[PATCH 09/17] trusted keys: Add session encryption protection to the seal/unseal path

From: James Prestwood <prestwoj@gmail.com>
To: keyrings@vger.kernel.org
Cc: James.Bottomley@HansenPartnership.com
Subject: [PATCH 09/17] trusted keys: Add session encryption protection to the seal/unseal path
Date: Mon, 18 May 2020 17:26:56 +0000	[thread overview]
Message-ID: <20200518172704.29608-10-prestwoj@gmail.com> (raw)
In-Reply-To: <20200518172704.29608-1-prestwoj@gmail.com>

From: James Bottomley <James.Bottomley@HansenPartnership.com>

If some entity is snooping the TPM bus, the can see the data going in
to be sealed and the data coming out as it is unsealed.  Add parameter
and response encryption to these cases to ensure that no secrets are
leaked even if the bus is snooped.

As part of doing this conversion it was discovered that policy
sessions can't work with HMAC protected authority because of missing
pieces (the tpm Nonce).  I've added code to work the same way as
before, which will result in potential authority exposure (while still
adding security for the command and the returned blob), and a fixme to
redo the API to get rid of this security hole.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
---
 drivers/char/tpm/tpm2-cmd.c | 124 ++++++++++++++++++++++++------------
 1 file changed, 85 insertions(+), 39 deletions(-)

diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index 92e381bfd7c8..f11906f95252 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -418,7 +418,9 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
 {
 	unsigned int blob_len;
 	struct tpm_buf buf;
+	struct tpm_buf t2b;
 	u32 hash;
+	struct tpm2_auth *auth;
 	int i;
 	int rc;
 
@@ -432,45 +434,56 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
 	if (i = ARRAY_SIZE(tpm2_hash_map))
 		return -EINVAL;
 
-	rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_CREATE);
+	rc = tpm2_start_auth_session(chip, &auth);
 	if (rc)
 		return rc;
 
-	tpm_buf_append_u32(&buf, options->keyhandle);
-	tpm2_buf_append_auth(&buf, TPM2_RS_PW,
-			     NULL /* nonce */, 0,
-			     0 /* session_attributes */,
-			     options->keyauth /* hmac */,
-			     TPM_DIGEST_SIZE);
+	rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_CREATE);
+	if (rc) {
+		tpm2_end_auth_session(auth);
+		return rc;
+	}
+
+	rc = tpm_buf_init_2b(&t2b);
+	if (rc) {
+		tpm_buf_destroy(&buf);
+		tpm2_end_auth_session(auth);
+		return rc;
+	}
 
+	tpm_buf_append_name(&buf, auth, options->keyhandle, NULL);
+	tpm_buf_append_hmac_session(&buf, auth, TPM2_SA_DECRYPT,
+				    options->keyauth, TPM_DIGEST_SIZE);
 	/* sensitive */
-	tpm_buf_append_u16(&buf, 4 + TPM_DIGEST_SIZE + payload->key_len + 1);
+	tpm_buf_append_u16(&t2b, TPM_DIGEST_SIZE);
+	tpm_buf_append(&t2b, options->blobauth, TPM_DIGEST_SIZE);
+	tpm_buf_append_u16(&t2b, payload->key_len + 1);
+	tpm_buf_append(&t2b, payload->key, payload->key_len);
+	tpm_buf_append_u8(&t2b, payload->migratable);
 
-	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(&buf, payload->key, payload->key_len);
-	tpm_buf_append_u8(&buf, payload->migratable);
+	tpm_buf_append_2b(&buf, &t2b);
 
 	/* public */
-	tpm_buf_append_u16(&buf, 14 + options->policydigest_len);
-	tpm_buf_append_u16(&buf, TPM_ALG_KEYEDHASH);
-	tpm_buf_append_u16(&buf, hash);
+	tpm_buf_append_u16(&t2b, TPM_ALG_KEYEDHASH);
+	tpm_buf_append_u16(&t2b, hash);
 
 	/* policy */
 	if (options->policydigest_len) {
-		tpm_buf_append_u32(&buf, 0);
-		tpm_buf_append_u16(&buf, options->policydigest_len);
-		tpm_buf_append(&buf, options->policydigest,
+		tpm_buf_append_u32(&t2b, 0);
+		tpm_buf_append_u16(&t2b, options->policydigest_len);
+		tpm_buf_append(&t2b, options->policydigest,
 			       options->policydigest_len);
 	} else {
-		tpm_buf_append_u32(&buf, TPM2_OA_USER_WITH_AUTH);
-		tpm_buf_append_u16(&buf, 0);
+		tpm_buf_append_u32(&t2b, TPM2_OA_USER_WITH_AUTH);
+		tpm_buf_append_u16(&t2b, 0);
 	}
 
 	/* public parameters */
-	tpm_buf_append_u16(&buf, TPM_ALG_NULL);
-	tpm_buf_append_u16(&buf, 0);
+	tpm_buf_append_u16(&t2b, TPM_ALG_NULL);
+	/* unique (zero) */
+	tpm_buf_append_u16(&t2b, 0);
+
+	tpm_buf_append_2b(&buf, &t2b);
 
