Re: [PATCH] tpm: fix ATMEL TPM crash caused by too frequent queries

From: Jarkko Sakkinen <jarkko@kernel.org>
To: Hao Wu <hao.wu@rubrik.com>
Cc: shrihari.kalkar@rubrik.com, seungyeop.han@rubrik.com,
	anish.jhaveri@rubrik.com, peterhuewe@gmx.de, jgg@ziepe.ca,
	linux-integrity@vger.kernel.org, pmenzel@molgen.mpg.de,
	kgold@linux.ibm.com, zohar@linux.vnet.ibm.com,
	why2jjj.linux@gmail.com, hamza@hpe.com,
	gregkh@linuxfoundation.org, arnd@arndb.de,
	nayna@linux.vnet.ibm.com, James.Bottomley@hansenpartnership.com
Subject: Re: [PATCH] tpm: fix ATMEL TPM crash caused by too frequent queries
Date: Fri, 2 Jul 2021 09:35:55 +0300	[thread overview]
Message-ID: <20210702063555.q2phirfv7wxc6axu@kernel.org> (raw)
In-Reply-To: <20210630042205.30051-1-hao.wu@rubrik.com>

On Tue, Jun 29, 2021 at 09:22:05PM -0700, Hao Wu wrote:
> This is a fix for the ATMEL TPM crash bug reported in
> https://patchwork.kernel.org/project/linux-integrity/patch/20200926223150.109645-1-hao.wu@rubrik.com/
> 
> According to the discussions in the original thread,
> we don't want to revert the timeout of wait_for_tpm_stat
> for non-ATMEL chips, which brings back the performance cost.
> For investigation and analysis of why wait_for_tpm_stat
> caused the issue, and how the regression was introduced,
> please read the original thread above.
> 
> Thus the proposed fix here is to only revert the timeout
> for ATMEL chips by checking the vendor ID.
> 
> Signed-off-by: Hao Wu <hao.wu@rubrik.com>
> Fixes: 9f3fc7bcddcb ("tpm: replace msleep() with usleep_range() in TPM 1.2/2.0 generic drivers")

Fixes tag should be before SOB.

> ---
> Test Plan:
> - Run fixed kernel with ATMEL TPM chips and see crash
> has been fixed.
> - Run fixed kernel with non-ATMEL TPM chips, and confirm
> the timeout has not been changed.
> 
>  drivers/char/tpm/tpm.h          |  9 ++++++++-
>  drivers/char/tpm/tpm_tis_core.c | 19 +++++++++++++++++--
>  include/linux/tpm.h             |  2 ++
>  3 files changed, 27 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
> index 283f78211c3a..bc6aa7f9e119 100644
> --- a/drivers/char/tpm/tpm.h
> +++ b/drivers/char/tpm/tpm.h
> @@ -42,7 +42,9 @@ enum tpm_timeout {
>  	TPM_TIMEOUT_RANGE_US = 300,	/* usecs */
>  	TPM_TIMEOUT_POLL = 1,	/* msecs */
>  	TPM_TIMEOUT_USECS_MIN = 100,      /* usecs */
> -	TPM_TIMEOUT_USECS_MAX = 500      /* usecs */
> +	TPM_TIMEOUT_USECS_MAX = 500,	/* usecs */

What is this change?

> +	TPM_TIMEOUT_WAIT_STAT = 500,	/* usecs */
> +	TPM_ATML_TIMEOUT_WAIT_STAT = 15000	/* usecs */
>  };
>  
>  /* TPM addresses */
> @@ -189,6 +191,11 @@ static inline void tpm_msleep(unsigned int delay_msec)
>  		     delay_msec * 1000);
>  };
>  
> +static inline void tpm_usleep(unsigned int delay_usec)
> +{
> +	usleep_range(delay_usec - TPM_TIMEOUT_RANGE_US, delay_usec);
> +};

Please remove this, and open code.

