[PATCH 03/17] tpm: Allow tpm2_start_auth_session() to start an audit session

[Matthew Garrett <matthewg@nvidia.com>]

Add an audit argument to tpm2_start_auth_session(). When set, the
session is flagged so that tpm_buf_append_hmac_session() sets
TPM2_SA_AUDIT (TPMA_SESSION_AUDIT) on every command using it, causing
the TPM to extend the session audit digest with each command and
response.

Since only a single session is held per chip, return -EBUSY if a
session is already active with a different audit setting rather than
silently reusing it.

Signed-off-by: Matthew Garrett <matthewg@nvidia.com>
---
 drivers/char/tpm/tpm2-cmd.c               |  4 +--
 drivers/char/tpm/tpm2-sessions.c          | 30 ++++++++++++++++++-----
 include/linux/tpm.h                       |  5 ++--
 security/keys/trusted-keys/trusted_tpm2.c |  6 ++---
 4 files changed, 32 insertions(+), 13 deletions(-)

diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index ae22295df798..bfad86ed0132 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -178,7 +178,7 @@ int tpm2_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
 	int i;
 
 	if (!disable_pcr_integrity) {
-		rc = tpm2_start_auth_session(chip);
+		rc = tpm2_start_auth_session(chip, false);
 		if (rc)
 			return rc;
 	}
@@ -254,7 +254,7 @@ int tpm2_get_random(struct tpm_chip *chip, u8 *dest, size_t max)
 	if (!num_bytes || max > TPM_MAX_RNG_DATA)
 		return -EINVAL;
 
-	err = tpm2_start_auth_session(chip);
+	err = tpm2_start_auth_session(chip, false);
 	if (err)
 		return err;
 
diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
index ca1e2bf424e1..9fb710a1c6c6 100644
--- a/drivers/char/tpm/tpm2-sessions.c
+++ b/drivers/char/tpm/tpm2-sessions.c
@@ -129,6 +129,8 @@ struct tpm2_auth {
 	struct aes_enckey aes_key;
 	/* saved session attributes: */
 	u8 attrs;
+	/* set TPM2_SA_AUDIT on every command using this session */
+	bool audit;
 	__be32 ordinal;
 
 	/*
@@ -376,6 +378,10 @@ void tpm_buf_append_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf,
 	/* The first write to /dev/tpm{rm0} will flush the session. */
 	attributes |= TPM2_SA_CONTINUE_SESSION;
 
+	auth = chip->auth;
+	if (auth->audit)
+		attributes |= TPM2_SA_AUDIT;
+
 	/*
 	 * The Architecture Guide requires us to strip trailing zeros
 	 * before computing the HMAC
@@ -383,7 +389,6 @@ void tpm_buf_append_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf,
 	while (passphrase && passphrase_len > 0 && passphrase[passphrase_len - 1] == '\0')
 		passphrase_len--;
 
