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From:   Joey Jiao <quic_jiangenj@quicinc.com>
To:     <linux-modules@vger.kernel.org>
CC:     <quic_jiangenj@quicinc.com>, Luis Chamberlain <mcgrof@kernel.org>,
        <linux-kernel@vger.kernel.org>
Subject: [PATCH v3] module: Add CONFIG_MODULE_DISABLE_INIT_FREE option
Date:   Thu, 12 Oct 2023 07:10:11 +0530
Message-ID: <20231012014012.9030-1-quic_jiangenj@quicinc.com>
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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@quicinc.com>
---
 kernel/module/Kconfig | 8 ++++++++
 kernel/module/main.c  | 5 +++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
index 33a2e991f608..1cdbee4c51de 100644
--- a/kernel/module/Kconfig
+++ b/kernel/module/Kconfig
@@ -389,4 +389,12 @@ 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
+	  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..a5210b90c078 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -2593,8 +2593,9 @@ 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))
-		schedule_work(&init_free_wq);
+	if (llist_add(&freeinit->node, &init_free_list) &&
+		!IS_ENABLED(CONFIG_MODULE_DISABLE_INIT_FREE))
+			schedule_work(&init_free_wq);
 
 	mutex_unlock(&module_mutex);
 	wake_up_all(&module_wq);
-- 
2.42.0