diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index f32d0ee91e70e..36941d7fd6ad1 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -545,8 +545,8 @@ struct key *
 fscrypt_find_master_key(struct super_block *sb,
 			const struct fscrypt_key_specifier *mk_spec);
 
-int fscrypt_add_test_dummy_key(struct super_block *sb,
-			       struct fscrypt_key_specifier *key_spec);
+int fscrypt_get_test_dummy_key_identifier(
+			  u8 key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]);
 
 int fscrypt_verify_key_added(struct super_block *sb,
 			     const u8 identifier[FSCRYPT_KEY_IDENTIFIER_SIZE]);
diff --git a/fs/crypto/keyring.c b/fs/crypto/keyring.c
index 0b3ffbb4faf4a..caee9f8620dd9 100644
--- a/fs/crypto/keyring.c
+++ b/fs/crypto/keyring.c
@@ -688,28 +688,68 @@ int fscrypt_ioctl_add_key(struct file *filp, void __user *_uarg)
 }
 EXPORT_SYMBOL_GPL(fscrypt_ioctl_add_key);
 
-/*
- * Add the key for '-o test_dummy_encryption' to the filesystem keyring.
- *
- * Use a per-boot random key to prevent people from misusing this option.
- */
-int fscrypt_add_test_dummy_key(struct super_block *sb,
-			       struct fscrypt_key_specifier *key_spec)
+static void
+fscrypt_get_test_dummy_secret(struct fscrypt_master_key_secret *secret)
 {
 	static u8 test_key[FSCRYPT_MAX_KEY_SIZE];
+
+	get_random_once(test_key, FSCRYPT_MAX_KEY_SIZE);
+
+	memset(secret, 0, sizeof(*secret));
+	secret->size = FSCRYPT_MAX_KEY_SIZE;
+	memcpy(secret->raw, test_key, FSCRYPT_MAX_KEY_SIZE);
+}
+
+int fscrypt_get_test_dummy_key_identifier(
+				u8 key_identifier[FSCRYPT_KEY_IDENTIFIER_SIZE])
+{
 	struct fscrypt_master_key_secret secret;
 	int err;
 
-	get_random_once(test_key, FSCRYPT_MAX_KEY_SIZE);
+	fscrypt_get_test_dummy_secret(&secret);
 
-	memset(&secret, 0, sizeof(secret));
-	secret.size = FSCRYPT_MAX_KEY_SIZE;
-	memcpy(secret.raw, test_key, FSCRYPT_MAX_KEY_SIZE);
+	err = fscrypt_init_hkdf(&secret.hkdf, secret.raw, secret.size);
+	if (err)
+		goto out;
+	err = fscrypt_hkdf_expand(&secret.hkdf, HKDF_CONTEXT_KEY_IDENTIFIER,
+				  NULL, 0, key_identifier,
+				  FSCRYPT_KEY_IDENTIFIER_SIZE);
+out:
+	wipe_master_key_secret(&secret);
+	return err;
+}
+
+/**
+ * fscrypt_add_test_dummy_key() - add the test dummy encryption key
+ * @sb: the filesystem instance to add the key to
+ * @dummy_policy: the encryption policy for test_dummy_encryption
+ *
+ * If needed, add the key for the test_dummy_encryption mount option to the
+ * filesystem.  To prevent misuse of this mount option, a per-boot random key is
+ * used instead of a hardcoded one.  This makes it so that any encrypted files
+ * created using this option won't be accessible after a reboot.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fscrypt_add_test_dummy_key(struct super_block *sb,
+			       const struct fscrypt_dummy_policy *dummy_policy)
+{
+	const union fscrypt_policy *policy = dummy_policy->policy;
+	struct fscrypt_key_specifier key_spec;
+	struct fscrypt_master_key_secret secret;
+	int err;
 
-	err = add_master_key(sb, &secret, key_spec);
+	if (!policy)
+		return 0;
+	err = fscrypt_policy_to_key_spec(policy, &key_spec);
+	if (err)
+		return err;
+	fscrypt_get_test_dummy_secret(&secret);
+	err = add_master_key(sb, &secret, &key_spec);
 	wipe_master_key_secret(&secret);
 	return err;
 }
+EXPORT_SYMBOL_GPL(fscrypt_add_test_dummy_key);
 
 /*
  * Verify that the current user has added a master key with the given identifier
diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index 2a11276913a98..5f858cee1e3b0 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -10,6 +10,7 @@
  * Modified by Eric Biggers, 2019 for v2 policy support.
  */
 
+#include <linux/fs_context.h>
 #include <linux/random.h>
 #include <linux/seq_file.h>
 #include <linux/string.h>
@@ -724,73 +725,45 @@ int fscrypt_set_context(struct inode *inode, void *fs_data)
 EXPORT_SYMBOL_GPL(fscrypt_set_context);
 
