[RFC][PATCH 6/8] module: Add module specific symbol namespace support

[Peter Zijlstra]

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. Modules implicitly get the "MODULE_${modname}" namespace
added.

Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
 kernel/module/main.c  |   28 ++++++++++++++++++++++++++--
 scripts/mod/modpost.c |    5 +++++
 2 files changed, 31 insertions(+), 2 deletions(-)

--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1070,6 +1070,13 @@ static int verify_namespace_is_imported(
 
        namespace = kernel_symbol_namespace(sym);
        if (namespace && namespace[0]) {
+               /*
+                * Implicitly import MODULE_${mod->name} namespace.
+                */
+               if (strncmp(namespace, "MODULE_", 7) == 0 &&
+                   strcmp(namespace+7, mod->name) == 0)
+                       return 0;
+
                for_each_modinfo_entry(imported_namespace, info, "import_ns") {
                        if (strcmp(namespace, imported_namespace) == 0)
                                return 0;
@@ -1613,15 +1620,30 @@ static void module_license_taint_check(s
        }
 }
 
-static void setup_modinfo(struct module *mod, struct load_info *info)
+static int setup_modinfo(struct module *mod, struct load_info *info)
 {
        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)
@@ -2935,7 +2957,9 @@ static int load_module(struct load_info
                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);
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1565,6 +1565,7 @@ static const char *mod_basename(const ch
 
 static void read_symbols(const char *modname)
 {
+       char module_namespace[MODULE_NAME_LEN + 8];
        const char *symname;
        char *version;
        char *license;
@@ -1600,6 +1601,10 @@ static void read_symbols(const char *mod
                     namespace = get_next_modinfo(&info, "import_ns", 
namespace))
                        add_namespace(&mod->imported_namespaces, namespace);
 
+               snprintf(module_namespace, sizeof(module_namespace), 
"MODULE_%s",
+                        mod_basename(mod->name));
+               add_namespace(&mod->imported_namespaces, module_namespace);
+
                if (extra_warn && !get_modinfo(&info, "description"))
                        warn("missing MODULE_DESCRIPTION() in %s\n", modname);
        }