module: limit enabling module.sig_enforce

Irrespective as to whether CONFIG_MODULE_SIG is configured, specifying
"module.sig_enforce=1" on the boot command line sets "sig_enforce".
Only allow "sig_enforce" to be set when CONFIG_MODULE_SIG is configured.

This patch makes the presence of /sys/module/module/parameters/sig_enforce
dependent on CONFIG_MODULE_SIG=y.

Fixes: fda784e5 ("module: export module signature enforcement status")
Reported-by: Nayna Jain <nayna@linux.ibm.com>
Tested-by: Mimi Zohar <zohar@linux.ibm.com>
Tested-by: Jessica Yu <jeyu@kernel.org>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Jessica Yu <jeyu@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/module.c

@@ -266,9 +266,18 @@ static void module_assert_mutex_or_preempt(void)
 #endif
 }
 
+#ifdef CONFIG_MODULE_SIG
 static bool sig_enforce = IS_ENABLED(CONFIG_MODULE_SIG_FORCE);
 module_param(sig_enforce, bool_enable_only, 0644);
 
+void set_module_sig_enforced(void)
+{
+	sig_enforce = true;
+}
+#else
+#define sig_enforce false
+#endif
+
 /*
  * Export sig_enforce kernel cmdline parameter to allow other subsystems rely
  * on that instead of directly to CONFIG_MODULE_SIG_FORCE config.
@@ -279,11 +288,6 @@ bool is_module_sig_enforced(void)
 }
 EXPORT_SYMBOL(is_module_sig_enforced);
 
-void set_module_sig_enforced(void)
-{
-	sig_enforce = true;
-}
-
 /* Block module loading/unloading? */
 int modules_disabled = 0;
 core_param(nomodule, modules_disabled, bint, 0);