linux-kernel - Re: [PATCH v7 07/10] tmp, tmp_tis: Implement usage counter for locality

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Date:   Mon, 11 Jul 2022 23:15:49 +0200
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     Jason Andryuk <jandryuk@...il.com>
Cc:     Peter Huewe <peterhuewe@....de>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        linux@...ewoehner.de, linux-integrity@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>,
        l.sanfilippo@...bus.com, lukas@...ner.de, p.rosenberger@...bus.com
Subject: Re: [PATCH v7 07/10] tmp, tmp_tis: Implement usage counter for
 locality

Hi,

On 11.07.22 21:39, Jason Andryuk wrote:
> Hi,
>
> This patch subject has a typo "tmp, tmp_tis" -> "tpm, tpm_tis"
>

Right, thanks for the hint!

> On Wed, Jun 29, 2022 at 7:28 PM Lino Sanfilippo <LinoSanfilippo@....de> wrote:
>>
>> From: Lino Sanfilippo <l.sanfilippo@...bus.com>
>>
>> Implement a usage counter for the (default) locality used by the TPM TIS
>> driver:
>> Request the locality from the TPM if it has not been claimed yet, otherwise
>> only increment the counter. Also release the locality if the counter is 0
>> otherwise only decrement the counter. Ensure thread-safety by protecting
>> the counter with a mutex.
>>
>> This allows to request and release the locality from a thread and the
>> interrupt handler at the same time without the danger to interfere with
>> each other.
>>
>> By doing this refactor the names of the amended functions to use the proper
>> prefix.
>>
>> Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
>> Tested-by: Michael Niewöhner <linux@...ewoehner.de>
>> ---
>>  drivers/char/tpm/tpm_tis_core.c | 75 ++++++++++++++++++++++-----------
>>  drivers/char/tpm/tpm_tis_core.h |  2 +
>>  2 files changed, 53 insertions(+), 24 deletions(-)
>>
>> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
>> index bd4eeb0b2192..e50a2c78de9f 100644
>> --- a/drivers/char/tpm/tpm_tis_core.c
>> +++ b/drivers/char/tpm/tpm_tis_core.c
>
>> @@ -215,6 +226,20 @@ static int request_locality(struct tpm_chip *chip, int l)
>>         return -1;
>>  }
>>
>> +static int tpm_tis_request_locality(struct tpm_chip *chip, int l)
>> +{
>> +       struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
>> +       int ret = 0;
>> +
>> +       mutex_lock(&priv->locality_count_mutex);
>> +       if (priv->locality_count == 0)
>> +               ret = tpm_tis_request_locality_locked(chip, l);
>> +       if (!ret)
>> +               priv->locality_count++;
>> +       mutex_unlock(&priv->locality_count_mutex);
>> +       return ret;
>> +}
>> +
>
> This function should check that the requested locality matches the
> current locality otherwise this sequence would seemingly succeed
> though locality 0 is the one acquired.
>
> tpm_tis_request_locality(chip, 0);
> tpm_tis_request_locality(chip, 1);

This should not really be an issue since the TPM TIS driver only uses
locality 0.

>
> Regards,
> Jason

Regards,
Lino