linux-kernel - Re: [PATCH v4 1/6] tpm: dynamically allocate active

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Date:   Wed, 07 Nov 2018 06:10:30 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Nayna Jain <nayna@...ux.ibm.com>,
        Roberto Sassu <roberto.sassu@...wei.com>,
        jarkko.sakkinen@...ux.intel.com
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, silviu.vlasceanu@...wei.com
Subject: Re: [PATCH v4 1/6] tpm: dynamically allocate active_banks array

On Wed, 2018-11-07 at 11:44 +0530, Nayna Jain wrote:
> On 11/06/2018 08:31 PM, Roberto Sassu wrote:


> > @@ -878,11 +877,14 @@ static ssize_t tpm2_get_pcr_allocation(struct tpm_chip *chip)
> >   	if (rc)
> >   		goto out;
> >
> > -	count = be32_to_cpup(
> > +	chip->nr_active_banks = be32_to_cpup(
> >   		(__be32 *)&buf.data[TPM_HEADER_SIZE + 5]);
> 
> 
> As per my understanding, the count in the TPML_PCR_SELECTION represent 
> the number of possible banks and not the number of active banks.
> TCG Structures Spec for TPM 2.0 - Table 102 mentions this as explanation 
> of #TPM_RC_SIZE.

Instead of storing the result in a local variable, the only change
here is saving the result in the chip info (nr_active_banks).
 Everything else remains the same.


> >
> > -	if (count > ARRAY_SIZE(chip->active_banks)) {
> > -		rc = -ENODEV;
> > +	chip->active_banks = kmalloc_array(chip->nr_active_banks,
> > +					   sizeof(*chip->active_banks),
> > +					   GFP_KERNEL);

With this change, the exact number of banks can be allocated, as done
here.  Nice! 

Mimi

> > +	if (!chip->active_banks) {
> > +		rc = -ENOMEM;
> >   		goto out;
> >   	}
> >
>