[PATCH v3] module: Allow to disable modsign in kernel cmdline

[Tianjia Zhang]

This option allows to disable modsign completely at the beginning,
and turn off by set the kernel cmdline `no_modsig_enforce` when
`CONFIG_MODULE_SIG_FORCE` is enabled.

Yet another change allows to always show the current status of
modsign through `/sys/module/module/parameters/sig_enforce`.

Signed-off-by: Jia Zhang <zhang.jia@xxxxxxxxxxxxxxxxx>
Signed-off-by: Tianjia Zhang <tianjia.zhang@xxxxxxxxxxxxxxxxx>
---

v3 change:
  Beautify the document description according to the recommendation.

v2 change:
  document this new option.

 Documentation/admin-guide/kernel-parameters.txt | 6 ++++++
 kernel/module.c                                 | 8 ++++++++
 2 files changed, 14 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 7bc83f3d9bdf..b30f013fb8c5 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3190,6 +3190,12 @@
 	noirqdebug	[X86-32] Disables the code which attempts to detect and
 			disable unhandled interrupt sources.
 
+	no_modsig_enforce
+			[KNL] When CONFIG_MODULE_SIG_FORCE is set, this option
+			allows to disable modsign completely at the beginning.
+			This means that modules without (valid) signatures will
+			be loaded successfully.
+
 	no_timer_check	[X86,APIC] Disables the code which tests for
 			broken timer IRQ sources.
 
diff --git a/kernel/module.c b/kernel/module.c
index 646f1e2330d2..0e68e1286377 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -269,6 +269,14 @@ static void module_assert_mutex_or_preempt(void)
 
 static bool sig_enforce = IS_ENABLED(CONFIG_MODULE_SIG_FORCE);
 module_param(sig_enforce, bool_enable_only, 0644);
+#ifdef CONFIG_MODULE_SIG_FORCE
+static int __init set_no_modsig_enforce(char *str)
+{
+	sig_enforce = false;
+	return 1;
+}
+__setup("no_modsig_enforce", set_no_modsig_enforce);
+#endif /* !CONFIG_MODULE_SIG_FORCE */
 
 /*
  * Export sig_enforce kernel cmdline parameter to allow other subsystems rely
-- 
2.17.1