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

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.

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 <redacted>
Tested-by: Mimi Zohar <redacted> (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
+ *
+ * @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.
+ */
+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 */
+		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

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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.

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

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

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