tis_sandbox.c | 19 ++++++++++++-------
> > >  1 file changed, 12 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/drivers/tpm/tpm2_tis_sandbox.c b/drivers/tpm/tpm2_tis_sandbox.c
> > > index ed9c9a0bc9f..e84bcc7c4c8 100644
> > > --- a/drivers/tpm/tpm2_tis_sandbox.c
> > > +++ b/drivers/tpm/tpm2_tis_sandbox.c
> > > @@ -11,6 +11,7 @@
> > >  #include <asm/unaligned.h>
> > >  #include <linux/bitops.h>
> > >  #include <u-boot/crc.h>
> > > +#include <u-boot/sha256.h>
> > >  #include "sandbox_common.h"
> > >
> > >  /* Hierarchies */
> > > @@ -407,15 +408,19 @@ static int sandbox_tpm2_extend(struct udevice *dev, int pcr_index,
> > >                              const u8 *extension)
> > >  {
> > >       struct sandbox_tpm2 *tpm = dev_get_priv(dev);
> > > -     int i;
> > >
> > > -     /* Only simulate the first extensions from all '0' with only '0' */
> > > -     for (i = 0; i < TPM2_DIGEST_LEN; i++)
> > > -             if (tpm->pcr[pcr_index][i] || extension[i])
> > > -                     return TPM2_RC_FAILURE;
> > > +     if (!pcr_index) {
> > > +             memcpy(tpm->pcr[pcr_index], sandbox_extended_once_pcr,
> > > +                    TPM2_DIGEST_LEN);
> >
> > Why do we have to treat pcr 0 specially?
> > Can't we just get rid of sandbox_extended_once_pcr and just extend all the
> > PCRs with the value wee get?
> >
>
> Also looking at the entire series, SANDBOX_TPM_PCR_NB doesn't seem to change.
> I don't know too much about the tpm sandbox, but that effectively
> limits us to a single PCR?

I did send an updated series.

That's right, only one PCR is currently used by the tests.

Regards,
Simon