[PATCH 3/9] security: keys: trusted: Parse out individual components of the key blob

From: Matthew Garrett <matthewgarrett@google.com>
To: linux-kernel@vger.kernel.org
Cc: linux-integrity@vger.kernel.org, linux-pm@vger.kernel.org,
	keyrings@vger.kernel.org, zohar@linux.ibm.com,
	jejb@linux.ibm.com, jarkko@kernel.org, corbet@lwn.net,
	rjw@rjwysocki.net, Matthew Garrett <matthewgarrett@google.com>,
	Matthew Garrett <mjg59@google.com>
Subject: [PATCH 3/9] security: keys: trusted: Parse out individual components of the key blob
Date: Sat, 20 Feb 2021 01:32:49 +0000	[thread overview]
Message-ID: <20210220013255.1083202-4-matthewgarrett@google.com> (raw)
In-Reply-To: <20210220013255.1083202-1-matthewgarrett@google.com>

Performing any sort of state validation of a sealed TPM blob requires
being able to access the individual members in the response. Parse the
blob sufficiently to be able to stash pointers to each member, along
with the length.

Signed-off-by: Matthew Garrett <mjg59@google.com>
---
 include/keys/trusted-type.h               |  8 +++
 security/keys/trusted-keys/trusted_tpm2.c | 67 ++++++++++++++++++++++-
 2 files changed, 73 insertions(+), 2 deletions(-)

diff --git a/include/keys/trusted-type.h b/include/keys/trusted-type.h
index a94c03a61d8f..020e01a99ea4 100644
--- a/include/keys/trusted-type.h
+++ b/include/keys/trusted-type.h
@@ -16,14 +16,22 @@
 #define MAX_BLOB_SIZE			512
 #define MAX_PCRINFO_SIZE		64
 #define MAX_DIGEST_SIZE			64
+#define MAX_CREATION_DATA		412
+#define MAX_TK				76
 
 struct trusted_key_payload {
 	struct rcu_head rcu;
 	unsigned int key_len;
 	unsigned int blob_len;
+	unsigned int creation_len;
+	unsigned int creation_hash_len;
+	unsigned int tk_len;
 	unsigned char migratable;
 	unsigned char key[MAX_KEY_SIZE + 1];
 	unsigned char blob[MAX_BLOB_SIZE];
+	unsigned char *creation;
+	unsigned char *creation_hash;
+	unsigned char *tk;
 };
 
 struct trusted_key_options {
diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
index 08ec7f48f01d..6357a51a24e9 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -50,6 +50,63 @@ static void tpm2_buf_append_auth(struct tpm_buf *buf, u32 session_handle,
 		tpm_buf_append(buf, hmac, hmac_len);
 }
 
+static int tpm2_unpack_blob(struct trusted_key_payload *payload)
+{
+	int tmp, offset;
+
+	/* Find the length of the private data */
+	tmp = be16_to_cpup((__be16 *) &payload->blob[0]);
+	offset = tmp + 2;
+	if (offset > payload->blob_len)
+		return -EFAULT;
+
+	/* Find the length of the public data */
+	tmp = be16_to_cpup((__be16 *) &payload->blob[offset]);
+	offset += tmp + 2;
+	if (offset > payload->blob_len)
+		return -EFAULT;
+
+	/* Find the length of the creation data and store it */
+	tmp = be16_to_cpup((__be16 *) &payload->blob[offset]);
+	if (tmp > MAX_CREATION_DATA)
+		return -E2BIG;
+
+	if ((offset + tmp + 2) > payload->blob_len)
+		return -EFAULT;
+
+	payload->creation = &payload->blob[offset + 2];
+	payload->creation_len = tmp;
+	offset += tmp + 2;
+
+	/* Find the length of the creation hash and store it */
+	tmp = be16_to_cpup((__be16 *) &payload->blob[offset]);
+	if (tmp > MAX_DIGEST_SIZE)
+		return -E2BIG;
+
+	if ((offset + tmp + 2) > payload->blob_len)
+		return -EFAULT;
+
+	payload->creation_hash = &payload->blob[offset + 2];
+	payload->creation_hash_len = tmp;
+	offset += tmp + 2;
+
+	/*
+	 * Store the creation ticket. TPMT_TK_CREATION is two bytes of tag,
+	 * four bytes of handle, and then the digest length and digest data
+	 */
+	tmp = be16_to_cpup((__be16 *) &payload->blob[offset + 6]);
+	if (tmp > MAX_TK)
+		return -E2BIG;
+
+	if ((offset + tmp + 8) > payload->blob_len)
+		return -EFAULT;
+
+	payload->tk = &payload->blob[offset];
+	payload->tk_len = tmp + 8;
+
+	return 0;
+}
+
 /**
  * tpm2_seal_trusted() - seal the payload of a trusted key
  *
@@ -64,6 +121,7 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
 		      struct trusted_key_options *options)
 {
 	unsigned int blob_len;
+	unsigned int offset;
 	struct tpm_buf buf;
 	u32 hash;
 	int i;
@@ -139,14 +197,16 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
 		rc = -E2BIG;
 		goto out;
 	}
-	if (tpm_buf_length(&buf) < TPM_HEADER_SIZE + 4 + blob_len) {
+	offset = TPM_HEADER_SIZE + 4;
+	if (tpm_buf_length(&buf) < offset + blob_len) {
 		rc = -EFAULT;
 		goto out;
 	}
 
-	memcpy(payload->blob, &buf.data[TPM_HEADER_SIZE + 4], blob_len);
+	memcpy(payload->blob, &buf.data[offset], blob_len);
 	payload->blob_len = blob_len;
 
+	rc = tpm2_unpack_blob(payload);
 out:
 	tpm_buf_destroy(&buf);
 
@@ -215,7 +275,10 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
 	if (!rc)
 		*blob_handle = be32_to_cpup(
 			(__be32 *) &buf.data[TPM_HEADER_SIZE]);
+	else
+		goto out;
 
+	rc = tpm2_unpack_blob(payload);
 out:
 	tpm_buf_destroy(&buf);
 
-- 
2.30.0.617.g56c4b15f3c-goog

