linux-kernel - [PATCH v4] module: Add CONFIG_MODULE_DISABLE_INIT

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Date:   Thu, 12 Oct 2023 07:17:19 +0530
From:   Joey Jiao <quic_jiangenj@...cinc.com>
To:     <linux-modules@...r.kernel.org>
CC:     <quic_jiangenj@...cinc.com>, Luis Chamberlain <mcgrof@...nel.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH v4] module: Add CONFIG_MODULE_DISABLE_INIT_FREE option

To facilitate syzkaller test, it's essential for the module to retain the
same address across reboots. In userspace, the execution of modprobe
commands must occur sequentially. In the kernel, selecting the
CONFIG_MODULE_DISABLE_INIT_FREE option disables the asynchronous freeing
of init sections.

Signed-off-by: Joey Jiao <quic_jiangenj@...cinc.com>
---
 kernel/module/Kconfig | 12 ++++++++++++
 kernel/module/main.c  |  3 ++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
index 33a2e991f608..88206bc4c7d4 100644
--- a/kernel/module/Kconfig
+++ b/kernel/module/Kconfig
@@ -389,4 +389,16 @@ config MODULES_TREE_LOOKUP
 	def_bool y
 	depends on PERF_EVENTS || TRACING || CFI_CLANG
 
+config MODULE_DISABLE_INIT_FREE
+	bool "Disable freeing of init sections"
+	default n
+	help
+	  By default, kernel will free init sections after module being fully
+	  loaded.
+
+	  MODULE_DISABLE_INIT_FREE allows users to prevent the freeing of init
+	  sections. This option is particularly helpful for syzkaller fuzzing,
+	  ensuring that the module consistently loads into the same address
+	  across reboots.
+
 endif # MODULES
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 98fedfdb8db5..0f242b7b29fe 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2593,7 +2593,8 @@ static noinline int do_init_module(struct module *mod)
 	 * be cleaned up needs to sync with the queued work - ie
 	 * rcu_barrier()
 	 */
-	if (llist_add(&freeinit->node, &init_free_list))
+	if (llist_add(&freeinit->node, &init_free_list) &&
+		!IS_ENABLED(CONFIG_MODULE_DISABLE_INIT_FREE))
 		schedule_work(&init_free_wq);
 
 	mutex_unlock(&module_mutex);
-- 
2.42.0