[tpmdd-devel,v3,1/2] tpm_tis_core: add optional max xfer size check

If tpm reports a bigger burstcnt than allowed by the physical protocol,
set burstcnt to the max allowed value.

In practice, seen in case of xfer issues (e.g. in spi interface case,
lost header causing flow control issues and wrong values returned on read
from TPM_STS). Without catching, causes the physical layer to reject xfer.

Signed-off-by: Andrey Pronin <apronin@chromium.org>
---
 drivers/char/tpm/tpm_tis_core.c | 9 ++++++++-
 drivers/char/tpm/tpm_tis_core.h | 1 +
 2 files changed, 9 insertions(+), 1 deletion(-)

On Wed, Jul 27, 2016 at 08:49:56PM -0700, Andrey Pronin wrote:
> If tpm reports a bigger burstcnt than allowed by the physical protocol,
> set burstcnt to the max allowed value.
> 
> In practice, seen in case of xfer issues (e.g. in spi interface case,
> lost header causing flow control issues and wrong values returned on read
> from TPM_STS). Without catching, causes the physical layer to reject xfer.
> 
> Signed-off-by: Andrey Pronin <apronin@chromium.org>
> ---
>  drivers/char/tpm/tpm_tis_core.c | 9 ++++++++-
>  drivers/char/tpm/tpm_tis_core.h | 1 +
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index f22caf8..7c4fa0c 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -168,8 +168,15 @@ static int get_burstcount(struct tpm_chip *chip)
>  			return rc;
>  
>  		burstcnt = (value >> 8) & 0xFFFF;
> -		if (burstcnt)
> +		if (burstcnt) {
> +			if (priv->phy_ops->max_xfer_size &&
> +			    (burstcnt > priv->phy_ops->max_xfer_size)) {

This does not actually need parentheses, otehrwise:

Reviewed-by: Dmitry Torokhov <dtor@chromium.org>

> +				dev_warn(&chip->dev,
> +					 "Bad burstcnt read: %d\n", burstcnt);
> +				burstcnt = priv->phy_ops->max_xfer_size;
> +			}
>  			return burstcnt;
> +		}
>  		msleep(TPM_TIMEOUT);
>  	} while (time_before(jiffies, stop));
>  	return -EBUSY;
> diff --git a/drivers/char/tpm/tpm_tis_core.h b/drivers/char/tpm/tpm_tis_core.h
> index 9191aab..58e8b14 100644
> --- a/drivers/char/tpm/tpm_tis_core.h
> +++ b/drivers/char/tpm/tpm_tis_core.h
> @@ -102,6 +102,7 @@ struct tpm_tis_phy_ops {
>  	int (*read16)(struct tpm_tis_data *data, u32 addr, u16 *result);
>  	int (*read32)(struct tpm_tis_data *data, u32 addr, u32 *result);
>  	int (*write32)(struct tpm_tis_data *data, u32 addr, u32 src);
> +	u16 max_xfer_size;
>  };
>  
>  static inline int tpm_tis_read_bytes(struct tpm_tis_data *data, u32 addr,
> -- 
> 2.6.6
>

On Wed, Jul 27, 2016 at 08:49:56PM -0700, Andrey Pronin wrote:
> If tpm reports a bigger burstcnt than allowed by the physical protocol,
> set burstcnt to the max allowed value.
> 
> In practice, seen in case of xfer issues (e.g. in spi interface case,
> lost header causing flow control issues and wrong values returned on read
> from TPM_STS). Without catching, causes the physical layer to reject xfer.
> 
> Signed-off-by: Andrey Pronin <apronin@chromium.org>

Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

I don't have hardware to test this. Someone should validate that it
does not break anything. Christophe, are you able to do this?

/Jarkko

> ---
>  drivers/char/tpm/tpm_tis_core.c | 9 ++++++++-
>  drivers/char/tpm/tpm_tis_core.h | 1 +
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index f22caf8..7c4fa0c 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -168,8 +168,15 @@ static int get_burstcount(struct tpm_chip *chip)
>  			return rc;
>  
>  		burstcnt = (value >> 8) & 0xFFFF;
> -		if (burstcnt)
> +		if (burstcnt) {
> +			if (priv->phy_ops->max_xfer_size &&
> +			    (burstcnt > priv->phy_ops->max_xfer_size)) {
> +				dev_warn(&chip->dev,
> +					 "Bad burstcnt read: %d\n", burstcnt);
> +				burstcnt = priv->phy_ops->max_xfer_size;
> +			}
>  			return burstcnt;
> +		}
>  		msleep(TPM_TIMEOUT);
>  	} while (time_before(jiffies, stop));
>  	return -EBUSY;
> diff --git a/drivers/char/tpm/tpm_tis_core.h b/drivers/char/tpm/tpm_tis_core.h
> index 9191aab..58e8b14 100644
> --- a/drivers/char/tpm/tpm_tis_core.h
> +++ b/drivers/char/tpm/tpm_tis_core.h
> @@ -102,6 +102,7 @@ struct tpm_tis_phy_ops {
>  	int (*read16)(struct tpm_tis_data *data, u32 addr, u16 *result);
>  	int (*read32)(struct tpm_tis_data *data, u32 addr, u32 *result);
>  	int (*write32)(struct tpm_tis_data *data, u32 addr, u32 src);
> +	u16 max_xfer_size;
>  };
>  
>  static inline int tpm_tis_read_bytes(struct tpm_tis_data *data, u32 addr,
> -- 
> 2.6.6
> 

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