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

Evan Green
2022-09-27T16:50:21Z

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