 	/* outside info */
 	tpm_buf_append_u16(&buf, 0);
@@ -483,7 +496,9 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
 		goto out;
 	}
 
+	tpm_buf_fill_hmac_session(&buf, auth);
 	rc = tpm_transmit_cmd(chip, &buf, 4, "sealing data");
+	rc = tpm_buf_check_hmac_response(&buf, auth, rc);
 	if (rc)
 		goto out;
 
@@ -501,6 +516,7 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
 	payload->blob_len = blob_len;
 
 out:
+	tpm_buf_destroy(&t2b);
 	tpm_buf_destroy(&buf);
 
 	if (rc > 0) {
@@ -532,6 +548,7 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
 			 u32 *blob_handle)
 {
 	struct tpm_buf buf;
+	struct tpm2_auth *auth;
 	unsigned int private_len;
 	unsigned int public_len;
 	unsigned int blob_len;
@@ -546,17 +563,18 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
 	if (blob_len > payload->blob_len)
 		return -E2BIG;
 
-	rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_LOAD);
+	rc = tpm2_start_auth_session(chip, &auth);
 	if (rc)
 		return rc;
 
-	tpm_buf_append_u32(&buf, options->keyhandle);
-	tpm2_buf_append_auth(&buf, TPM2_RS_PW,
-			     NULL /* nonce */, 0,
-			     0 /* session_attributes */,
-			     options->keyauth /* hmac */,
-			     TPM_DIGEST_SIZE);
+	rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_LOAD);
+	if (rc) {
+		tpm2_end_auth_session(auth);
+		return rc;
+	}
 
+	tpm_buf_append_name(&buf, auth, options->keyhandle, NULL);
+	tpm_buf_append_hmac_session(&buf, auth, 0, options->keyauth, TPM_DIGEST_SIZE);
 	tpm_buf_append(&buf, payload->blob, blob_len);
 
 	if (buf.flags & TPM_BUF_OVERFLOW) {
@@ -564,7 +582,9 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
 		goto out;
 	}
 
+	tpm_buf_fill_hmac_session(&buf, auth);
 	rc = tpm_transmit_cmd(chip, &buf, 4, "loading blob");
+	rc = tpm_buf_check_hmac_response(&buf, auth, rc);
 	if (!rc)
 		*blob_handle = be32_to_cpup(
 			(__be32 *) &buf.data[TPM_HEADER_SIZE]);
@@ -596,24 +616,50 @@ static int tpm2_unseal_cmd(struct tpm_chip *chip,
 			   u32 blob_handle)
 {
 	struct tpm_buf buf;
+	struct tpm2_auth *auth;
 	u16 data_len;
 	u8 *data;
 	int rc;
 
-	rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_UNSEAL);
+	rc = tpm2_start_auth_session(chip, &auth);
 	if (rc)
 		return rc;
 
-	tpm_buf_append_u32(&buf, blob_handle);
-	tpm2_buf_append_auth(&buf,
-			     options->policyhandle ?
-			     options->policyhandle : TPM2_RS_PW,
-			     NULL /* nonce */, 0,
-			     TPM2_SA_CONTINUE_SESSION,
-			     options->blobauth /* hmac */,
-			     TPM_DIGEST_SIZE);
+	rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_UNSEAL);
+	if (rc) {
+		tpm2_end_auth_session(auth);
+		return rc;
+	}
+
+	tpm_buf_append_name(&buf, auth, blob_handle, NULL);
+
+	if (!options->policyhandle) {
+		tpm_buf_append_hmac_session(&buf, auth, TPM2_SA_ENCRYPT,
+					    options->blobauth, TPM_DIGEST_SIZE);
+	} else {
+		/*
+		 * FIXME: the policy can't be used for HMAC protection
+		 * of the authorization because it must be generated
+		 * with the initial nonces which isn't passed in, so
+		 * append a second encryption session to at least HMAC
+		 * protect the command and encrypt the sealed blob on
+		 * return.
+		 *
+		 * Note: this also means the caller either has to use
+		 * an empty password or compute the password HMAC
+		 * based on the policy nonces and place it in blobauth
+		 */
+		tpm2_buf_append_auth(&buf, options->policyhandle,
+				     NULL /* nonce */, 0, 0,
+				     options->blobauth /* hmac */,
+				     TPM_DIGEST_SIZE);
+		tpm_buf_append_hmac_session_opt(&buf, auth, TPM2_SA_ENCRYPT,
+						NULL, 0);
+	}
 
+	tpm_buf_fill_hmac_session(&buf, auth);
 	rc = tpm_transmit_cmd(chip, &buf, 6, "unsealing");
+	rc = tpm_buf_check_hmac_response(&buf, auth, rc);
 	if (rc > 0)
 		rc = -EPERM;
 
-- 
2.21.1
