tpm: lazy flush for the session null key

index 44f60730cff4..6cc1ea81c57c 100644
@@ -1,71 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
-
 /*
  * Copyright (C) 2018 [email protected]
- *
- * Cryptographic helper routines for handling TPM2 sessions for
- * authorization HMAC and request response encryption.
- *
- * The idea is to ensure that every TPM command is HMAC protected by a
- * session, meaning in-flight tampering would be detected and in
- * addition all sensitive inputs and responses should be encrypted.
- *
- * The basic way this works is to use a TPM feature called salted
- * sessions where a random secret used in session construction is
- * encrypted to the public part of a known TPM key.  The problem is we
- * have no known keys, so initially a primary Elliptic Curve key is
- * derived from the NULL seed (we use EC because most TPMs generate
- * these keys much faster than RSA ones).  The curve used is NIST_P256
- * because that's now mandated to be present in 'TCG TPM v2.0
- * Provisioning Guidance'
- *
- * Threat problems: the initial TPM2_CreatePrimary is not (and cannot
- * be) session protected, so a clever Man in the Middle could return a
- * public key they control to this command and from there intercept
- * and decode all subsequent session based transactions.  The kernel
- * cannot mitigate this threat but, after boot, userspace can get
- * proof this has not happened by asking the TPM to certify the NULL
- * key.  This certification would chain back to the TPM Endorsement
- * Certificate and prove the NULL seed primary had not been tampered
- * with and thus all sessions must have been cryptographically secure.
- * To assist with this, the initial NULL seed public key name is made
- * available in a sysfs file.
- *
- * Use of these functions:
- *
- * The design is all the crypto, hash and hmac gunk is confined in this
- * file and never needs to be seen even by the kernel internal user.  To
- * the user there's an init function tpm2_sessions_init() that needs to
- * be called once per TPM which generates the NULL seed primary key.
- *
- * These are the usage functions:
- *
- * tpm2_start_auth_session() which allocates the opaque auth structure
- *	and gets a session from the TPM.  This must be called before
- *	any of the following functions.  The session is protected by a
- *	session_key which is derived from a random salt value
- *	encrypted to the NULL seed.
- * tpm2_end_auth_session() kills the session and frees the resources.
- *	Under normal operation this function is done by
- *	tpm_buf_check_hmac_response(), so this is only to be used on
- *	error legs where the latter is not executed.
- * tpm_buf_append_name() to add a handle to the buffer.  This must be
- *	used in place of the usual tpm_buf_append_u32() for adding
- *	handles because handles have to be processed specially when
- *	calculating the HMAC.  In particular, for NV, volatile and
- *	permanent objects you now need to provide the name.
- * tpm_buf_append_hmac_session() which appends the hmac session to the
- *	buf in the same way tpm_buf_append_auth does().
- * tpm_buf_fill_hmac_session() This calculates the correct hash and
- *	places it in the buffer.  It must be called after the complete
- *	command buffer is finalized so it can fill in the correct HMAC
- *	based on the parameters.
- * tpm_buf_check_hmac_response() which checks the session response in
- *	the buffer and calculates what it should be.  If there's a
- *	mismatch it will log a warning and return an error.  If
- *	tpm_buf_append_hmac_session() did not specify
- *	TPM_SA_CONTINUE_SESSION then the session will be closed (if it
- *	hasn't been consumed) and the auth structure freed.
  */
 
 #include "tpm.h"

index 6cc1ea81c57c..d63510ad44ab 100644
@@ -1288,8 +1288,10 @@ int tpm2_sessions_init(struct tpm_chip *chip)
 	int rc;
 
 	rc = tpm2_create_null_primary(chip);
-	if (rc)
+	if (rc) {
 		dev_err(&chip->dev, "TPM: security failed (NULL seed derivation): %d\n", rc);
+		return rc;
+	}
 
 	chip->auth = kmalloc(sizeof(*chip->auth), GFP_KERNEL);
 	if (!chip->auth)

index d63510ad44ab..34ce0d9d4577 100644
@@ -850,9 +850,10 @@ static int tpm2_parse_start_auth_session(struct tpm2_auth *auth,
 
 static int tpm2_load_null(struct tpm_chip *chip, u32 *null_key)
 {
-	int rc;
 	unsigned int offset = 0; /* dummy offset for null seed context */
 	u8 name[SHA256_DIGEST_SIZE + 2];
+	u32 tmp_null_key;
+	int rc;
 
 	rc = tpm2_load_context(chip, chip->null_key_context, &offset,
 			       null_key);

