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

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Message-ID: <Yxl8CJBZiROgqhd6@kernel.org>
Date:   Thu, 8 Sep 2022 08:22:16 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Eddie James <eajames@...ux.ibm.com>
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 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: ?

>  	}
> +
> +	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?

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

BR, Jarkko