-	auth = chip->auth;
 	auth->attrs = attributes;
 	auth->passphrase_len = passphrase_len;
 	if (passphrase_len)
@@ -777,6 +782,7 @@ int tpm_buf_check_hmac_response(struct tpm_chip *chip, struct tpm_buf *buf,
 	off_t offset_s, offset_p;
 	u8 rphash[SHA256_DIGEST_SIZE];
 	u32 attrs, cc;
+	u8 rsp_attrs;
 	struct sha256_ctx sctx;
 	struct hmac_sha256_ctx hctx;
 	u16 tag = be16_to_cpu(head->tag);
@@ -828,7 +834,7 @@ int tpm_buf_check_hmac_response(struct tpm_chip *chip, struct tpm_buf *buf,
 		goto out;
 	memcpy(auth->tpm_nonce, &buf->data[offset_s], len);
 	offset_s += len;
-	attrs = tpm_buf_read_u8(buf, &offset_s);
+	rsp_attrs = tpm_buf_read_u8(buf, &offset_s);
 	len = tpm_buf_read_u16(buf, &offset_s);
 	if (offset_s + len != tpm_buf_length(buf))
 		goto out;
@@ -854,7 +860,12 @@ int tpm_buf_check_hmac_response(struct tpm_chip *chip, struct tpm_buf *buf,
 	hmac_sha256_update(&hctx, rphash, sizeof(rphash));
 	hmac_sha256_update(&hctx, auth->tpm_nonce, sizeof(auth->tpm_nonce));
 	hmac_sha256_update(&hctx, auth->our_nonce, sizeof(auth->our_nonce));
-	hmac_sha256_update(&hctx, &auth->attrs, 1);
+	/*
+	 * The response HMAC covers the response's session attributes, which
+	 * can differ from the command's - the TPM sets auditExclusive in the
+	 * response to an exclusive audit session.
+	 */
+	hmac_sha256_update(&hctx, &rsp_attrs, 1);
 	/* we're done with the rphash, so put our idea of the hmac there */
 	hmac_sha256_final(&hctx, rphash);
 	if (crypto_memneq(rphash, &buf->data[offset_s], SHA256_DIGEST_SIZE)) {
@@ -988,13 +999,17 @@ static int tpm2_load_null(struct tpm_chip *chip, u32 *null_key)
 /**
  * tpm2_start_auth_session() - Create an a HMAC authentication session
  * @chip:	A TPM chip
+ * @audit:	Set TPM2_SA_AUDIT on every command using the session
  *
  * Loads the ephemeral key (null seed), and starts an HMAC authenticated
- * session. The null seed is flushed before the return.
+ * session. The null seed is flushed before the return. If @audit is
+ * true, the session is used as an audit session and the TPM will
+ * extend the session digest with each command and response.
  *
- * Returns zero on success, or a POSIX error code.
+ * Returns zero on success, -EBUSY if a session with a different audit
+ * setting is already active, or a POSIX error code.
  */
-int tpm2_start_auth_session(struct tpm_chip *chip)
+int tpm2_start_auth_session(struct tpm_chip *chip, bool audit)
 {
 	struct tpm_buf *buf __free(kfree) = NULL;
 	struct tpm2_auth *auth;
@@ -1002,6 +1017,8 @@ int tpm2_start_auth_session(struct tpm_chip *chip)
 	int rc;
 
 	if (chip->auth) {
+		if (chip->auth->audit != audit)
+			return -EBUSY;
 		dev_dbg_once(&chip->dev, "auth session is active\n");
 		return 0;
 	}
@@ -1009,6 +1026,7 @@ int tpm2_start_auth_session(struct tpm_chip *chip)
 	auth = kzalloc_obj(*auth);
 	if (!auth)
 		return -ENOMEM;
+	auth->audit = audit;
 
 	rc = tpm2_load_null(chip, &null_key);
 	if (rc) {
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index b6b862c3be3b..341fd5b46b2d 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -321,7 +321,7 @@ void tpm_buf_append_auth(struct tpm_chip *chip, struct tpm_buf *buf,
 
 #ifdef CONFIG_TCG_TPM2_HMAC
 
-int tpm2_start_auth_session(struct tpm_chip *chip);
+int tpm2_start_auth_session(struct tpm_chip *chip, bool audit);
 int tpm_buf_fill_hmac_session(struct tpm_chip *chip, struct tpm_buf *buf);
 int tpm_buf_check_hmac_response(struct tpm_chip *chip, struct tpm_buf *buf,
 				int rc);
@@ -329,7 +329,8 @@ void tpm2_end_auth_session(struct tpm_chip *chip);
 #else
 #include <linux/unaligned.h>
 
-static inline int tpm2_start_auth_session(struct tpm_chip *chip)
+static inline int tpm2_start_auth_session(struct tpm_chip *chip,
+					  bool audit)
 {
 	return 0;
 }
diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
index 01f18bb37047..8a15bf542a9e 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -252,7 +252,7 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
 	if (rc)
 		return rc;
 
-	rc = tpm2_start_auth_session(chip);
+	rc = tpm2_start_auth_session(chip, false);
 	if (rc)
 		goto out_put;
 
@@ -428,7 +428,7 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
 	if (blob_len > payload->blob_len)
 		return -E2BIG;
 
-	rc = tpm2_start_auth_session(chip);
+	rc = tpm2_start_auth_session(chip, false);
 	if (rc)
 		return rc;
 
@@ -492,7 +492,7 @@ static int tpm2_unseal_cmd(struct tpm_chip *chip,
 	u8 *data;
 	int rc;
 
-	rc = tpm2_start_auth_session(chip);
+	rc = tpm2_start_auth_session(chip, false);
 	if (rc)
 		return rc;
 
-- 
2.43.0