[Skiboot] [PATCH] tpm_i2c_nuvoton: check TPM vendor id register during probe

[Oliver O'Halloran]

On Fri, Mar 6, 2020 at 8:17 AM Klaus Heinrich Kiwi
<klaus at linux.vnet.ibm.com> wrote:
>
>
>
> On 3/5/2020 3:54 PM, Eric Richter wrote:
> > +             /* ensure there's really the TPM we expect at that address */
> > +             if (tpm_i2c_request_send(tpm_device, SMBUS_READ, TPM_VID_DID,
> > +                                      1, &vendor, sizeof(vendor)) ||
> > +                 (vendor & TPM_VENDOR_ID_MASK) != TPM_650_VENDOR_ID) {
> if tpm_i2c_request_send() fails (negative error code), you skip this
> block and still tries to tpm_register_chip()?

Any non-zero value is considered true so it'll go down the error path
if the I2C transaction fails. I'm not 100% sure I understand what
you're saying here though...

> > +                     prlog(PR_ERR, "NUVOTON: i2c device inaccessible, or "
> > +                           "expected vendor id mismatch\n");
> > +                     if (vendor) {
> > +                             prlog(PR_ERR, "NUVOTON: expected 0x%X, "
> > +                                   "got 0x%X\n", TPM_650_VENDOR_ID, vendor);
> > +                     }
> > +                     free(tpm_device);
> > +                     continue;
> > +             }

> >               if (tpm_register_chip(node, tpm_device,
> >                                     &tpm_i2c_nuvoton_driver)) {
> >                       free(tpm_device);
> >
>
> Perhaps registering it would then fail? Since tpm_register_chip() sounds
> both like an action as well as a predicate, perhaps be more explicit
> about what we are testing? (I know this is outside the proposed patch
> but still...)

It doesn't fail, that's the problem. Right now we just keep trucking
along until skiboot tries to write a measurement to the TPM at which
point we notice it's not there.

>
>   -Klaus
>
> --
> Klaus Heinrich Kiwi <klaus at linux.vnet.ibm.com>
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