[PATCH 3/3] tpm2-cmd: React correctly to RC_TESTING from self tests

[Alexander Steffen <Alexander.Steffen-d0qZbvYSIPpWk0Htik3J/w@public.gmane.org>]

The TPM can choose one of two ways to react to the TPM2_SelfTest command.
It can either run all self tests synchronously and then return RC_SUCCESS
once all tests were successful. Or it can choose to run the tests
asynchronously and return RC_TESTING immediately while the self tests still
execute in the background.

The previous implementation apparently was not aware of those possibilities
and attributed RC_TESTING to some prototype chips instead. With this change
the return code of TPM2_SelfTest is interpreted correctly, i.e. the self
test result is polled if and only if RC_TESTING is received. Unfortunately,
the polling cannot be done in the most straightforward way, so the solution
is explained with a comment in the code.

Signed-off-by: Alexander Steffen <Alexander.Steffen-d0qZbvYSIPpWk0Htik3J/w@public.gmane.org>
---
 drivers/char/tpm/tpm2-cmd.c | 68 ++++++++++++++++++---------------------------
 1 file changed, 27 insertions(+), 41 deletions(-)

diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index e3d4cc3..d09032f 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -834,68 +834,54 @@ static const struct tpm_input_header tpm2_selftest_header = {
 };
 
 /**
- * tpm2_continue_selftest() - start a self test
- *
- * @chip: TPM chip to use
- * @full: test all commands instead of testing only those that were not
- *        previously tested.
- *
- * Return: Same as with tpm_transmit_cmd with exception of RC_TESTING.
- */
-static int tpm2_start_selftest(struct tpm_chip *chip, bool full)
-{
-	int rc;
-	struct tpm2_cmd cmd;
-
-	cmd.header.in = tpm2_selftest_header;
-	cmd.params.selftest_in.full_test = full;
-
-	rc = tpm_transmit_cmd(chip, NULL, &cmd, TPM2_SELF_TEST_IN_SIZE, 0, 0,
-			      "continue selftest");
-
-	/* At least some prototype chips seem to give RC_TESTING error
-	 * immediately. This is a workaround for that.
-	 */
-	if (rc == TPM2_RC_TESTING) {
-		dev_warn(&chip->dev, "Got RC_TESTING, ignoring\n");
-		rc = 0;
-	}
-
-	return rc;
-}
-
-/**
  * tpm2_do_selftest() - ensure that all self tests have passed
  *
  * @chip: TPM chip to use
  *
  * Return: Same as with tpm_transmit_cmd.
  *
- * During the self test TPM2 commands return with the error code RC_TESTING.
- * Waiting is done by issuing PCR read until it executes successfully.
+ * The TPM can either run all self tests synchronously and then return
+ * RC_SUCCESS once all tests were successful. Or it can choose to run the tests
+ * asynchronously and return RC_TESTING immediately while the self tests still
+ * execute in the background. This function handles both cases and waits until
+ * all tests have completed.
  */
 static int tpm2_do_selftest(struct tpm_chip *chip)
 {
 	int rc;
 	unsigned int delay_msec = 20;
 	long duration;
+	struct tpm2_cmd cmd;
 
 	duration = jiffies_to_msecs(
 		tpm2_calc_ordinal_duration(chip, TPM2_CC_SELF_TEST));
 
-	rc = tpm2_start_selftest(chip, false);
-	if (rc)
-		return rc;
-
 	while (duration > 0) {
-		/* Attempt to read a PCR value */
-		rc = tpm2_pcr_read(chip, 0, NULL);
-		if (rc < 0)
-			break;
+		cmd.header.in = tpm2_selftest_header;
+		cmd.params.selftest_in.full_test = 0;
+
+		rc = tpm_transmit_cmd(chip, NULL, &cmd, TPM2_SELF_TEST_IN_SIZE,
+				      0, 0, "continue selftest");
 
 		if (rc != TPM2_RC_TESTING)
 			break;
 
+		/* If RC_TESTING is received, ideally the code should now poll
+		 * the selfTestDone bit in the STS register, as this avoids
+		 * sending more commands, that might interrupt self tests
+		 * executing in the background and thus prevent them from ever
+		 * completing.
+		 * Unfortunately, it cannot be guaranteed that this bit is
+		 * correctly implemented for all devices, so the next best thing
+		 * would be to use TPM2_GetTestResult to query the test result.
+		 * But the response to that command can be very long, and the
+		 * code currently lacks the capabilities for efficient
+		 * unmarshalling, so it is difficult to execute this command.
+		 * Therefore, we simply run the TPM2_SelfTest command in a loop,
+		 * which should complete eventually, since we only request the
+		 * execution of self tests that have not yet been done.
+		 */
+
 		msleep(delay_msec);
 		duration -= delay_msec;
 
-- 
2.7.4


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