 /**
- * fscrypt_set_test_dummy_encryption() - handle '-o test_dummy_encryption'
- * @sb: the filesystem on which test_dummy_encryption is being specified
- * @arg: the argument to the test_dummy_encryption option.  May be NULL.
- * @dummy_policy: the filesystem's current dummy policy (input/output, see
- *		  below)
+ * fscrypt_parse_test_dummy_encryption() - parse the test_dummy_encryption mount option
+ * @param: the mount option
+ * @dummy_policy: (input/output) the place to write the dummy policy that will
+ *	result from parsing the option.  Zero-initialize this.  If a policy is
+ *	already set here (due to test_dummy_encryption being given multiple
+ *	times), then this function will verify that the policies are the same.
  *
- * Handle the test_dummy_encryption mount option by creating a dummy encryption
- * policy, saving it in @dummy_policy, and adding the corresponding dummy
- * encryption key to the filesystem.  If the @dummy_policy is already set, then
- * instead validate that it matches @arg.  Don't support changing it via
- * remount, as that is difficult to do safely.
- *
- * Return: 0 on success (dummy policy set, or the same policy is already set);
- *         -EEXIST if a different dummy policy is already set;
- *         or another -errno value.
+ * Return: 0 on success; -EINVAL if the argument is invalid; -EEXIST if the
+ *	   argument conflicts with one already specified; or -ENOMEM.
  */
-int fscrypt_set_test_dummy_encryption(struct super_block *sb, const char *arg,
-				      struct fscrypt_dummy_policy *dummy_policy)
+int fscrypt_parse_test_dummy_encryption(const struct fs_parameter *param,
+				struct fscrypt_dummy_policy *dummy_policy)
 {
-	struct fscrypt_key_specifier key_spec = { 0 };
-	int version;
-	union fscrypt_policy *policy = NULL;
+	const char *arg = "v2";
+	union fscrypt_policy *policy;
 	int err;
 
-	if (!arg)
-		arg = "v2";
-
-	if (!strcmp(arg, "v1")) {
-		version = FSCRYPT_POLICY_V1;
-		key_spec.type = FSCRYPT_KEY_SPEC_TYPE_DESCRIPTOR;
-		memset(key_spec.u.descriptor, 0x42,
-		       FSCRYPT_KEY_DESCRIPTOR_SIZE);
-	} else if (!strcmp(arg, "v2")) {
-		version = FSCRYPT_POLICY_V2;
-		key_spec.type = FSCRYPT_KEY_SPEC_TYPE_IDENTIFIER;
-		/* key_spec.u.identifier gets filled in when adding the key */
-	} else {
-		err = -EINVAL;
-		goto out;
-	}
+	if (param->type == fs_value_is_string && *param->string)
+		arg = param->string;
 
 	policy = kzalloc(sizeof(*policy), GFP_KERNEL);
-	if (!policy) {
-		err = -ENOMEM;
-		goto out;
-	}
-
-	err = fscrypt_add_test_dummy_key(sb, &key_spec);
-	if (err)
-		goto out;
+	if (!policy)
+		return -ENOMEM;
 
-	policy->version = version;
-	switch (policy->version) {
-	case FSCRYPT_POLICY_V1:
+	if (!strcmp(arg, "v1")) {
+		policy->version = FSCRYPT_POLICY_V1;
 		policy->v1.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
 		policy->v1.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
-		memcpy(policy->v1.master_key_descriptor, key_spec.u.descriptor,
+		memset(policy->v1.master_key_descriptor, 0x42,
 		       FSCRYPT_KEY_DESCRIPTOR_SIZE);
-		break;
-	case FSCRYPT_POLICY_V2:
+	} else if (!strcmp(arg, "v2")) {
+		policy->version = FSCRYPT_POLICY_V2;
 		policy->v2.contents_encryption_mode = FSCRYPT_MODE_AES_256_XTS;
 		policy->v2.filenames_encryption_mode = FSCRYPT_MODE_AES_256_CTS;
-		memcpy(policy->v2.master_key_identifier, key_spec.u.identifier,
-		       FSCRYPT_KEY_IDENTIFIER_SIZE);
-		break;
-	default:
-		WARN_ON(1);
+		err = fscrypt_get_test_dummy_key_identifier(
+				policy->v2.master_key_identifier);
+		if (err)
+			goto out;
+	} else {
 		err = -EINVAL;
 		goto out;
 	}
@@ -809,6 +782,37 @@ int fscrypt_set_test_dummy_encryption(struct super_block *sb, const char *arg,
 	kfree(policy);
 	return err;
 }
+EXPORT_SYMBOL_GPL(fscrypt_parse_test_dummy_encryption);
+
+/**
+ * fscrypt_dummy_policies_equal() - check whether two dummy policies are equal
+ * @p1: the first test dummy policy (may be unset)
+ * @p2: the second test dummy policy (may be unset)
+ *
+ * Return: %true if the dummy policies are both set and equal, or both unset.
+ */
+bool fscrypt_dummy_policies_equal(const struct fscrypt_dummy_policy *p1,
+				  const struct fscrypt_dummy_policy *p2)
+{
+	if (!p1->policy && !p2->policy)
+		return true;
+	if (!p1->policy || !p2->policy)
+		return false;
+	return fscrypt_policies_equal(p1->policy, p2->policy);
+}
+EXPORT_SYMBOL_GPL(fscrypt_dummy_policies_equal);
+
+/* Deprecated, do not use */
+int fscrypt_set_test_dummy_encryption(struct super_block *sb, const char *arg,
+				      struct fscrypt_dummy_policy *dummy_policy)
+{
+	struct fs_parameter param = {
+		.type = fs_value_is_string,
+		.string = arg ? (char *)arg : "",
+	};
+	return fscrypt_parse_test_dummy_encryption(&param, dummy_policy) ?:
+		fscrypt_add_test_dummy_key(sb, dummy_policy);
+}
 EXPORT_SYMBOL_GPL(fscrypt_set_test_dummy_encryption);
 
