powerpc/secvar: Allow backend to populate static list of variable names

Currently, the list of variables is populated by calling
secvar_ops->get_next() repeatedly, which is explicitly modelled on the
OPAL API (including the keylen parameter).

For the upcoming PLPKS backend, we have a static list of variable names.
It is messy to fit that into get_next(), so instead, let the backend put
a NULL-terminated array of variable names into secvar_ops->var_names,
which will be used if get_next() is undefined.
Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Russell Currey <ruscur@russell.cc>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230210080401.345462-12-ajd@linux.ibm.com

arch/powerpc/include/asm/secvar.h

@@ -21,6 +21,10 @@ struct secvar_operations {
 	ssize_t (*format)(char *buf, size_t bufsize);
 	int (*max_size)(u64 *max_size);
 	const struct attribute **config_attrs;
+
+	// NULL-terminated array of fixed variable names
+	// Only used if get_next() isn't provided
+	const char * const *var_names;
 };
 
 #ifdef CONFIG_PPC_SECURE_BOOT

arch/powerpc/kernel/secvar-sysfs.c

@@ -157,9 +157,31 @@ static int secvar_sysfs_config(struct kobject *kobj)
 	return 0;
 }
 
-static int secvar_sysfs_load(void)
+static int add_var(const char *name)
 {
 	struct kobject *kobj;
+	int rc;
+
+	kobj = kzalloc(sizeof(*kobj), GFP_KERNEL);
+	if (!kobj)
+		return -ENOMEM;
+
+	kobject_init(kobj, &secvar_ktype);
+
+	rc = kobject_add(kobj, &secvar_kset->kobj, "%s", name);
+	if (rc) {
+		pr_warn("kobject_add error %d for attribute: %s\n", rc,
+			name);
+		kobject_put(kobj);
+		return rc;
+	}
+
+	kobject_uevent(kobj, KOBJ_ADD);
+	return 0;
+}
+
+static int secvar_sysfs_load(void)
+{
 	u64 namesize = 0;
 	char *name;
 	int rc;
@@ -179,31 +201,28 @@ static int secvar_sysfs_load(void)
 			break;
 		}
 
-		kobj = kzalloc(sizeof(*kobj), GFP_KERNEL);
-		if (!kobj) {
-			rc = -ENOMEM;
-			break;
-		}
-
-		kobject_init(kobj, &secvar_ktype);
-
-		rc = kobject_add(kobj, &secvar_kset->kobj, "%s", name);
-		if (rc) {
-			pr_warn("kobject_add error %d for attribute: %s\n", rc,
-				name);
-			kobject_put(kobj);
-			kobj = NULL;
-		}
-
-		if (kobj)
-			kobject_uevent(kobj, KOBJ_ADD);
-
+		rc = add_var(name);
 	} while (!rc);
 
 	kfree(name);
 	return rc;
 }
 
+static int secvar_sysfs_load_static(void)
+{
+	const char * const *name_ptr = secvar_ops->var_names;
+	int rc;
+
+	while (*name_ptr) {
+		rc = add_var(*name_ptr);
+		if (rc)
+			return rc;
+		name_ptr++;
+	}
+
+	return 0;
+}
+
 static int secvar_sysfs_init(void)
 {
 	int rc;
@@ -245,7 +264,15 @@ static int secvar_sysfs_init(void)
 		goto err;
 	}
 
-	secvar_sysfs_load();
+	if (secvar_ops->get_next)
+		rc = secvar_sysfs_load();
+	else
+		rc = secvar_sysfs_load_static();
+
+	if (rc) {
+		pr_err("Failed to create variable attributes\n");
+		goto err;
+	}
 
 	return 0;
 err: