[PATCH v3 01/11] tpm: Add support for in-kernel resetting of PCRs

[Evan Green <evgreen@chromium.org>]

From: Matthew Garrett <matthewgarrett@google.com>

Add an internal command for resetting a PCR. This will be used by the
encrypted hibernation code to set PCR23 to a known value. The
hibernation code will seal the hibernation key with a policy specifying
PCR23 be set to this known value as a mechanism to ensure that the
hibernation key is genuine. But to do this repeatedly, resetting the PCR
is necessary as well.

Link: https://lore.kernel.org/lkml/20210220013255.1083202-2-matthewgarrett@google.com/
Signed-off-by: Matthew Garrett <mjg59@google.com>
Signed-off-by: Evan Green <evgreen@chromium.org>
---

Changes in v3:
 - Unify tpm1/2_pcr_reset prototypes (Jarkko)
 - Wait no, remove the TPM1 stuff altogether (Jarkko)
 - Remove extra From tag and blank in commit msg (Jarkko).

 drivers/char/tpm/tpm-interface.c | 25 ++++++++++++++++++++++
 drivers/char/tpm/tpm.h           |  1 +
 drivers/char/tpm/tpm2-cmd.c      | 36 ++++++++++++++++++++++++++++++++
 include/linux/tpm.h              |  7 +++++++
 4 files changed, 69 insertions(+)

diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index 1621ce8187052c..2ac9079860b1e0 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -342,6 +342,31 @@ int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
 }
 EXPORT_SYMBOL_GPL(tpm_pcr_extend);
 
+/**
+ * tpm_pcr_reset - reset the specified PCR
+ * @chip:	a &struct tpm_chip instance, %NULL for the default chip
+ * @pcr_idx:	the PCR to be reset
+ *
+ * Return: same as with tpm_transmit_cmd(), or ENOTTY for TPM1 devices.
+ */
+int tpm_pcr_reset(struct tpm_chip *chip, u32 pcr_idx)
+{
+	int rc;
+
+	chip = tpm_find_get_ops(chip);
+	if (!chip)
+		return -ENODEV;
+
+	if (chip->flags & TPM_CHIP_FLAG_TPM2)
+		rc = tpm2_pcr_reset(chip, pcr_idx);
+	else
+		rc = -ENOTTY;
+
+	tpm_put_ops(chip);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(tpm_pcr_reset);
+
 /**
  * tpm_send - send a TPM command
  * @chip:	a &struct tpm_chip instance, %NULL for the default chip
diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
index 24ee4e1cc452a0..34e20b3192f833 100644
--- a/drivers/char/tpm/tpm.h
+++ b/drivers/char/tpm/tpm.h
@@ -217,6 +217,7 @@ int tpm2_pcr_read(struct tpm_chip *chip, u32 pcr_idx,
 		  struct tpm_digest *digest, u16 *digest_size_ptr);
 int tpm2_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
 		    struct tpm_digest *digests);
+int tpm2_pcr_reset(struct tpm_chip *chip, u32 pcr_idx);
 int tpm2_get_random(struct tpm_chip *chip, u8 *dest, size_t max);
 ssize_t tpm2_get_tpm_pt(struct tpm_chip *chip, u32 property_id,
 			u32 *value, const char *desc);
diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index 65d03867e114c5..69126a6770386e 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -269,6 +269,42 @@ int tpm2_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
 	return rc;
 }
 
+/**
+ * tpm2_pcr_reset() - reset a PCR
+ *
+ * @chip:	TPM chip to use.
+ * @pcr_idx:	index of the PCR.
+ *
+ * Return: Same as with tpm_transmit_cmd.
+ */
+int tpm2_pcr_reset(struct tpm_chip *chip, u32 pcr_idx)
+{
+	struct tpm_buf buf;
+	struct tpm2_null_auth_area auth_area;
+	int rc;
+
+	rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_PCR_RESET);
+	if (rc)
+		return rc;
+
+	tpm_buf_append_u32(&buf, pcr_idx);
+
+	auth_area.handle = cpu_to_be32(TPM2_RS_PW);
+	auth_area.nonce_size = 0;
+	auth_area.attributes = 0;
+	auth_area.auth_size = 0;
+
+	tpm_buf_append_u32(&buf, sizeof(struct tpm2_null_auth_area));
+	tpm_buf_append(&buf, (const unsigned char *)&auth_area,
+		       sizeof(auth_area));
+
+	rc = tpm_transmit_cmd(chip, &buf, 0, "attempting to reset a PCR");
+
+	tpm_buf_destroy(&buf);
+
+	return rc;
+}
+
 struct tpm2_get_random_out {
 	__be16 size;
 	u8 buffer[TPM_MAX_RNG_DATA];
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index dfeb25a0362dee..8320cbac6f4009 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -219,6 +219,7 @@ enum tpm2_command_codes {
 	TPM2_CC_HIERARCHY_CONTROL       = 0x0121,
 	TPM2_CC_HIERARCHY_CHANGE_AUTH   = 0x0129,
 	TPM2_CC_CREATE_PRIMARY          = 0x0131,
+	TPM2_CC_PCR_RESET		= 0x013D,
 	TPM2_CC_SEQUENCE_COMPLETE       = 0x013E,
 	TPM2_CC_SELF_TEST	        = 0x0143,
 	TPM2_CC_STARTUP		        = 0x0144,
@@ -423,6 +424,7 @@ extern ssize_t tpm_transmit_cmd(struct tpm_chip *chip, struct tpm_buf *buf,
 				size_t min_rsp_body_length, const char *desc);
 extern int tpm_pcr_read(struct tpm_chip *chip, u32 pcr_idx,
 			struct tpm_digest *digest);
+extern int tpm_pcr_reset(struct tpm_chip *chip, u32 pcr_idx);
 extern int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
 			  struct tpm_digest *digests);
 extern int tpm_send(struct tpm_chip *chip, void *cmd, size_t buflen);
@@ -440,6 +442,11 @@ static inline int tpm_pcr_read(struct tpm_chip *chip, int pcr_idx,
 	return -ENODEV;
 }
 
+static inline int tpm_pcr_reset(struct tpm_chip *chip, int pcr_idx)
+{
+	return -ENODEV;
+}
+
 static inline int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
 				 struct tpm_digest *digests)
 {
-- 
2.31.0