 /**
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index 50d92d805bd8c..099b881e63e49 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -22,6 +22,7 @@
 
 union fscrypt_policy;
 struct fscrypt_info;
+struct fs_parameter;
 struct seq_file;
 
 struct fscrypt_str {
@@ -279,10 +280,19 @@ struct fscrypt_dummy_policy {
 	const union fscrypt_policy *policy;
 };
 
+int fscrypt_parse_test_dummy_encryption(const struct fs_parameter *param,
+				    struct fscrypt_dummy_policy *dummy_policy);
+bool fscrypt_dummy_policies_equal(const struct fscrypt_dummy_policy *p1,
+				  const struct fscrypt_dummy_policy *p2);
 int fscrypt_set_test_dummy_encryption(struct super_block *sb, const char *arg,
 				struct fscrypt_dummy_policy *dummy_policy);
 void fscrypt_show_test_dummy_encryption(struct seq_file *seq, char sep,
 					struct super_block *sb);
+static inline bool
+fscrypt_is_dummy_policy_set(const struct fscrypt_dummy_policy *dummy_policy)
+{
+	return dummy_policy->policy != NULL;
+}
 static inline void
 fscrypt_free_dummy_policy(struct fscrypt_dummy_policy *dummy_policy)
 {
@@ -293,6 +303,8 @@ fscrypt_free_dummy_policy(struct fscrypt_dummy_policy *dummy_policy)
 /* keyring.c */
 void fscrypt_sb_free(struct super_block *sb);
 int fscrypt_ioctl_add_key(struct file *filp, void __user *arg);
+int fscrypt_add_test_dummy_key(struct super_block *sb,
+			       const struct fscrypt_dummy_policy *dummy_policy);
 int fscrypt_ioctl_remove_key(struct file *filp, void __user *arg);
 int fscrypt_ioctl_remove_key_all_users(struct file *filp, void __user *arg);
 int fscrypt_ioctl_get_key_status(struct file *filp, void __user *arg);
@@ -467,12 +479,32 @@ static inline int fscrypt_set_context(struct inode *inode, void *fs_data)
 struct fscrypt_dummy_policy {
 };
 
+static inline int
+fscrypt_parse_test_dummy_encryption(const struct fs_parameter *param,
+				    struct fscrypt_dummy_policy *dummy_policy)
+{
+	return -EINVAL;
+}
+
+static inline bool
+fscrypt_dummy_policies_equal(const struct fscrypt_dummy_policy *p1,
+			     const struct fscrypt_dummy_policy *p2)
+{
+	return true;
+}
+
 static inline void fscrypt_show_test_dummy_encryption(struct seq_file *seq,
 						      char sep,
 						      struct super_block *sb)
 {
 }
 
+static inline bool
+fscrypt_is_dummy_policy_set(const struct fscrypt_dummy_policy *dummy_policy)
+{
+	return false;
+}
+
 static inline void
 fscrypt_free_dummy_policy(struct fscrypt_dummy_policy *dummy_policy)
 {
@@ -488,6 +520,13 @@ static inline int fscrypt_ioctl_add_key(struct file *filp, void __user *arg)
 	return -EOPNOTSUPP;
 }
 
+static inline int
+fscrypt_add_test_dummy_key(struct super_block *sb,
+			   const struct fscrypt_dummy_policy *dummy_policy)
+{
+	return 0;
+}
+
 static inline int fscrypt_ioctl_remove_key(struct file *filp, void __user *arg)
 {
 	return -EOPNOTSUPP;
