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From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: linux-integrity@vger.kernel.org
Cc: Mimi Zohar <zohar@linux.ibm.com>,
	Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Subject: [PATCH 5/8] security: keys: trusted: Make sealed key properly interoperable
Date: Sat, 07 Dec 2019 21:11:28 -0800
Message-ID: <1575781888.14069.14.camel@HansenPartnership.com> (raw)
In-Reply-To: <1575781600.14069.8.camel@HansenPartnership.com>

The current implementation appends a migratable flag to the end of a
key, meaning the format isn't exactly interoperable because the using
party needs to know to strip this extra byte.  However, all other
consumers of TPM sealed blobs expect the unseal to return exactly the
key.  Since TPM2 keys have a key property flag that corresponds to
migratable, use that flag instead and make the actual key the only
sealed quantity.  This is secure because the key properties are bound
to a hash in the private part, so if they're altered the key won't
load.

Backwards compatibility is implemented by detecting whether we're
loading a new format key or not and correctly setting migratable from
the last byte of old format keys.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
---
 include/keys/trusted-type.h               |  1 +
 include/linux/tpm.h                       |  2 ++
 security/keys/trusted-keys/trusted_tpm2.c | 57 ++++++++++++++++++++++---------
 3 files changed, 44 insertions(+), 16 deletions(-)

diff --git a/include/keys/trusted-type.h b/include/keys/trusted-type.h
index a94c03a61d8f..4728e13aada8 100644
--- a/include/keys/trusted-type.h
+++ b/include/keys/trusted-type.h
@@ -22,6 +22,7 @@ struct trusted_key_payload {
 	unsigned int key_len;
 	unsigned int blob_len;
 	unsigned char migratable;
+	unsigned char old_format;
 	unsigned char key[MAX_KEY_SIZE + 1];
 	unsigned char blob[MAX_BLOB_SIZE];
 };
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 03e9b184411b..cd46ab27baa5 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -297,6 +297,8 @@ struct tpm_buf {
 };
 
 enum tpm2_object_attributes {
+	TPM2_OA_FIXED_TPM		= BIT(1),
+	TPM2_OA_FIXED_PARENT		= BIT(4),
 	TPM2_OA_USER_WITH_AUTH		= BIT(6),
 };
 
diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
index 4efc7b64d1cd..a34ab6f90f76 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -207,6 +207,7 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
 	unsigned int blob_len;
 	struct tpm_buf buf;
 	u32 hash;
+	u32 flags;
 	int i;
 	int rc;
 
@@ -235,29 +236,30 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
 			     TPM_DIGEST_SIZE);
 
 	/* sensitive */
-	tpm_buf_append_u16(&buf, 4 + TPM_DIGEST_SIZE + payload->key_len + 1);
+	tpm_buf_append_u16(&buf, 4 + TPM_DIGEST_SIZE + payload->key_len);
 
 	tpm_buf_append_u16(&buf, TPM_DIGEST_SIZE);
 	tpm_buf_append(&buf, options->blobauth, TPM_DIGEST_SIZE);
-	tpm_buf_append_u16(&buf, payload->key_len + 1);
+	tpm_buf_append_u16(&buf, payload->key_len);
 	tpm_buf_append(&buf, payload->key, payload->key_len);
-	tpm_buf_append_u8(&buf, payload->migratable);
 
 	/* public */
 	tpm_buf_append_u16(&buf, 14 + options->policydigest_len);
 	tpm_buf_append_u16(&buf, TPM_ALG_KEYEDHASH);
 	tpm_buf_append_u16(&buf, hash);
 
+	/* key properties */
+	flags = 0;
+	flags |= options->policydigest_len ? 0 : TPM2_OA_USER_WITH_AUTH;
+	flags |= payload->migratable ? (TPM2_OA_FIXED_TPM |
+					TPM2_OA_FIXED_PARENT) : 0;
+	tpm_buf_append_u32(&buf, flags);
+
 	/* policy */
-	if (options->policydigest_len) {
-		tpm_buf_append_u32(&buf, 0);
-		tpm_buf_append_u16(&buf, options->policydigest_len);
+	tpm_buf_append_u16(&buf, options->policydigest_len);
+	if (options->policydigest_len)
 		tpm_buf_append(&buf, options->policydigest,
 			       options->policydigest_len);
-	} else {
-		tpm_buf_append_u32(&buf, TPM2_OA_USER_WITH_AUTH);
-		tpm_buf_append_u16(&buf, 0);
-	}
 
 	/* public parameters */
 	tpm_buf_append_u16(&buf, TPM_ALG_NULL);
@@ -330,13 +332,16 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
 	unsigned int private_len;
 	unsigned int public_len;
 	unsigned int blob_len;
-	u8 *blob;
+	u8 *blob, *pub;
 	int rc;
+	u32 attrs;
 
 	rc = tpm2_key_decode(payload, options, &blob);
-	if (rc)
+	if (rc) {
 		/* old form */
 		blob = payload->blob;
+		payload->old_format = 1;
+	}
 
