linux-kernel - [PATCH] tpm: Add Upgrade/Reduced mode support for TPM2 modules

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Date:   Mon, 19 Jul 2021 15:37:17 +0200
From:   Borys Movchan <borysmn@...s.com>
To:     Peter Huewe <peterhuewe@....de>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Jason Gunthorpe <jgg@...pe.ca>
CC:     <kernel@...s.com>, Borys Movchan <borysmn@...s.com>,
        <linux-integrity@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] tpm: Add Upgrade/Reduced mode support for TPM2 modules

On some systems, especially embedded, TPM might start in
Upgrade/Reduced mode due to the previous failure of a firmware
upgrade process. Allow the TPM driver to handle such situations
properly. Enables a possibility for userspace application to
finalize TPM upgrade or recovery if required.

Signed-off-by: Borys Movchan <borysmn@...s.com>
---
 drivers/char/tpm/tpm-chip.c | 23 +++++++++++++++--------
 drivers/char/tpm/tpm2-cmd.c | 12 ++++++++++--
 include/linux/tpm.h         |  1 +
 3 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index ddaeceb7e109..ff2367c447fb 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -574,20 +574,25 @@ static int tpm_get_pcr_allocation(struct tpm_chip *chip)
 int tpm_chip_register(struct tpm_chip *chip)
 {
 	int rc;
+	bool limited_mode = false;
 
 	rc = tpm_chip_start(chip);
 	if (rc)
 		return rc;
 	rc = tpm_auto_startup(chip);
-	if (rc) {
+	if (rc == -EIO) {
+		limited_mode = true;
+	} else if (rc) {
 		tpm_chip_stop(chip);
 		return rc;
 	}
 
-	rc = tpm_get_pcr_allocation(chip);
-	tpm_chip_stop(chip);
-	if (rc)
-		return rc;
+	if (!limited_mode) {
+		rc = tpm_get_pcr_allocation(chip);
+		tpm_chip_stop(chip);
+		if (rc)
+			return rc;
+	}
 
 	tpm_sysfs_add_device(chip);
 
@@ -595,9 +600,11 @@ int tpm_chip_register(struct tpm_chip *chip)
 
 	tpm_add_ppi(chip);
 
-	rc = tpm_add_hwrng(chip);
-	if (rc)
-		goto out_ppi;
+	if (!limited_mode) {
+		rc = tpm_add_hwrng(chip);
+		if (rc)
+			goto out_ppi;
+	}
 
 	rc = tpm_add_char_device(chip);
 	if (rc)
diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index a25815a6f625..7468353ed67d 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -718,7 +718,8 @@ static int tpm2_startup(struct tpm_chip *chip)
  *                     sequence
  * @chip: TPM chip to use
  *
- * Returns 0 on success, < 0 in case of fatal error.
+ * Returns 0 on success, -ENODEV in case of fatal error,
+ *	    -EIO in case of Reduced/Upgrade mode
  */
 int tpm2_auto_startup(struct tpm_chip *chip)
 {
@@ -729,7 +730,10 @@ int tpm2_auto_startup(struct tpm_chip *chip)
 		goto out;
 
 	rc = tpm2_do_selftest(chip);
-	if (rc && rc != TPM2_RC_INITIALIZE)
+	if (rc == TPM2_RC_UPGRADE) {
+		rc = -EIO;
+		goto out;
+	} else if (rc && rc != TPM2_RC_INITIALIZE)
 		goto out;
 
 	if (rc == TPM2_RC_INITIALIZE) {
@@ -743,6 +747,10 @@ int tpm2_auto_startup(struct tpm_chip *chip)
 	}
 
 	rc = tpm2_get_cc_attrs_tbl(chip);
+	if (rc) { /* Succeeded until here, but failed -> reduced mode */
+		rc = -EIO;
+		goto out;
+	}
 
 out:
 	if (rc > 0)
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index aa11fe323c56..e873c42907f0 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -207,6 +207,7 @@ enum tpm2_return_codes {
 	TPM2_RC_INITIALIZE	= 0x0100, /* RC_VER1 */
 	TPM2_RC_FAILURE		= 0x0101,
 	TPM2_RC_DISABLED	= 0x0120,
+	TPM2_RC_UPGRADE		= 0x012D,
 	TPM2_RC_COMMAND_CODE    = 0x0143,
 	TPM2_RC_TESTING		= 0x090A, /* RC_WARN */
 	TPM2_RC_REFERENCE_H0	= 0x0910,
-- 
2.20.1