Re: [PATCH v2 3/3] tpm: retrieve digest size of unknown algorithms with PCR read

Re: [PATCH v2 3/3] tpm: retrieve digest size of unknown algorithms with PCR read

[Roberto Sassu]

On 9/16/2018 2:37 PM, Jarkko Sakkinen wrote:
> On Wed, Sep 05, 2018 at 01:42:02PM +0200, Roberto Sassu wrote:
>> Currently, the TPM driver retrieves the digest size from a table mapping
>> TPM algorithms identifiers to identifiers defined by the crypto subsystem.
>> If the algorithm is not defined by the latter, the digest size can be
>> retrieved from the output of the PCR read command.
>>
>> The patch retrieves at TPM startup the digest sizes for each PCR bank and
>> stores them in the new structure tpm_active_bank_info, member of tpm_chip,
>> so that the information can be passed to other kernel subsystems.
>>
>> tpm_active_bank_info contains: the TPM algorithm identifier, necessary to
>> generate the event log as defined by Trusted Computing Group (TCG); the
>> digest size, to pad/truncate a digest calculated with a different
>> algorithm; the crypto subsystem identifier, to calculate the digest of
>> event data.
>>
>> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
>> ---
>>   drivers/char/tpm/tpm-interface.c | 11 +++++++---
>>   drivers/char/tpm/tpm.h           |  4 ++--
>>   drivers/char/tpm/tpm2-cmd.c      | 47 ++++++++++++++++++++++++++++++----------
>>   include/linux/tpm.h              |  6 +++++
>>   4 files changed, 51 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
>> index 81872880b5f1..02dcdcda5a3c 100644
>> --- a/drivers/char/tpm/tpm-interface.c
>> +++ b/drivers/char/tpm/tpm-interface.c
>> @@ -993,7 +993,7 @@ int tpm_pcr_read(struct tpm_chip *chip, int pcr_idx, u32 count,
>>   	if (!chip)
>>   		return -ENODEV;
>>   	if (chip->flags & TPM_CHIP_FLAG_TPM2)
>> -		rc = tpm2_pcr_read(chip, pcr_idx, count, digests);
>> +		rc = tpm2_pcr_read(chip, pcr_idx, count, digests, NULL);
>>   	else
>>   		rc = tpm_pcr_read_dev(chip, pcr_idx, digests[0].digest);
>>   	tpm_put_ops(chip);
>> @@ -1056,8 +1056,8 @@ int tpm_pcr_extend(struct tpm_chip *chip, int pcr_idx, const u8 *hash)
>>   		memset(digest_list, 0, sizeof(digest_list));
>>   
>>   		for (i = 0; i < ARRAY_SIZE(chip->active_banks) &&
>> -			    chip->active_banks[i] != TPM_ALG_ERROR; i++) {
>> -			digest_list[i].alg_id = chip->active_banks[i];
>> +		     chip->active_banks[i].alg_id != TPM_ALG_ERROR; i++) {
>> +			digest_list[i].alg_id = chip->active_banks[i].alg_id;
> 
> Why not just zero?

Hi Jarkko

sorry, I didn't understand this comment. Did you refer to the code
below (chip->active_banks[0] ...)?


>>   			memcpy(digest_list[i].digest, hash, TPM_DIGEST_SIZE);
>>   			count++;
>>   		}
>> @@ -1158,6 +1158,11 @@ int tpm1_auto_startup(struct tpm_chip *chip)
>>   		goto out;
>>   	}
>>   
>> +	chip->active_banks[0].alg_id = TPM_ALG_SHA1;
>> +	chip->active_banks[0].digest_size = hash_digest_size[HASH_ALGO_SHA1];
>> +	chip->active_banks[0].crypto_id = HASH_ALGO_SHA1;
>> +	chip->active_banks[1].alg_id = TPM_ALG_ERROR;
> 
> Then you could drop the last line here.

This code has the same behavior of tpm2_get_pcr_allocation(). If some
banks are not used, set the algorithm of the first unused to
TPM_ALG_ERROR.