 	/* new format carries keyhandle but old format doesn't */
 	if (!options->keyhandle)
@@ -347,6 +352,16 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
 		return -E2BIG;
 
 	public_len = be16_to_cpup((__be16 *) &blob[2 + private_len]);
+
+	pub = blob + 2 + private_len + 2;
+	/* key attributes are always at offset 4 */
+	attrs = get_unaligned_be32(pub + 4);
+	if ((attrs & (TPM2_OA_FIXED_TPM | TPM2_OA_FIXED_PARENT)) ==
+	    (TPM2_OA_FIXED_TPM | TPM2_OA_FIXED_PARENT))
+		payload->migratable = 0;
+	else
+		payload->migratable = 1;
+
 	blob_len = private_len + public_len + 4;
 	if (blob_len > payload->blob_len)
 		return -E2BIG;
@@ -427,7 +442,7 @@ static int tpm2_unseal_cmd(struct tpm_chip *chip,
 	if (!rc) {
 		data_len = be16_to_cpup(
 			(__be16 *) &buf.data[TPM_HEADER_SIZE + 4]);
-		if (data_len < MIN_KEY_SIZE ||  data_len > MAX_KEY_SIZE + 1) {
+		if (data_len < MIN_KEY_SIZE ||  data_len > MAX_KEY_SIZE) {
 			rc = -EFAULT;
 			goto out;
 		}
@@ -438,9 +453,19 @@ static int tpm2_unseal_cmd(struct tpm_chip *chip,
 		}
 		data = &buf.data[TPM_HEADER_SIZE + 6];
 
-		memcpy(payload->key, data, data_len - 1);
-		payload->key_len = data_len - 1;
-		payload->migratable = data[data_len - 1];
+		if (payload->old_format) {
+			/* migratable flag is at the end of the key */
+			memcpy(payload->key, data, data_len - 1);
+			payload->key_len = data_len - 1;
+			payload->migratable = data[data_len - 1];
+		} else {
+			/*
+			 * migratable flag already collected from key
+			 * attributes
+			 */
+			memcpy(payload->key, data, data_len);
+			payload->key_len = data_len;
+		}
 	}
 
 out:
-- 
2.16.4


  parent reply index

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-08  5:06 [PATCH 0/8] Fix TPM 2.0 trusted keys James Bottomley
2019-12-08  5:07 ` [PATCH 1/8] security: keys: trusted: flush the key handle after use James Bottomley
2019-12-09  8:31   ` David Woodhouse
2019-12-09 15:38     ` James Bottomley
2019-12-08  5:08 ` [PATCH 2/8] lib: add asn.1 encoder James Bottomley
2019-12-09  8:50   ` David Woodhouse
2019-12-09 15:46     ` James Bottomley
2019-12-09 22:05   ` Matthew Garrett
2019-12-09 22:43     ` James Bottomley
2019-12-08  5:09 ` [PATCH 3/8] oid_registry: Add TCG defined OIDS for TPM keys James Bottomley
2019-12-09  8:55   ` David Woodhouse
2019-12-09 16:21     ` James Bottomley
2020-06-19 20:45     ` Wiseman, Monty (GE Research, US)
2020-06-19 22:50       ` Jerry Snitselaar
2020-06-20 15:36       ` James Bottomley
2020-06-23  1:17       ` Jarkko Sakkinen
2019-12-08  5:10 ` [PATCH 4/8] security: keys: trusted: use ASN.1 tpm2 key format for the blobs James Bottomley
2019-12-09 10:04   ` David Woodhouse
2019-12-09 16:31     ` James Bottomley
2019-12-08  5:11 ` James Bottomley [this message]
2019-12-09 10:09   ` [PATCH 5/8] security: keys: trusted: Make sealed key properly interoperable David Woodhouse
2019-12-09 17:23     ` James Bottomley
2019-12-08  5:12 ` [PATCH 6/8] security: keys: trusted: add PCR policy to TPM2 keys James Bottomley
2019-12-09 10:18   ` David Woodhouse
2019-12-09 18:03     ` James Bottomley
2019-12-09 18:44       ` David Woodhouse
2019-12-09 19:11         ` James Bottomley
2019-12-25 17:08           ` Ken Goldman
2019-12-08  5:13 ` [PATCH 7/8] security: keys: trusted: add ability to specify arbitrary policy James Bottomley
2019-12-08  5:14 ` [PATCH 8/8] security: keys: trusted: implement counter/timer policy James Bottomley
2019-12-09 20:20 ` [PATCH 0/8] Fix TPM 2.0 trusted keys Jarkko Sakkinen
2019-12-09 20:57   ` James Bottomley

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