[PATCH v4 01/11] tpm: Add support for in-kernel resetting of PCRs

Evan Green
2022-11-03T18:04:53Z

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 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