[PATCH v5 01/11] tpm: Add support for in-kernel resetting of PCRs

[Evan Green <evgreen@chromium.org>]

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/
Co-developed-by: Matthew Garrett <mjg59@google.com>
Signed-off-by: Matthew Garrett <mjg59@google.com>
Signed-off-by: Evan Green <evgreen@chromium.org>

---

Changes in v5:
 - Change to co-developed by Matthew (Kees)

Changes in v4:
 - Open code tpm2_pcr_reset implementation in tpm-interface.c (Jarkko)
 - Rename interface symbol to tpm2_pcr_reset, fix kerneldocs (Jarkko)

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 | 47 ++++++++++++++++++++++++++++++++
 drivers/char/tpm/tpm2-cmd.c      |  7 -----
 include/linux/tpm.h              | 14 ++++++++++
 3 files changed, 61 insertions(+), 7 deletions(-)

diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index 1621ce8187052c..886277b2654e3b 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -342,6 +342,53 @@ int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
 }
 EXPORT_SYMBOL_GPL(tpm_pcr_extend);
 
+/**
+ * tpm2_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 tpm2_pcr_reset(struct tpm_chip *chip, u32 pcr_idx)
+{
+	struct tpm2_null_auth_area auth_area;
+	struct tpm_buf buf;
+	int rc;
+
+	chip = tpm_find_get_ops(chip);
+	if (!chip)
+		return -ENODEV;
+
+	if (!(chip->flags & TPM_CHIP_FLAG_TPM2)) {
+		rc = -ENOTTY;
+		goto out;
+	}
+
+	rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_PCR_RESET);
+	if (rc)
+		goto out;
+
+	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);
+
+out:
+	tpm_put_ops(chip);
+	return rc;
+}
+EXPORT_SYMBOL_GPL(tpm2_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/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index 65d03867e114c5..303ce2ea02a4b0 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -216,13 +216,6 @@ int tpm2_pcr_read(struct tpm_chip *chip, u32 pcr_idx,
 	return rc;
 }
 
-struct tpm2_null_auth_area {
-	__be32  handle;
-	__be16  nonce_size;
-	u8  attributes;
-	__be16  auth_size;
-} __packed;
-
 /**
  * tpm2_pcr_extend() - extend a PCR value
  *
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index dfeb25a0362dee..70134e6551745f 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,
@@ -293,6 +294,13 @@ struct tpm_header {
 	};
 } __packed;
 
+struct tpm2_null_auth_area {
+	__be32  handle;
+	__be16  nonce_size;
+	u8  attributes;
+	__be16  auth_size;
+} __packed;
+
 /* A string buffer type for constructing TPM commands. This is based on the
  * ideas of string buffer code in security/keys/trusted.h but is heap based
  * in order to keep the stack usage minimal.
@@ -423,6 +431,7 @@ 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 tpm2_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 +449,11 @@ static inline int tpm_pcr_read(struct tpm_chip *chip, int pcr_idx,
 	return -ENODEV;
 }
 
+static inline int tpm2_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)
 {
-- 
2.38.1.431.g37b22c650d-goog