@@ -861,11 +862,17 @@ static int tpm2_load_null(struct tpm_chip *chip, u32 *null_key)
 
 	/* an integrity failure may mean the TPM has been reset */
 	dev_err(&chip->dev, "NULL key integrity failure!\n");
-	/* check the null name against what we know */
-	tpm2_create_primary(chip, TPM2_RH_NULL, NULL, name);
-	if (memcmp(name, chip->null_key_name, sizeof(name)) == 0)
-		/* name unchanged, assume transient integrity failure */
+
+	rc = tpm2_create_primary(chip, TPM2_RH_NULL, &tmp_null_key, name);
+	if (rc)
 		return rc;
+
+	/* Return the null key if the name has not been changed: */
+	if (memcmp(name, chip->null_key_name, sizeof(name)) == 0) {
+		*null_key = tmp_null_key;
+		return 0;
+	}
+
 	/*
 	 * Fatal TPM failure: the NULL seed has actually changed, so
 	 * the TPM must have been illegally reset.  All in-kernel TPM

@@ -874,6 +881,7 @@ static int tpm2_load_null(struct tpm_chip *chip, u32 *null_key)
 	 * userspace programmes can't be compromised by it.
 	 */
 	dev_err(&chip->dev, "NULL name has changed, disabling TPM due to interference\n");
+	tpm2_flush_context(chip, tmp_null_key);
 	chip->flags |= TPM_CHIP_FLAG_DISABLE;
 
 	return rc;

@@ -991,10 +999,6 @@ static int tpm2_parse_create_primary(struct tpm_chip *chip, struct tpm_buf *buf,
 	u32 val, param_len, keyhandle;
 
 	keyhandle = tpm_buf_read_u32(buf, &offset_r);
-	if (handle)
-		*handle = keyhandle;
-	else
-		tpm2_flush_context(chip, keyhandle);
 
 	param_len = tpm_buf_read_u32(buf, &offset_r);
 	/*

@@ -1135,6 +1139,7 @@ static int tpm2_parse_create_primary(struct tpm_chip *chip, struct tpm_buf *buf,
 		return -EINVAL;
 	}
 
+	*handle = keyhandle;
 	return 0;
 }
 

index 854546000c92..0ea00e32f575 100644
@@ -674,6 +674,19 @@ EXPORT_SYMBOL_GPL(tpm_chip_register);
  */
 void tpm_chip_unregister(struct tpm_chip *chip)
 {
+#ifdef CONFIG_TCG_TPM2_HMAC
+	int rc;
+
+	rc = tpm_try_get_ops(chip);
+	if (!rc) {
+		if (chip->flags & TPM_CHIP_FLAG_TPM2) {
+			tpm2_flush_context(chip, chip->null_key);
+			chip->null_key = 0;
+		}
+		tpm_put_ops(chip);
+	}
+#endif
+
 	tpm_del_legacy_sysfs(chip);
 	if (tpm_is_hwrng_enabled(chip))
 		hwrng_unregister(&chip->hwrng);

index c3fbbf4d3db7..4bc07963e260 100644
@@ -27,6 +27,13 @@ static ssize_t tpm_dev_transmit(struct tpm_chip *chip, struct tpm_space *space,
 	struct tpm_header *header = (void *)buf;
 	ssize_t ret, len;
 
+#ifdef CONFIG_TCG_TPM2_HMAC
+	if (chip->flags & TPM_CHIP_FLAG_TPM2) {
+		tpm2_flush_context(chip, chip->null_key);
+		chip->null_key = 0;
+	}
+#endif
+
 	ret = tpm2_prepare_space(chip, space, buf, bufsiz);
 	/* If the command is not implemented by the TPM, synthesize a
 	 * response with a TPM2_RC_COMMAND_CODE return for user-space.

