linux-kernel - Re: [PATCH] tpm: Add flag to use default cancellation policy

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Message-ID: <1a20cd56-cc6f-d1c3-2e9d-c6b1fe278959@linux.ibm.com>
Date:   Thu, 8 Sep 2022 08:53:14 -0500
From:   Eddie James <eajames@...ux.ibm.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        peterhuewe@....de, jarkko@...nel.or, jgg@...pe.ca, joel@....id.au,
        Alexander.Steffen@...ineon.com
Subject: Re: [PATCH] tpm: Add flag to use default cancellation policy


On 9/8/22 00:22, Jarkko Sakkinen wrote:
> On Wed, Sep 07, 2022 at 11:43:17AM -0500, Eddie James wrote:
>> The check for cancelled request depends on the VID of the chip, but
>> some chips share VID which shouldn't share their cancellation
>> behavior. This is the case for the Nuvoton NPCT75X, which should use
>> the default cancellation check, not the Winbond one.
>> To avoid changing the existing behavior, add a new flag to indicate
>> that the chip should use the default cancellation check and set it
>> for the I2C TPM2 TIS driver.
>>
>> Signed-off-by: Eddie James <eajames@...ux.ibm.com>
>> ---
>>   drivers/char/tpm/tpm_tis_core.c | 18 ++++++++++--------
>>   drivers/char/tpm/tpm_tis_core.h |  1 +
>>   drivers/char/tpm/tpm_tis_i2c.c  |  1 +
>>   3 files changed, 12 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
>> index 757623bacfd5..175e75337395 100644
>> --- a/drivers/char/tpm/tpm_tis_core.c
>> +++ b/drivers/char/tpm/tpm_tis_core.c
>> @@ -682,15 +682,17 @@ static bool tpm_tis_req_canceled(struct tpm_chip *chip, u8 status)
>>   {
>>   	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
>>   
>> -	switch (priv->manufacturer_id) {
>> -	case TPM_VID_WINBOND:
>> -		return ((status == TPM_STS_VALID) ||
>> -			(status == (TPM_STS_VALID | TPM_STS_COMMAND_READY)));
>> -	case TPM_VID_STM:
>> -		return (status == (TPM_STS_VALID | TPM_STS_COMMAND_READY));
>> -	default:
>> -		return (status == TPM_STS_COMMAND_READY);
>> +	if (!test_bit(TPM_TIS_DEFAULT_CANCELLATION, &priv->flags)) {
>> +		switch (priv->manufacturer_id) {
>> +		case TPM_VID_WINBOND:
>> +			return ((status == TPM_STS_VALID) ||
>> +				(status == (TPM_STS_VALID | TPM_STS_COMMAND_READY)));
>> +		case TPM_VID_STM:
>> +			return (status == (TPM_STS_VALID | TPM_STS_COMMAND_READY));
>> +		}
> Why there is no default: ?


Well I didn't want to duplicate the line "status == 
TPM_STS_COMMAND_READY" in the default case and for the flagged case. So 
now the switch just falls through for default. I can add default: break 
instead


>
>>   	}
>> +
>> +	return status == TPM_STS_COMMAND_READY;
>>   }
>>   
>>   static irqreturn_t tis_int_handler(int dummy, void *dev_id)
>> diff --git a/drivers/char/tpm/tpm_tis_core.h b/drivers/char/tpm/tpm_tis_core.h
>> index 66a5a13cd1df..b68479e0de10 100644
>> --- a/drivers/char/tpm/tpm_tis_core.h
>> +++ b/drivers/char/tpm/tpm_tis_core.h
>> @@ -86,6 +86,7 @@ enum tis_defaults {
>>   enum tpm_tis_flags {
>>   	TPM_TIS_ITPM_WORKAROUND		= BIT(0),
>>   	TPM_TIS_INVALID_STATUS		= BIT(1),
>> +	TPM_TIS_DEFAULT_CANCELLATION	= BIT(2),
>>   };
>>   
>>   struct tpm_tis_data {
>> diff --git a/drivers/char/tpm/tpm_tis_i2c.c b/drivers/char/tpm/tpm_tis_i2c.c
>> index 0692510dfcab..6722588e0217 100644
>> --- a/drivers/char/tpm/tpm_tis_i2c.c
>> +++ b/drivers/char/tpm/tpm_tis_i2c.c
>> @@ -329,6 +329,7 @@ static int tpm_tis_i2c_probe(struct i2c_client *dev,
>>   	if (!phy->io_buf)
>>   		return -ENOMEM;
>>   
>> +	set_bit(TPM_TIS_DEFAULT_CANCELLATION, &phy->priv.flags);
> What if you just zeroed manufacturer ID?


It's already zero there, and gets set to the VID as part of the core 
init function.


Thanks,

Eddie


>
>>   	phy->i2c_client = dev;
>>   
>>   	/* must precede all communication with the tpm */
>> -- 
>> 2.31.1
>>
> BR, Jarkko