>> +
>>   	return rc;
>>   out:
>>   	if (rc > 0)
>> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
>> index 9479e1ae1b4c..385843b49c17 100644
>> --- a/drivers/char/tpm/tpm.h
>> +++ b/drivers/char/tpm/tpm.h
>> @@ -237,7 +237,7 @@ struct tpm_chip {
>>   	const struct attribute_group *groups[3];
>>   	unsigned int groups_cnt;
>>   
>> -	u16 active_banks[7];
>> +	struct tpm_active_bank_info active_banks[7];
>>   #ifdef CONFIG_ACPI
>>   	acpi_handle acpi_dev_handle;
>>   	char ppi_version[TPM_PPI_VERSION_LEN + 1];
>> @@ -565,7 +565,7 @@ static inline u32 tpm2_rc_value(u32 rc)
>>   }
>>   
>>   int tpm2_pcr_read(struct tpm_chip *chip, int pcr_idx, u32 count,
>> -		  struct tpm_digest *digests);
>> +		  struct tpm_digest *digests, u16 *sizes);
>>   int tpm2_pcr_extend(struct tpm_chip *chip, int pcr_idx, u32 count,
>>   		    struct tpm_digest *digests);
>>   int tpm2_get_random(struct tpm_chip *chip, u8 *dest, size_t max);
>> diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
>> index 601d67c76c1e..51d2454c5329 100644
>> --- a/drivers/char/tpm/tpm2-cmd.c
>> +++ b/drivers/char/tpm/tpm2-cmd.c
>> @@ -181,11 +181,12 @@ struct tpm2_pcr_read_out {
>>    * @pcr_idx:	index of the PCR to read.
>>    * @count:	number of digests passed.
>>    * @digests:	list of pcr banks and buffers current PCR values are written to.
>> + * @sizes:	list of digest sizes.
>>    *
>>    * Return: Same as with tpm_transmit_cmd.
>>    */
>>   int tpm2_pcr_read(struct tpm_chip *chip, int pcr_idx, u32 count,
>> -		  struct tpm_digest *digests)
>> +		  struct tpm_digest *digests, u16 *sizes)
>>   {
>>   	int rc;
>>   	struct tpm_buf buf;
>> @@ -215,6 +216,9 @@ int tpm2_pcr_read(struct tpm_chip *chip, int pcr_idx, u32 count,
>>   		out = (struct tpm2_pcr_read_out *)&buf.data[TPM_HEADER_SIZE];
>>   		memcpy(digests[0].digest, out->digest,
>>   		       be16_to_cpu(out->digest_size));
>> +
>> +		if (sizes)
>> +			sizes[0] = be16_to_cpu(out->digest_size);
>>   	}
>>   
>>   	tpm_buf_destroy(&buf);
>> @@ -245,7 +249,6 @@ int tpm2_pcr_extend(struct tpm_chip *chip, int pcr_idx, u32 count,
>>   	struct tpm2_null_auth_area auth_area;
>>   	int rc;
>>   	int i;
>> -	int j;
>>   
>>   	if (count > ARRAY_SIZE(chip->active_banks))
>>   		return -EINVAL;
>> @@ -267,14 +270,9 @@ int tpm2_pcr_extend(struct tpm_chip *chip, int pcr_idx, u32 count,
>>   	tpm_buf_append_u32(&buf, count);
>>   
>>   	for (i = 0; i < count; i++) {
>> -		for (j = 0; j < ARRAY_SIZE(tpm2_hash_map); j++) {
>> -			if (digests[i].alg_id != tpm2_hash_map[j].tpm_id)
>> -				continue;
>> -			tpm_buf_append_u16(&buf, digests[i].alg_id);
>> -			tpm_buf_append(&buf, (const unsigned char
>> -					      *)&digests[i].digest,
>> -			       hash_digest_size[tpm2_hash_map[j].crypto_id]);
>> -		}
>> +		tpm_buf_append_u16(&buf, digests[i].alg_id);
>> +		tpm_buf_append(&buf, (const unsigned char *)&digests[i].digest,
>> +			       chip->active_banks[i].digest_size);
>>   	}
>>   
>>   	rc = tpm_transmit_cmd(chip, NULL, buf.data, PAGE_SIZE, 0, 0,
>> @@ -851,6 +849,26 @@ int tpm2_probe(struct tpm_chip *chip)
>>   }
>>   EXPORT_SYMBOL_GPL(tpm2_probe);
>>   
>> +static int tpm2_init_active_bank_info(struct tpm_chip *chip,
>> +				      struct tpm_active_bank_info *active_bank)
>> +{
>> +	struct tpm_digest digest = {.alg_id = active_bank->alg_id};
>> +	int i;
>> +
>> +	for (i = 0; i < ARRAY_SIZE(tpm2_hash_map); i++) {
>> +		enum hash_algo crypto_algo = tpm2_hash_map[i].crypto_id;
>> +
>> +		if (active_bank->alg_id != tpm2_hash_map[i].tpm_id)
>> +			continue;
>> +
>> +		active_bank->digest_size = hash_digest_size[crypto_algo];
>> +		active_bank->crypto_id = crypto_algo;
>> +		return 0;
>> +	}
>> +
>> +	return tpm2_pcr_read(chip, 0, 1, &digest, &active_bank->digest_size);
>> +}
>> +
>>   struct tpm2_pcr_selection {
>>   	__be16  hash_alg;
>>   	u8  size_of_select;
>> @@ -905,7 +923,12 @@ static ssize_t tpm2_get_pcr_allocation(struct tpm_chip *chip)
>>   		}
>>   
>>   		memcpy(&pcr_selection, marker, sizeof(pcr_selection));
>> -		chip->active_banks[i] = be16_to_cpu(pcr_selection.hash_alg);
>> +		chip->active_banks[i].alg_id =
>> +			be16_to_cpu(pcr_selection.hash_alg);
>> +		rc =  tpm2_init_active_bank_info(chip, &chip->active_banks[i]);
>> +		if (rc)
>> +			break;
>> +
>>   		sizeof_pcr_selection = sizeof(pcr_selection.hash_alg) +
>>   			sizeof(pcr_selection.size_of_select) +
>>   			pcr_selection.size_of_select;
>> @@ -914,7 +937,7 @@ static ssize_t tpm2_get_pcr_allocation(struct tpm_chip *chip)
>>   
>>   out:
>>   	if (i < ARRAY_SIZE(chip->active_banks))
>> -		chip->active_banks[i] = TPM_ALG_ERROR;
>> +		chip->active_banks[i].alg_id = TPM_ALG_ERROR;
>>   
>>   	tpm_buf_destroy(&buf);
>>   
>> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
>> index ac9fc47f4494..c8372ff582c3 100644
>> --- a/include/linux/tpm.h
>> +++ b/include/linux/tpm.h
>> @@ -46,6 +46,12 @@ struct tpm_digest {
>>   	u8 digest[SHA512_DIGEST_SIZE];
>>   } __packed;
>>   
>> +struct tpm_active_bank_info {
>> +	u16 alg_id;
>> +	u16 digest_size;
>> +	u16 crypto_id;
>> +};
> 
> Why not just tpm_bank_info? Will there be also tpm_inactive_bank_info
> at some point?

