diff mbox series

[v2,09/11] KEYS: trusted: Add session encryption protection to the seal/unseal path

Message ID 20230124175516.5984-10-James.Bottomley@HansenPartnership.com (mailing list archive)
State New
Headers show
Series add integrity and security to TPM2 transactions | expand

Commit Message

James Bottomley Jan. 24, 2023, 5:55 p.m. UTC
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>

---

v2: fix unseal with policy and password
---
 security/keys/trusted-keys/trusted_tpm2.c | 85 ++++++++++++++++-------
 1 file changed, 61 insertions(+), 24 deletions(-)

Comments

Ben Boeckel Jan. 29, 2023, 1:06 p.m. UTC | #1
On Tue, Jan 24, 2023 at 12:55:14 -0500, James Bottomley wrote:
> If some entity is snooping the TPM bus, the can see the data going in
                                          ^^^ they
> 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.

--Ben
diff mbox series

Patch

diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
index 2b2c8eb258d5..0ed308d400da 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -230,6 +230,7 @@  int tpm2_seal_trusted(struct tpm_chip *chip,
 {
 	int blob_len = 0;
 	struct tpm_buf buf;
+	struct tpm2_auth *auth;
 	u32 hash;
 	u32 flags;
 	int i;
@@ -252,18 +253,19 @@  int tpm2_seal_trusted(struct tpm_chip *chip,
 	if (rc)
 		return rc;
 
+	rc = tpm2_start_auth_session(chip, &auth);
+	if (rc)
+		goto out_put;
+
 	rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_CREATE);
 	if (rc) {
-		tpm_put_ops(chip);
-		return rc;
+		tpm2_end_auth_session(auth);
+		goto out_put;
 	}
 
-	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);
+	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 + options->blobauth_len + payload->key_len);
@@ -308,7 +310,11 @@  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");
+	if (rc)
+		goto out;
+	rc = tpm_buf_check_hmac_response(&buf, auth, rc);
 	if (rc)
 		goto out;
 
@@ -340,6 +346,7 @@  int tpm2_seal_trusted(struct tpm_chip *chip,
 	else
 		payload->blob_len = blob_len;
 
+out_put:
 	tpm_put_ops(chip);
 	return rc;
 }
@@ -363,6 +370,7 @@  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;
@@ -409,16 +417,19 @@  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, blob, blob_len);
 
@@ -427,7 +438,9 @@  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]);
@@ -461,24 +474,48 @@  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 */,
-			     options->blobauth_len);
+	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 session was generated outside the
+		 * kernel so we don't known the nonce and thus can't
+		 * calculate a HMAC on it.  Therefore, the user can
+		 * only really use TPM2_PolicyPassword and we must
+		 * send down the plain text password, which could be
+		 * intercepted.  We can still encrypt the returned
+		 * key, but that's small comfort since the interposer
+		 * could repeat our actions with the exfiltrated
+		 * password.
+		 */
+		tpm2_buf_append_auth(&buf, options->policyhandle,
+				     NULL /* nonce */, 0, 0,
+				     options->blobauth, options->blobauth_len);
+		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;