kernel/module.c: avoid ifdefs for sig_enforce declaration

There's no need to require an ifdef over the declaration
of sig_enforce as IS_ENABLED() can be used. While at it,
there's no harm in exposing this kernel parameter outside of
CONFIG_MODULE_SIG as it'd be a no-op on non module sig
kernels.

Now, technically we should in theory be able to remove
the #ifdef'ery over the declaration of the module parameter
as we are also trusting the bool_enable_only code for
CONFIG_MODULE_SIG kernels but for now remain paranoid
and keep it.

With time if no one can put a bullet through bool_enable_only
and if there are no technical requirements over not exposing
CONFIG_MODULE_SIG_FORCE with the measures in place by
bool_enable_only we could remove this last ifdef.

Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: linux-kernel@vger.kernel.org
Cc: cocci@systeme.lip6.fr
Signed-off-by: Luis R. Rodriguez <mcgrof@suse.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

kernel/module.c

@@ -292,15 +292,10 @@ static void module_assert_mutex_or_preempt(void)
 #endif
 }
 
-#ifdef CONFIG_MODULE_SIG
-#ifdef CONFIG_MODULE_SIG_FORCE
-static bool sig_enforce = true;
-#else
-static bool sig_enforce = false;
-
+static bool sig_enforce = IS_ENABLED(CONFIG_MODULE_SIG_FORCE);
+#ifndef CONFIG_MODULE_SIG_FORCE
 module_param(sig_enforce, bool_enable_only, 0644);
 #endif /* !CONFIG_MODULE_SIG_FORCE */
-#endif /* CONFIG_MODULE_SIG */
 
 /* Block module loading/unloading? */
 int modules_disabled = 0;