Re: [PATCH v3 3/6] tpm: introduce tpm_pcr_bank_info structure with digest_size from TPM

[Roberto Sassu <roberto.sassu-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>]

On 6/23/2017 12:26 PM, Jarkko Sakkinen wrote:
> On Wed, Jun 21, 2017 at 04:29:38PM +0200, Roberto Sassu wrote:
>> This patch introduces the new structure tpm_pcr_bank_info to store
>> information regarding PCR banks. The next patch will replace the array of
>> TPM algorithms IDs with an array of the new structure.
>
> You should be able to express what you are doing without referring to
> the "next patch" as there is no well defined order between commits
> before they are in the mainline.
>
> In this you might considering merging couple of commits if they are
> so closely coupled.
>
>> tpm_pcr_bank_info contains the TPM algorithm ID, the digest size and,
>> optionally, the corresponding crypto ID, if a mapping exists. These
>
> There is probably not the one and only algorithm ID and digest. If I
> interperet this sentence to the word I would except either zero or one
> mappings in total.
>
>> information will be used by IMA to calculate the digest of an event
>> and to provide measurements logs to userspace applications. The new
>> structure has been defined in include/linux/tpm.h, as it will be passed
>> to functions outside the TPM driver.
>>
>> The purpose of this patch is to fix a serious issue in tpm2_pcr_extend():
>> if the mapping between a TPM algorithm and a crypto algorithm is not
>> defined, the PCR bank with the unknown algorithm is not extended.
>
> Don't really understand what you are trying to say here as this patch
> contains zero changes to tpm2_pcr_extend(). You shoud be carefuly when
> using strong words such as "serious". tpm2_pcr_extend() works in well
> defined way.

Providing to a remote attestation verifier a TPM quote with values
that do not reflect the true status of a system, to me seems
a serious issue.

