module: Add module specific symbol namespace support

Designate the "module:${modname}" symbol namespace to mean: 'only
export to the named module'.

Notably, explicit imports of anything in the "module:" space is
forbidden.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Author: Peter Zijlstra

kernel/module/main.c

@@ -1083,6 +1083,14 @@ static char *get_modinfo(const struct load_info *info, const char *tag)
 	return get_next_modinfo(info, tag, NULL);
 }
 
+static bool verify_module_namespace(const char *namespace, const char *modname)
+{
+	const char *prefix = "module:";
+
+	return strstarts(namespace, prefix) &&
+	       !strcmp(namespace + strlen(prefix), modname);
+}
+
 static int verify_namespace_is_imported(const struct load_info *info,
 					const struct kernel_symbol *sym,
 					struct module *mod)
@@ -1092,6 +1100,10 @@ static int verify_namespace_is_imported(const struct load_info *info,
 
 	namespace = kernel_symbol_namespace(sym);
 	if (namespace && namespace[0]) {
+
+		if (verify_module_namespace(namespace, mod->name))
+			return 0;
+
 		for_each_modinfo_entry(imported_namespace, info, "import_ns") {
 			if (strcmp(namespace, imported_namespace) == 0)
 				return 0;
@@ -1659,15 +1671,30 @@ static void module_license_taint_check(struct module *mod, const char *license)
 	}
 }
 
-static void setup_modinfo(struct module *mod, struct load_info *info)
+static int setup_modinfo(struct module *mod, struct load_info *info)
 {
 	const struct module_attribute *attr;
+	char *imported_namespace;
 	int i;
 
 	for (i = 0; (attr = modinfo_attrs[i]); i++) {
 		if (attr->setup)
 			attr->setup(mod, get_modinfo(info, attr->attr.name));
 	}
+
+	for_each_modinfo_entry(imported_namespace, info, "import_ns") {
+		/*
+		 * 'module:' prefixed namespaces are implicit, disallow
+		 * explicit imports.
+		 */
+		if (strstarts(imported_namespace, "module:")) {
+			pr_err("%s: module tries to import module namespace: %s\n",
+			       mod->name, imported_namespace);
+			return -EPERM;
+		}
+	}
+
+	return 0;
 }
 
 static void free_modinfo(struct module *mod)
@@ -3335,7 +3362,9 @@ static int load_module(struct load_info *info, const char __user *uargs,
 		goto free_unload;
 
 	/* Set up MODINFO_ATTR fields */
-	setup_modinfo(mod, info);
+	err = setup_modinfo(mod, info);
+	if (err)
+		goto free_modinfo;
 
 	/* Fix up syms, so that st_value is a pointer to location. */
 	err = simplify_symbols(mod, info);

scripts/mod/modpost.c

@@ -1682,6 +1682,14 @@ void buf_write(struct buffer *buf, const char *s, int len)
 	buf->pos += len;
 }
 
+static bool verify_module_namespace(const char *namespace, const char *modname)
+{
+	const char *prefix = "module:";
+
+	return strstarts(namespace, prefix) &&
+	       !strcmp(namespace + strlen(prefix), modname);
+}
+
 static void check_exports(struct module *mod)
 {
 	struct symbol *s, *exp;
@@ -1709,7 +1717,8 @@ static void check_exports(struct module *mod)
 
 		basename = get_basename(mod->name);
 
-		if (!contains_namespace(&mod->imported_namespaces, exp->namespace)) {
+		if (!verify_module_namespace(exp->namespace, basename) &&
+		    !contains_namespace(&mod->imported_namespaces, exp->namespace)) {
 			modpost_log(!allow_missing_ns_imports,
 				    "module %s uses symbol %s from namespace %s, but does not import it.\n",
 				    basename, exp->name, exp->namespace);