linux-kernel - [PATCH] tpm: Add upgrade/reduced mode support for TPM1.2 modules

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Message-ID: <20220601083810.330809-1-stefan.mahnke-hartmann@infineon.com>
Date:   Wed, 1 Jun 2022 10:38:11 +0200
From:   Stefan Mahnke-Hartmann <stefan.mahnke-hartmann@...ineon.com>
To:     <jarkko@...nel.org>, <linux-integrity@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <peterhuewe@....de>, <jgg@...pe.ca>,
        <stefan.mahnke-hartmann@...ineon.com>
Subject: [PATCH] tpm: Add upgrade/reduced mode support for TPM1.2 modules

In case a TPM in failure mode is detected, the TPM should be accessible
through a transparent communication channel for analysing purposes (e.g.
TPM_GetTestResult) or a field upgrade. Since a TPM in failure mode has
similar reduced functionality as in field upgrade mode, the flag
TPM_CHIP_FLAG_FIRMWARE_UPGRADE_MODE is also valid.

As described in TCG TPM Main Part1 Design Principles, Revision 116,
chapter 9.2.1. the TPM also allows an update function in case a TPM is
in failure mode.

If the TPM in failure mode is detected, the function tpm1_auto_startup()
sets TPM_CHIP_FLAG_FIRMWARE_UPGRADE_MODE flag. This patch simply follows
the same rationale as TPM2 in field upgrade mode.

Signed-off-by: Stefan Mahnke-Hartmann <stefan.mahnke-hartmann@...ineon.com>
---
If you have any better suggestions, please let me know.

 drivers/char/tpm/tpm1-cmd.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/char/tpm/tpm1-cmd.c b/drivers/char/tpm/tpm1-cmd.c
index f7dc986fa4a0..7a42d74c450c 100644
--- a/drivers/char/tpm/tpm1-cmd.c
+++ b/drivers/char/tpm/tpm1-cmd.c
@@ -710,8 +710,10 @@ int tpm1_auto_startup(struct tpm_chip *chip)
 		goto out;
 	rc = tpm1_do_selftest(chip);
 	if (rc) {
-		dev_err(&chip->dev, "TPM self test failed\n");
-		goto out;
+		dev_err(&chip->dev, "TPM self test failed, so the TPM has limited functionality\n");
+		/* A TPM in this state possibly allows or needs a firmware upgrade */
+		chip->flags |= TPM_CHIP_FLAG_FIRMWARE_UPGRADE;
+		rc = 0;
 	}

 	return rc;
-- 
2.25.1