module: printk message when module signature fail taints kernel.

Reported-by: Chris Samuel <chris@csamuel.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/kernel/module.c b/kernel/module.c
index eab0827..e69a5a6 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3192,8 +3192,13 @@
 
 #ifdef CONFIG_MODULE_SIG
 	mod->sig_ok = info->sig_ok;
-	if (!mod->sig_ok)
+	if (!mod->sig_ok) {
+		printk_once(KERN_NOTICE
+			    "%s: module verification failed: signature and/or"
+			    " required key missing - tainting kernel\n",
+			    mod->name);
 		add_taint_module(mod, TAINT_FORCED_MODULE);
+	}
 #endif
 
 	/* Now module is in final location, initialize linked lists, etc. */