[Skiboot] [PATCH 3/3] libstb/tpm: block access to unknown i2c devs on the tpm bus

[Nayna]

On 12/3/19 12:46 AM, Oliver O'Halloran wrote:
> Our favourite TPM is capable of listening on multiple I2C bus addresses
> and although this feature is supposed to be disabled by default we have
> some systems in the wild where the TPM appears to be listening on these
> secondary addresses.
>
> The secondary addresses are also susceptible to the bus-lockup problem
> that we see with certain traffic patterns to the "main" TPM address.
> We don't know what addresses the TPM might be listening on it's best to
> take a conservitve approach and only allow traffic to I2C bus addresses
> that we are explicitly told about by firmware.
>
> This is only required on the TPM bus, so this patch extends the existing
> TPM workaround to also check that a DT node exists for any I2C bus
> address the OS wants to talk to. If there isn't one, we don't forward
> the I2C request to the bus and return an I2C timeout error to the OS.

I think the userspace will talk to kernel tpm driver, which in turn will 
talk to Physical TPM via skiboot i2c driver.

I don't think the userspace will ever reach the skiboot tpm driver.  I 
am wondering if the fix has to be handled in the skiboot core i2c driver 
rather than in tpm_i2c_nuvoton driver.

Am I missing something ?

Thanks & Regards,

       - Nayna