It derived from chip->active_banks. I will rename the structure.

Thanks

Roberto

Re: [PATCH v2 3/3] tpm: retrieve digest size of unknown algorithms with PCR read

[Jarkko Sakkinen]

On Mon, Sep 17, 2018 at 12:02:56PM +0200, Roberto Sassu wrote:
> This code has the same behavior of tpm2_get_pcr_allocation(). If some
> banks are not used, set the algorithm of the first unused to
> TPM_ALG_ERROR.

My point is that maybe it would sense to use zero for that in order
to make code a bit simpler.

/Jarkko

Re: [PATCH v2 3/3] tpm: retrieve digest size of unknown algorithms with PCR read

[Roberto Sassu]

On 9/17/2018 11:16 PM, Jarkko Sakkinen wrote:
> On Mon, Sep 17, 2018 at 12:02:56PM +0200, Roberto Sassu wrote:
>> This code has the same behavior of tpm2_get_pcr_allocation(). If some
>> banks are not used, set the algorithm of the first unused to
>> TPM_ALG_ERROR.
> 
> My point is that maybe it would sense to use zero for that in order
> to make code a bit simpler.

Wouldn't be better to compare data with the same type? Since the alg_id
structure member stores an algorithm, it should be fine to compare its
value with an algorithm.

No problem to change that, but probably I should modify also
tpm_pcr_extend().

Roberto

Re: [PATCH v2 3/3] tpm: retrieve digest size of unknown algorithms with PCR read

[Jarkko Sakkinen]

On Tue, Sep 18, 2018 at 09:14:43AM +0200, Roberto Sassu wrote:
> On 9/17/2018 11:16 PM, Jarkko Sakkinen wrote:
> > On Mon, Sep 17, 2018 at 12:02:56PM +0200, Roberto Sassu wrote:
> > > This code has the same behavior of tpm2_get_pcr_allocation(). If some
> > > banks are not used, set the algorithm of the first unused to
> > > TPM_ALG_ERROR.
> > 
> > My point is that maybe it would sense to use zero for that in order
> > to make code a bit simpler.
> 
> Wouldn't be better to compare data with the same type? Since the alg_id
> structure member stores an algorithm, it should be fine to compare its
> value with an algorithm.
> 
> No problem to change that, but probably I should modify also
> tpm_pcr_extend().
> 
> Roberto

Please do.

/Jarkko

Re: EXTERNAL: [PATCH v2 2/3] tpm: modify tpm_pcr_read() definition to pass TPM hash algorithms

[Roberto Sassu]

On 9/26/2018 4:09 PM, Mimi Zohar wrote:
> On Wed, 2018-09-05 at 17:03 +0200, Roberto Sassu wrote:
>> On 9/5/2018 3:43 PM, Jeremy Boone wrote:
>>> Some comments on tpm2_pcr_read below.
>>>
>>> The tpm2_pcr_read function uses TPM2_ST_NO_SESSIONS. This means
>> that the response payload is not integrity protected with an HMAC.
>> If there is a man-in-the-middle sitting on the serial bus that
>> connects the TPM peripheral to the processor, they can tamper with
>> the response parameters.
>>>   
>>> In your changes to tpm2_pcr_read, the memcpy is now become a
>> variable-length operation, instead of just copying a fixed number of
>> bytes. If the MITM modifies the response field out->digest_size
>> before it is received by the driver, they can make it a very large
>> value, forcing a buffer overflow of the out->digest array.
>>>   
>>> Adding a session to the PCR Read command seems like overkill in
>> this case. I wouldn’t recommend that as a solution here.  So to fix
>> this I would suggest simply checking the digest size before the
>> memcpy.
>>
>> Hi Jeremy
>>
>> ok, thanks.
> 
> The hash digest size checking should be based on the size stored in
> the active_bank_info, either in 3/3 or as a separate patch.

This can be done after the PCR read requested by
tpm2_init_active_bank_info() to initialize the digest sizes.

Roberto