> +
>  int tpm_chip_start(struct tpm_chip *chip);
>  void tpm_chip_stop(struct tpm_chip *chip);
>  struct tpm_chip *tpm_find_get_ops(struct tpm_chip *chip);
> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
> index 55b9d3965ae1..9ddd4edfe1c2 100644
> --- a/drivers/char/tpm/tpm_tis_core.c
> +++ b/drivers/char/tpm/tpm_tis_core.c
> @@ -80,8 +80,12 @@ static int wait_for_tpm_stat(struct tpm_chip *chip, u8 mask,
>  		}
>  	} else {
>  		do {
> -			usleep_range(TPM_TIMEOUT_USECS_MIN,
> -				     TPM_TIMEOUT_USECS_MAX);
> +			if (chip->timeout_wait_stat && 
> +				chip->timeout_wait_stat >= TPM_TIMEOUT_WAIT_STAT) {
> +				tpm_usleep((unsigned int)(chip->timeout_wait_stat));
> +			} else {
> +				tpm_usleep((unsigned int)(TPM_TIMEOUT_WAIT_STAT));
> +			}

Invalid use of braces. Please read

https://www.kernel.org/doc/html/v5.13/process/coding-style.html

Why do you have to use this field conditionally anyway? Why doesn't
it always contain a legit value?

>  			status = chip->ops->status(chip);
>  			if ((status & mask) == mask)
>  				return 0;
> @@ -934,6 +938,8 @@ int tpm_tis_core_init(struct device *dev, struct tpm_tis_data *priv, int irq,
>  	chip->timeout_b = msecs_to_jiffies(TIS_TIMEOUT_B_MAX);
>  	chip->timeout_c = msecs_to_jiffies(TIS_TIMEOUT_C_MAX);
>  	chip->timeout_d = msecs_to_jiffies(TIS_TIMEOUT_D_MAX);
> +	/* init timeout for wait_for_tpm_stat */
> +	chip->timeout_wait_stat = TPM_TIMEOUT_WAIT_STAT;
>  	priv->phy_ops = phy_ops;
>  	dev_set_drvdata(&chip->dev, priv);
>  
> @@ -983,6 +989,15 @@ int tpm_tis_core_init(struct device *dev, struct tpm_tis_data *priv, int irq,
>  
>  	priv->manufacturer_id = vendor;
>  
> +	switch (priv->manufacturer_id) {
> +	case TPM_VID_ATML:
> +        /* ATMEL chip needs longer timeout to avoid crash */
> +		chip->timeout_wait_stat = TPM_ATML_TIMEOUT_WAIT_STAT;
> +		break;
> +	default:
> +		chip->timeout_wait_stat = TPM_TIMEOUT_WAIT_STAT;
> +	}
> +
>  	rc = tpm_tis_read8(priv, TPM_RID(0), &rid);
>  	if (rc < 0)
>  		goto out_err;
> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> index aa11fe323c56..35f2a0260d76 100644
> --- a/include/linux/tpm.h
> +++ b/include/linux/tpm.h
> @@ -150,6 +150,7 @@ struct tpm_chip {
>  	bool timeout_adjusted;
>  	unsigned long duration[TPM_NUM_DURATIONS]; /* jiffies */
>  	bool duration_adjusted;
> +	unsigned long timeout_wait_stat; /* usecs */
>  
>  	struct dentry *bios_dir[TPM_NUM_EVENT_LOG_FILES];
>  
> @@ -269,6 +270,7 @@ enum tpm2_cc_attrs {
>  #define TPM_VID_INTEL    0x8086
>  #define TPM_VID_WINBOND  0x1050
>  #define TPM_VID_STM      0x104A
> +#define TPM_VID_ATML     0x1114
>  
>  enum tpm_chip_flags {
>  	TPM_CHIP_FLAG_TPM2		= BIT(1),
> -- 
> 2.29.0.vfs.0.0
> 
> 

/Jarkko