Re: [PATCH] tpm: make locality handling resilient

["Daniel P. Smith" <dpsmith@apertussolutions.com>]

On 1/19/24 16:28, Jarkko Sakkinen wrote:
> On Mon Jan 15, 2024 at 1:15 AM UTC, Daniel P. Smith wrote:
>> Commit 933bfc5ad213 introduced the use of a locality counter to control when
>> locality request was actually sent to the TPM. This locality counter created a
>> hard enforcement that the TPM had no active locality at the time of the driver
>> initialization. The reality is that this may not always be the case coupled
>> with the fact that the commit indiscriminately decremented the counter created
>> the condition for integer underflow of the counter. The underflow was triggered
>> by the first pair of request/relinquish calls made in tpm_tis_init_core and all
>> subsequent calls to request/relinquished calls would have the counter flipping
>> between the underflow value and 0. The result is that it appeared all calls to
>> request/relinquish were successful, but they were not. The end result is that
>> the locality that was active when the driver loaded would always remain active,
>> to include after the driver shutdown. This creates a significant issue when
>> using Intel TXT and Locality 2 is active at boot. After the GETSEC[SEXIT]
>> instruction is called, the PCH will close access to Locality 2 MMIO address
>> space, leaving the TPM locked in Locality 2 with no means to relinquish the
>> locality until system reset.
>>
>> The commit seeks to address this situation through three changes. The first is
>> to walk the localities during initialization and close any open localities to
>> ensure the TPM is in the assumed state. Next is to put guards around the
>> counter and the requested locality to ensure they remain within valid values.
>> The last change is to make the request locality functions be consistent in
>> their return values. The functions will either return the locality requested if
>> successful or a negative error code.
>>
>> Signed-off-by: Daniel P. Smith <dpsmith@apertussolutions.com>
>> Signed-off-by: Ross Philipson <ross.philipson@oracle.com>
>> Reported-by: Kanth Ghatraju <kanth.ghatraju@oracle.com>
>> Fixes: 933bfc5ad213 ("tpm, tpm: Implement usage counter for locality")
>> ---
>>   drivers/char/tpm/tpm-chip.c     |  2 +-
>>   drivers/char/tpm/tpm_tis_core.c | 20 +++++++++++++++-----
>>   include/linux/tpm.h             |  2 ++
>>   3 files changed, 18 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
>> index 42b1062e33cd..e7293f85335a 100644
>> --- a/drivers/char/tpm/tpm-chip.c
>> +++ b/drivers/char/tpm/tpm-chip.c
>> @@ -49,7 +49,7 @@ static int tpm_request_locality(struct tpm_chip *chip)
>>   		return rc;
>>   
>>   	chip->locality = rc;
>> -	return 0;
>> +	return chip->locality;
>>   }
>>   
>>   static void tpm_relinquish_locality(struct tpm_chip *chip)
>> diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
>> index 1b350412d8a6..c8b9b0b199dc 100644
>> --- a/drivers/char/tpm/tpm_tis_core.c
>> +++ b/drivers/char/tpm/tpm_tis_core.c
>> @@ -180,7 +180,8 @@ static int tpm_tis_relinquish_locality(struct tpm_chip *chip, int l)
>>   	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
>>   
>>   	mutex_lock(&priv->locality_count_mutex);
>> -	priv->locality_count--;
>> +	if (priv->locality_count > 0)
>> +		priv->locality_count--;
>>   	if (priv->locality_count == 0)
>>   		__tpm_tis_relinquish_locality(priv, l);
>>   	mutex_unlock(&priv->locality_count_mutex);
>> @@ -226,18 +227,21 @@ static int __tpm_tis_request_locality(struct tpm_chip *chip, int l)
>>   			tpm_msleep(TPM_TIMEOUT);
>>   		} while (time_before(jiffies, stop));
>>   	}
>> -	return -1;
>> +	return -EBUSY;
>>   }
>>   
>>   static int tpm_tis_request_locality(struct tpm_chip *chip, int l)
>>   {
>>   	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
>> -	int ret = 0;
>> +	int ret = -EIO;
>> +
>> +	if (l > TPM_MAX_LOCALITY)
>> +		return -EINVAL;
>>   
>>   	mutex_lock(&priv->locality_count_mutex);
>>   	if (priv->locality_count == 0)
>>   		ret = __tpm_tis_request_locality(chip, l);
>> -	if (!ret)
>> +	if (ret >= 0)
>>   		priv->locality_count++;
>>   	mutex_unlock(&priv->locality_count_mutex);
>>   	return ret;
>> @@ -1108,7 +1112,7 @@ int tpm_tis_core_init(struct device *dev, struct tpm_tis_data *priv, int irq,
>>   	u32 intmask;
>>   	u32 clkrun_val;
>>   	u8 rid;
>> -	int rc, probe;
>> +	int rc, probe, locality;
> 
> s/locality/i/
> 
> We don't use long names for loop indices generally.

No problem, will change.

>>   	struct tpm_chip *chip;
>>   
>>   	chip = tpmm_chip_alloc(dev, &tpm_tis);
>> @@ -1169,6 +1173,12 @@ int tpm_tis_core_init(struct device *dev, struct tpm_tis_data *priv, int irq,
>>   		goto out_err;
>>   	}
>>   
>> +	/* It is not safe to assume localities are closed on startup */
> 
> This is somewhat useless comment.
> 
> E.g. this would be way more useful:
> 
> 	/*
> 	 * Intel TXT starts with locality 2 active. Therefore,
> 	 * localities cannot be assumed to be closed on startup.
> 	 */

Okay, will expand.

>> +	for (locality = 0; locality <= TPM_MAX_LOCALITY; locality++) {
>> +		if (check_locality(chip, locality))
>> +			tpm_tis_relinquish_locality(chip, locality);
>> +	}
>> +
>>   	/* Take control of the TPM's interrupt hardware and shut it off */
>>   	rc = tpm_tis_read32(priv, TPM_INT_ENABLE(priv->locality), &intmask);
>>   	if (rc < 0)
>> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
>> index 4ee9d13749ad..f2651281f02e 100644
>> --- a/include/linux/tpm.h
>> +++ b/include/linux/tpm.h
>> @@ -116,6 +116,8 @@ struct tpm_chip_seqops {
>>   	const struct seq_operations *seqops;
>>   };
>>   
>> +#define TPM_MAX_LOCALITY		4
> 
> Not documented.

Okay, will add spec ref.

>> +
>>   struct tpm_chip {
>>   	struct device dev;
>>   	struct device devs;
> 
> Thanks for the fix.

Your welcome.

> BR, Jarkko

V/r,
DPS