[PATCH v3 06/11] security: keys: trusted: Verify creation data

Evan Green
2022-09-27T16:51:21Z

If a loaded key contains creation data, ask the TPM to verify that
creation data. This allows users like encrypted hibernate to know that
the loaded and parsed creation data has not been tampered with.

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

---
Source material for this change is at:
https://patchwork.kernel.org/project/linux-pm/patch/20210220013255.1083202-9-matthewgarrett@google.com/

Changes in v3:
- Changed funky tag to suggested-by (Kees). Matthew, holler if you want
something different.

Changes in v2:
- Adjust hash len by 2 due to new ASN.1 storage, and add underflow
check.

include/linux/tpm.h | 1 +
security/keys/trusted-keys/trusted_tpm2.c | 77 ++++++++++++++++++++++-
2 files changed, 77 insertions(+), 1 deletion(-)

diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 8320cbac6f4009..438f8bc0a50582 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -224,6 +224,7 @@ enum tpm2_command_codes {
TPM2_CC_SELF_TEST = 0x0143,
TPM2_CC_STARTUP = 0x0144,
TPM2_CC_SHUTDOWN = 0x0145,
+ TPM2_CC_CERTIFYCREATION = 0x014A,
TPM2_CC_NV_READ = 0x014E,
TPM2_CC_CREATE = 0x0153,
TPM2_CC_LOAD = 0x0157,
diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
index a7ad83bc0e5396..c76a1b5a2e8471 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -703,6 +703,74 @@ static int tpm2_unseal_cmd(struct tpm_chip *chip,
return rc;
}

+/**
+ * tpm2_certify_creation() - execute a TPM2_CertifyCreation command
+ *
+ * @chip: TPM chip to use
+ * @payload: the key data in clear and encrypted form
+ * @blob_handle: the loaded TPM handle of the key
+ *
+ * Return: 0 on success
+ * -EINVAL on tpm error status
+ * < 0 error from tpm_send or tpm_buf_init
+ */
+static int tpm2_certify_creation(struct tpm_chip *chip,
+ struct trusted_key_payload *payload,
+ u32 blob_handle)
+{
+ struct tpm_header *head;
+ struct tpm_buf buf;
+ int rc;
+
+ rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_CERTIFYCREATION);
+ if (rc)
+ return rc;
+
+ /* Use TPM_RH_NULL for signHandle */
+ tpm_buf_append_u32(&buf, 0x40000007);
+
+ /* Object handle */
+ tpm_buf_append_u32(&buf, blob_handle);
+
+ /* Auth */
+ tpm_buf_append_u32(&buf, 9);
+ tpm_buf_append_u32(&buf, TPM2_RS_PW);
+ tpm_buf_append_u16(&buf, 0);
+ tpm_buf_append_u8(&buf, 0);
+ tpm_buf_append_u16(&buf, 0);
+
+ /* Qualifying data */
+ tpm_buf_append_u16(&buf, 0);
+
+ /* Creation data hash */
+ if (payload->creation_hash_len < 2) {
+ rc = -EINVAL;
+ goto out;
+ }
+
+ tpm_buf_append_u16(&buf, payload->creation_hash_len - 2);
+ tpm_buf_append(&buf, payload->creation_hash + 2,
+ payload->creation_hash_len - 2);
+
+ /* signature scheme */
+ tpm_buf_append_u16(&buf, TPM_ALG_NULL);
+
+ /* creation ticket */
+ tpm_buf_append(&buf, payload->tk, payload->tk_len);
+
+ rc = tpm_transmit_cmd(chip, &buf, 6, "certifying creation data");
+ if (rc)
+ goto out;
+
+ head = (struct tpm_header *)buf.data;
+
+ if (be32_to_cpu(head->return_code) != TPM2_RC_SUCCESS)
+ rc = -EINVAL;
+out:
+ tpm_buf_destroy(&buf);
+ return rc;
+}
+
/**
* tpm2_unseal_trusted() - unseal the payload of a trusted key
*
@@ -728,8 +796,15 @@ int tpm2_unseal_trusted(struct tpm_chip *chip,
goto out;

rc = tpm2_unseal_cmd(chip, payload, options, blob_handle);
- tpm2_flush_context(chip, blob_handle);
+ if (rc)
+ goto flush;
+
+ if (payload->creation_len)
+ rc = tpm2_certify_creation(chip, payload, blob_handle);

+
+flush:
+ tpm2_flush_context(chip, blob_handle);
out:
tpm_put_ops(chip);

--
2.31.0