linux-kernel - [PATCH v2] tpm: Add upgrade/reduced mode support for TPM1.2 modules

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Date:   Thu, 2 Jun 2022 18:13:01 +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 <stefan.mahnke-hartmann@...ineon.com>
Subject: [PATCH v2] 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 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 flag, which is used later during
driver initialization/deinitialization to disable functionality which
makes no sense or will fail in the current TPM state. The following
functionality is affected:
 * Do not register TPM as a hwrng
 * Do not get pcr allocation
 * Do not register sysfs entries which provide information impossible to
   obtain in limited mode

Signed-off-by: Stefan Mahnke-Hartmann <stefan.mahnke-hartmann@...ineon.com>
---
Changelog:
 * v2:
   * Commit message updated.
   * Error handling for failed self test and other errors seperated.
.
 drivers/char/tpm/tpm.h      | 1 +
 drivers/char/tpm/tpm1-cmd.c | 9 +++++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
index 2163c6ee0d36..c0778498bc41 100644
--- a/drivers/char/tpm/tpm.h
+++ b/drivers/char/tpm/tpm.h
@@ -56,6 +56,7 @@ enum tpm_addr {
 #define TPM_ERR_DEACTIVATED     0x6
 #define TPM_ERR_DISABLED        0x7
 #define TPM_ERR_INVALID_POSTINIT 38
+#define TPM_ERR_FAILEDSELFTEST  0x1C

 #define TPM_TAG_RQU_COMMAND 193

diff --git a/drivers/char/tpm/tpm1-cmd.c b/drivers/char/tpm/tpm1-cmd.c
index f7dc986fa4a0..fe21679ba0b6 100644
--- a/drivers/char/tpm/tpm1-cmd.c
+++ b/drivers/char/tpm/tpm1-cmd.c
@@ -709,8 +709,13 @@ int tpm1_auto_startup(struct tpm_chip *chip)
 	if (rc)
 		goto out;
 	rc = tpm1_do_selftest(chip);
-	if (rc) {
-		dev_err(&chip->dev, "TPM self test failed\n");
+	if (rc == TPM_ERR_FAILEDSELFTEST) {
+		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;
+		return 0;
+	} else if (rc) {
+		dev_err(&chip->dev, "TPM self test not successful\n");
 		goto out;
 	}

-- 
2.25.1