index 5da134f12c9a..bfa47d48b0f2 100644
@@ -379,10 +379,15 @@ int tpm_pm_suspend(struct device *dev)
 
 	rc = tpm_try_get_ops(chip);
 	if (!rc) {
-		if (chip->flags & TPM_CHIP_FLAG_TPM2)
+		if (chip->flags & TPM_CHIP_FLAG_TPM2) {
+#ifdef CONFIG_TCG_TPM2_HMAC
+			tpm2_flush_context(chip, chip->null_key);
+			chip->null_key = 0;
+#endif
 			tpm2_shutdown(chip, TPM2_SU_STATE);
-		else
+		} else {
 			rc = tpm1_pm_suspend(chip, tpm_suspend_pcr);
+		}
 
 		tpm_put_ops(chip);
 	}

index 1e856259219e..aba024cbe7c5 100644
@@ -364,6 +364,9 @@ void tpm2_flush_context(struct tpm_chip *chip, u32 handle)
 	struct tpm_buf buf;
 	int rc;
 
+	if (!handle)
+		return;
+
 	rc = tpm_buf_init(&buf, TPM2_ST_NO_SESSIONS, TPM2_CC_FLUSH_CONTEXT);
 	if (rc) {
 		dev_warn(&chip->dev, "0x%08x was not flushed, out of memory\n",

index 34ce0d9d4577..8d7b708ce566 100644
@@ -855,10 +855,21 @@ static int tpm2_load_null(struct tpm_chip *chip, u32 *null_key)
 	u32 tmp_null_key;
 	int rc;
 
+	/* fast path */
+	if (chip->null_key) {
+		*null_key = chip->null_key;
+		return 0;
+	}
+
 	rc = tpm2_load_context(chip, chip->null_key_context, &offset,
-			       null_key);
-	if (rc != -EINVAL)
+			       &tmp_null_key);
+	if (rc != -EINVAL) {
+		if (!rc) {
+			chip->null_key = tmp_null_key;
+			*null_key = tmp_null_key;
+		}
 		return rc;
+	}
 
 	/* an integrity failure may mean the TPM has been reset */
 	dev_err(&chip->dev, "NULL key integrity failure!\n");

@@ -869,6 +880,7 @@ static int tpm2_load_null(struct tpm_chip *chip, u32 *null_key)
 
 	/* Return the null key if the name has not been changed: */
 	if (memcmp(name, chip->null_key_name, sizeof(name)) == 0) {
+		chip->null_key = tmp_null_key;
 		*null_key = tmp_null_key;
 		return 0;
 	}

@@ -946,7 +958,6 @@ int tpm2_start_auth_session(struct tpm_chip *chip)
 	tpm_buf_append_u16(&buf, TPM_ALG_SHA256);
 
 	rc = tpm_transmit_cmd(chip, &buf, 0, "start auth session");
-	tpm2_flush_context(chip, null_key);
 
 	if (rc == TPM2_RC_SUCCESS)
 		rc = tpm2_parse_start_auth_session(auth, &buf);

@@ -1275,7 +1286,11 @@ static int tpm2_create_null_primary(struct tpm_chip *chip)
 
 		rc = tpm2_save_context(chip, null_key, chip->null_key_context,
 				       sizeof(chip->null_key_context), &offset);
-		tpm2_flush_context(chip, null_key);
+		pr_info("%s: rc=0x%08x\n", __func__, rc);
+		if (rc)
+			tpm2_flush_context(chip, null_key);
+		else
+			chip->null_key = null_key;
 	}
 
 	return rc;

index e93ee8d936a9..4eb39db80e05 100644
@@ -205,6 +205,8 @@ struct tpm_chip {
 #ifdef CONFIG_TCG_TPM2_HMAC
 	/* details for communication security via sessions */
 
+	/* loaded null key */
+	u32 null_key;
 	/* saved context for NULL seed */
 	u8 null_key_context[TPM2_MAX_CONTEXT_SIZE];
 	 /* name of NULL seed */