Re: [PATCH v2] tpm: check selftest status before retrying full selftest

[Jarkko Sakkinen]

On Mon, May 07, 2018 at 09:09:41PM +0530, Nayna Jain wrote:
> As per the TCG Specification[1][2], RC_COMMAND_CODE indicates that the TPM
> command is not implemented or not supported. When RC_COMMAND_CODE is
> returned in response to the partial selftest, this is not the case. TPM 2.0
> supports TPM2_GetTestResult[3], which can be used to check the selftest
> status before sending the full selftest command.
> 
> This patch implements the tpm2_get_selftest_result function to check the
> selftest status when partial selftest returns RC_COMMAND_CODE.

Cosmetic: parentheses when referring to functions.

> This change results in finishing of the selftest much earlier compared to
> the existing case where full selftest is immediately sent to retry. The
> Pi's dmesg shows: the TPM selftest completed at 1.243864 secs compared
> with the previous timestamp of 1.939667 secs.
> 
> [1] As per the TCG Specification, Trusted Platform Module Library,
> Part 2 - Structures, Section 6.6.3 and Section 4.18:
> 
> "RC_COMMAND_CODE indicates the response code that is returned if the TPM is
> unmarshalling a value that it expects to be a TPM_CC and the input value is
> not in the table."
> 
> [2] As per the TCG Specification, Trusted Platform Module Library,
> Part 2 - Commands, Section 5.2:
> 
> "The TPM shall successfully unmarshal a TPM_CC and verify that the command
> is implemented (TPM_RC_COMMAND_CODE)."
> 
> [3] As per the TCG Specification, Trusted Platform Module Library,
> Part 2 - Commands, Section 10.4:
> 
> "This command(TPM2_GetTestResult) returns manufacturer-specific information
> regarding the results of a self-test and an indication of the test status."
> 
> Signed-off-by: Nayna Jain <nayna@xxxxxxxxxxxxxxxxxx>
> Tested-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> (on Pi with TPM 2.0)
> ---
> 
> Changelog v2:
> * changed the subject and updated patch description
> * removed the logs
> 
>  drivers/char/tpm/tpm.h      |  2 ++
>  drivers/char/tpm/tpm2-cmd.c | 48 +++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 50 insertions(+)
> 
> diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
> index af3bb87d3ea1..1de4240b52c4 100644
> --- a/drivers/char/tpm/tpm.h
> +++ b/drivers/char/tpm/tpm.h
> @@ -114,6 +114,7 @@ enum tpm2_return_codes {
>  	TPM2_RC_FAILURE		= 0x0101,
>  	TPM2_RC_DISABLED	= 0x0120,
>  	TPM2_RC_COMMAND_CODE    = 0x0143,
> +	TPM2_RC_NEEDS_TEST      = 0x0153,
>  	TPM2_RC_TESTING		= 0x090A, /* RC_WARN */
>  	TPM2_RC_REFERENCE_H0	= 0x0910,
>  	TPM2_RC_RETRY		= 0x0922,
> @@ -144,6 +145,7 @@ enum tpm2_command_codes {
>  	TPM2_CC_FLUSH_CONTEXT	= 0x0165,
>  	TPM2_CC_GET_CAPABILITY	= 0x017A,
>  	TPM2_CC_GET_RANDOM	= 0x017B,
> +	TPM2_CC_GET_TEST_RESULT = 0x017C,
>  	TPM2_CC_PCR_READ	= 0x017E,
>  	TPM2_CC_PCR_EXTEND	= 0x0182,
>  	TPM2_CC_LAST		= 0x018F,
> diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> index 96c77c8e7f40..4abba0ebe25b 100644
> --- a/drivers/char/tpm/tpm2-cmd.c
> +++ b/drivers/char/tpm/tpm2-cmd.c
> @@ -825,6 +825,50 @@ unsigned long tpm2_calc_ordinal_duration(struct tpm_chip *chip, u32 ordinal)
>  EXPORT_SYMBOL_GPL(tpm2_calc_ordinal_duration);
>  
>  /**
> + * tpm2_get_selftest_result() - get the status of self tests
> + *

There should not be an empty line here.

> + * @chip: TPM chip to use
> + *
> + * Return: If error return rc, else return the result of the self tests.
> + * TPM_RC_NEEDS_TESTING: No self tests are done. Needs testing.
> + * TPM_RC_TESTING: Self tests are in progress.
> + * TPM_RC_SUCCESS: Self tests completed successfully.
> + * TPM_RC_FAILURE: Self tests completed failure.
> + *
> + * This function can be used to check the status of self tests on the TPM.
> + */

Description should 

Better to just have:

Return:
  TPM return code,
  -errno otherwise
 
There is a lot of variance in return values but this is the format where
I would like the code base to dilate to. Describing TPM return codes
one by one is not very maintainable in the long run.

See:
https://www.kernel.org/doc/Documentation/kernel-doc-nano-HOWTO.txt


> +static int tpm2_get_selftest_result(struct tpm_chip *chip)
> +{
> +	struct tpm_buf buf;
> +	int rc;
> +	int test_result;
> +	uint16_t data_size;
> +	int len;
> +	const struct tpm_output_header *header;
> +
> +	rc = tpm_buf_init(&buf, TPM2_ST_NO_SESSIONS, TPM2_CC_GET_TEST_RESULT);
> +	if (rc)
> +		return rc;
> +
> +	len = tpm_transmit(chip, NULL, buf.data, PAGE_SIZE, 0);
> +	if (len <  0)
> +		return len;
> +
> +	header = (struct tpm_output_header *)buf.data;
> +
> +	rc = be32_to_cpu(header->return_code);
> +	if (rc)
> +		return rc;
> +
> +	data_size = be16_to_cpup((__be16 *)&buf.data[TPM_HEADER_SIZE]);
> +
> +	test_result = be32_to_cpup((__be32 *)
> +			(&buf.data[TPM_HEADER_SIZE + 2 + data_size]));
> +
> +	return test_result;
> +}
> +
> +/**
>   * tpm2_do_selftest() - ensure that all self tests have passed
>   *
>   * @chip: TPM chip to use
> @@ -853,6 +897,10 @@ static int tpm2_do_selftest(struct tpm_chip *chip)
>  				      "attempting the self test");
>  		tpm_buf_destroy(&buf);
>  
> +		/* Check the selftest status */

What is the purpose of this comment eg what does it describe that isn't
obvious?

> +		if (rc == TPM2_RC_COMMAND_CODE)
> +			rc = tpm2_get_selftest_result(chip);
> +
>  		if (rc == TPM2_RC_TESTING)
>  			rc = TPM2_RC_SUCCESS;
>  		if (rc == TPM2_RC_INITIALIZE || rc == TPM2_RC_SUCCESS)
> -- 
> 2.13.6
>