Re: [PATCH v2 1/5] tpm_tis: Fix check_locality for correct locality acquisition

[Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>]

On Thu, Oct 01, 2020 at 11:09:21AM -0700, James Bottomley wrote:
> The TPM TIS specification says the TPM signals the acquisition of
> locality when the TMP_ACCESS_REQUEST_USE bit goes to one *and* the
> TPM_ACCESS_REQUEST_USE bit goes to zero.  Currently we only check the

Put a reference to the section.

I'm *guessing* that the spec is

https://trustedcomputinggroup.org/resource/pc-client-work-group-pc-client-specific-tpm-interface-specification-tis

Please have this and also location in this spec.

> former not the latter, so check both.  Adding the check on
> TPM_ACCESS_REQUEST_USE should fix the case where the locality is
> re-requested before the TPM has released it.  In this case the
> locality may get released briefly before it is reacquired, which
> causes all sorts of problems. However, with the added check,
> TPM_ACCESS_REQUEST_USE should remain 1 until the second request for
> the locality is granted.

The description is really good and understandable otherwise.

For me it is not obvious at all, why this is missing a fixes
tag?

> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> 
> ---
> 
> v2: added this patch

Use the cover letter for the changelog. I'm afraid that I might
miss these otherwise.

> ---
>  drivers/char/tpm/tpm_tis_core.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index 92c51c6cfd1b..f3ecde8df47d 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -125,7 +125,8 @@ static bool check_locality(struct tpm_chip *chip, int l)
>  	if (rc < 0)
>  		return false;
>  
> -	if ((access & (TPM_ACCESS_ACTIVE_LOCALITY | TPM_ACCESS_VALID)) ==
> +	if ((access & (TPM_ACCESS_ACTIVE_LOCALITY | TPM_ACCESS_VALID
> +		       | TPM_ACCESS_REQUEST_USE)) ==
>  	    (TPM_ACCESS_ACTIVE_LOCALITY | TPM_ACCESS_VALID)) {
>  		priv->locality = l;
>  		return true;
> -- 
> 2.28.0
> 

/Jarkko