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

[Hao Wu <hao.wu@rubrik.com>]

> On Jul 1, 2021, at 11:35 PM, Jarkko Sakkinen <jarkko@kernel.org> wrote:
> 
> 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?
Need to add the tailing comma

> 
>> +	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.
Ok, will do

>> +
>> 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?
The field is legit now, but doesn’t hurt to do addition check for robustness 
to ensure no crash ? Just in case the value is updated below TPM_TIMEOUT_WAIT_STAT ? 

Can remove if we think it is not needed.

> 
>> 			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 */
Will fix the indentation

Also according to Kenneth we only want to do so for TPM 1.2, 
I will try checking chip->flags against TPM_CHIP_FLAG_TPM2 here
Let me know if there are concerns.
 
>> +		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