Roberto


>> This gives the opportunity to an attacker to reply to remote attestation
>> requests with a list of fake measurements. Instead, the digest size
>> is retrieved from the output buffer of a PCR read, without relying
>> on the crypto subsystem.
>
> This last paragraph is total nonsense.
>
> I went through the whole commit message and did not find anything that
> would explain why you make the code changes. Seriously, if you don't
> know what you are doing it doesn't help if you explain alot of random
> stuff
>
> Maybe one way to explain part of the changes would be simply that the
> mapping is needed because kernel subsystems communicate with the crypto
> subsystem IDs. Just a one suggestion.
>
>> Signed-off-by: Roberto Sassu <roberto.sassu-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
>
>
>> ---
>>  drivers/char/tpm/tpm.h      | 11 -----------
>>  drivers/char/tpm/tpm2-cmd.c | 30 ++++++++++++++++++++++++++++++
>>  include/linux/tpm.h         | 19 +++++++++++++++++++
>>  3 files changed, 49 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
>> index 1df0521..62c600d 100644
>> --- a/drivers/char/tpm/tpm.h
>> +++ b/drivers/char/tpm/tpm.h
>> @@ -98,17 +98,6 @@ enum tpm2_return_codes {
>>  	TPM2_RC_REFERENCE_H0	= 0x0910,
>>  };
>>
>> -enum tpm2_algorithms {
>> -	TPM2_ALG_ERROR		= 0x0000,
>> -	TPM2_ALG_SHA1		= 0x0004,
>> -	TPM2_ALG_KEYEDHASH	= 0x0008,
>> -	TPM2_ALG_SHA256		= 0x000B,
>> -	TPM2_ALG_SHA384		= 0x000C,
>> -	TPM2_ALG_SHA512		= 0x000D,
>> -	TPM2_ALG_NULL		= 0x0010,
>> -	TPM2_ALG_SM3_256	= 0x0012,
>> -};
>> -
>>  enum tpm2_command_codes {
>>  	TPM2_CC_FIRST		= 0x011F,
>>  	TPM2_CC_SELF_TEST	= 0x0143,
>> diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
>> index 6a9fe0d..74a68ea 100644
>> --- a/drivers/char/tpm/tpm2-cmd.c
>> +++ b/drivers/char/tpm/tpm2-cmd.c
>> @@ -992,6 +992,36 @@ int tpm2_probe(struct tpm_chip *chip)
>>  }
>>  EXPORT_SYMBOL_GPL(tpm2_probe);
>>
>> +static int tpm2_init_pcr_bank_info(struct tpm_chip *chip, u16 alg_id,
>> +				   struct tpm_pcr_bank_info *active_bank)
>
> Generates a compiler warning (unused function).
>
>> +{
>> +	struct tpm_buf buf;
>> +	struct tpm2_pcr_read_out *pcrread_out;
>> +	int rc = 0;
>> +	int i;
>> +
>> +	active_bank->alg_id = alg_id;
>> +
>> +	rc = tpm2_pcr_read_tpm_buf(chip, 0, alg_id, &buf, NULL);
>> +	if (rc)
>> +		goto out;
>> +
>> +	pcrread_out = (struct tpm2_pcr_read_out *)&buf.data[TPM_HEADER_SIZE];
>> +
>> +	active_bank->digest_size = be16_to_cpu(pcrread_out->digest_size);
>> +	active_bank->crypto_id = HASH_ALGO__LAST;
>> +
>> +	for (i = 0; i < ARRAY_SIZE(tpm2_hash_map); i++) {
>> +		if (active_bank->alg_id != tpm2_hash_map[i].tpm_id)
>> +			continue;
>> +
>> +		active_bank->crypto_id = tpm2_hash_map[i].crypto_id;
>> +	}
>> +out:
>> +	tpm_buf_destroy(&buf);
>> +	return rc;
>> +}
>> +
>>  struct tpm2_pcr_selection {
>>  	__be16  hash_alg;
>>  	u8  size_of_select;
>> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
>> index 5a090f5..ff06738 100644
>> --- a/include/linux/tpm.h
>> +++ b/include/linux/tpm.h
>> @@ -22,6 +22,8 @@
>>  #ifndef __LINUX_TPM_H__
>>  #define __LINUX_TPM_H__
>>
>> +#include <crypto/hash_info.h>
>> +
>>  #define TPM_DIGEST_SIZE 20	/* Max TPM v1.2 PCR size */
>>
>>  /*
>> @@ -37,6 +39,17 @@ enum TPM_OPS_FLAGS {
>>  	TPM_OPS_AUTO_STARTUP = BIT(0),
>>  };
>>
>> +enum tpm2_algorithms {
>> +	TPM2_ALG_ERROR		= 0x0000,
>> +	TPM2_ALG_SHA1		= 0x0004,
>> +	TPM2_ALG_KEYEDHASH	= 0x0008,
>> +	TPM2_ALG_SHA256		= 0x000B,
>> +	TPM2_ALG_SHA384		= 0x000C,
>> +	TPM2_ALG_SHA512		= 0x000D,
>> +	TPM2_ALG_NULL		= 0x0010,
>> +	TPM2_ALG_SM3_256	= 0x0012,
>> +};
>> +
>>  struct tpm_class_ops {
>>  	unsigned int flags;
>>  	const u8 req_complete_mask;
>> @@ -52,6 +65,12 @@ struct tpm_class_ops {
>>  	void (*relinquish_locality)(struct tpm_chip *chip, int loc);
>>  };
>>
>> +struct tpm_pcr_bank_info {
>> +	enum tpm2_algorithms alg_id;
>> +	enum hash_algo crypto_id;
>> +	u32 digest_size;
>> +};
>> +
>>  #if defined(CONFIG_TCG_TPM) || defined(CONFIG_TCG_TPM_MODULE)
>>
>>  extern int tpm_is_tpm2(u32 chip_num);
>> --
>> 2.9.3
>>
>
> The code changes does not "live for its own".
>
> /Jarkko
>

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