linux-kernel - Re: [PATCH] tpm_tis_core: Choose appropriate timeout for reading burstcount

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Message-ID: <20170222211301.wnm5mb52civnmcdj@intel.com>
Date:   Wed, 22 Feb 2017 23:13:01 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Peter Huewe <peter.huewe@...ineon.com>
Cc:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        tpmdd-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        peterhuewe@....de,
        Alexander Steffen <Alexander.Steffen@...ineon.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] tpm_tis_core: Choose appropriate timeout for reading
 burstcount

On Thu, Feb 16, 2017 at 03:33:36PM +0000, Peter Huewe wrote:
> From: Alexander Steffen <Alexander.Steffen@...ineon.com>
> 
> TIS v1.3 for TPM 1.2 and PTP for TPM 2.0 disagree about which timeout
> value applies to reading a valid burstcount. It is TIMEOUT_D according to
> TIS, but TIMEOUT_A according to PTP, so choose the appropriate value
> depending on whether we deal with a TPM 1.2 or a TPM 2.0.
> 
> This is important since according to the PTP TIMEOUT_D is much smaller
> than TIMEOUT_A. So the previous implementation could run into timeouts
> with a TPM 2.0, even though the TPM was behaving perfectly fine.
> 
> During tpm2_probe TIMEOUT_D will be used even with a TPM 2.0, because
> TPM_CHIP_FLAG_TPM2 is not yet set. This is fine, since the timeout values
> will only be changed afterwards by tpm_get_timeouts. Until then
> TIS_TIMEOUT_D_MAX applies, which is large enough.
> 
> Cc: stable@...r.kernel.org
> Fixes: aec04cbdf723 ("tpm: TPM 2.0 FIFO Interface")
> 
> Signed-off-by: Alexander Steffen <Alexander.Steffen@...ineon.com>
> Signed-off-by: Peter Huewe <peter.huewe@...ineon.com>

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

/Jarkko

> ---
>  drivers/char/tpm/tpm_tis_core.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index c0f296b5d413..fc0e9a2734ed 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -160,8 +160,10 @@ static int get_burstcount(struct tpm_chip *chip)
>  	u32 value;
>  
>  	/* wait for burstcount */
> -	/* which timeout value, spec has 2 answers (c & d) */
> -	stop = jiffies + chip->timeout_d;
> +	if (chip->flags & TPM_CHIP_FLAG_TPM2)
> +		stop = jiffies + chip->timeout_a;
> +	else
> +		stop = jiffies + chip->timeout_d;
>  	do {
>  		rc = tpm_tis_read32(priv, TPM_STS(priv->locality), &value);
>  		if (rc < 0)
> -- 
> 2.7.4
>