[PATCH] livepatch: Delete the associated module when replacing an old livepatch

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Enhance the functionality of kpatch to automatically remove the associated
module when replacing an old livepatch with a new one. This ensures that no
leftover modules remain in the system. For instance:

- Load the first livepatch
  $ kpatch load 6.9.0-rc1+/livepatch-test_0.ko
  loading patch module: 6.9.0-rc1+/livepatch-test_0.ko
  waiting (up to 15 seconds) for patch transition to complete...
  transition complete (2 seconds)

  $ kpatch list
  Loaded patch modules:
  livepatch_test_0 [enabled]

  $ lsmod |grep livepatch
  livepatch_test_0       16384  1

- Load a new livepatch
  $ kpatch load 6.9.0-rc1+/livepatch-test_1.ko
  loading patch module: 6.9.0-rc1+/livepatch-test_1.ko
  waiting (up to 15 seconds) for patch transition to complete...
  transition complete (2 seconds)

  $ kpatch list
  Loaded patch modules:
  livepatch_test_1 [enabled]

  $ lsmod |grep livepatch
  livepatch_test_1       16384  1
  livepatch_test_0       16384  0   <<<< leftover

With this improvement, executing
`kpatch load 6.9.0-rc1+/livepatch-test_1.ko` will automatically remove the
livepatch-test_0.ko module.

Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
---
 include/linux/module.h  |  1 +
 kernel/livepatch/core.c | 11 +++++++++--
 kernel/module/main.c    | 43 ++++++++++++++++++++++++-----------------
 3 files changed, 35 insertions(+), 20 deletions(-)

diff --git a/include/linux/module.h b/include/linux/module.h
index 1153b0d99a80..9a95174a919b 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -75,6 +75,7 @@ extern struct module_attribute module_uevent;
 /* These are either module local, or the kernel's dummy ones. */
 extern int init_module(void);
 extern void cleanup_module(void);
+extern void delete_module(struct module *mod);
 
 #ifndef MODULE
 /**
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index ecbc9b6aba3a..f1edc999f3ef 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -711,6 +711,8 @@ static void klp_free_patch_start(struct klp_patch *patch)
  */
 static void klp_free_patch_finish(struct klp_patch *patch)
 {
+	struct module *mod = patch->mod;
+
 	/*
 	 * Avoid deadlock with enabled_store() sysfs callback by
 	 * calling this outside klp_mutex. It is safe because
@@ -721,8 +723,13 @@ static void klp_free_patch_finish(struct klp_patch *patch)
 	wait_for_completion(&patch->finish);
 
 	/* Put the module after the last access to struct klp_patch. */
-	if (!patch->forced)
-		module_put(patch->mod);
+	if (!patch->forced)  {
+		module_put(mod);
+		if (module_refcount(mod))
+			return;
+		mod->state = MODULE_STATE_GOING;
+		delete_module(mod);
+	}
 }
 
 /*
diff --git a/kernel/module/main.c b/kernel/module/main.c
index e1e8a7a9d6c1..e863e1f87dfd 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -695,12 +695,35 @@ EXPORT_SYMBOL(module_refcount);
 /* This exists whether we can unload or not */
 static void free_module(struct module *mod);
 
+void delete_module(struct module *mod)
+{
+	char buf[MODULE_FLAGS_BUF_SIZE];
+
+	/* Final destruction now no one is using it. */
+	if (mod->exit != NULL)
+		mod->exit();
+	blocking_notifier_call_chain(&module_notify_list,
+				     MODULE_STATE_GOING, mod);
+	klp_module_going(mod);
+	ftrace_release_mod(mod);
+
+	async_synchronize_full();
+
+	/* Store the name and taints of the last unloaded module for diagnostic purposes */
+	strscpy(last_unloaded_module.name, mod->name, sizeof(last_unloaded_module.name));
+	strscpy(last_unloaded_module.taints, module_flags(mod, buf, false),
+		sizeof(last_unloaded_module.taints));
+
+	free_module(mod);
+	/* someone could wait for the module in add_unformed_module() */
+	wake_up_all(&module_wq);
+}
+
 SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
 		unsigned int, flags)
 {
 	struct module *mod;
 	char name[MODULE_NAME_LEN];
-	char buf[MODULE_FLAGS_BUF_SIZE];
 	int ret, forced = 0;
 
 	if (!capable(CAP_SYS_MODULE) || modules_disabled)
@@ -750,23 +773,7 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
 		goto out;
 
 	mutex_unlock(&module_mutex);
-	/* Final destruction now no one is using it. */
-	if (mod->exit != NULL)
-		mod->exit();
-	blocking_notifier_call_chain(&module_notify_list,
-				     MODULE_STATE_GOING, mod);
-	klp_module_going(mod);
-	ftrace_release_mod(mod);
-
-	async_synchronize_full();
-
-	/* Store the name and taints of the last unloaded module for diagnostic purposes */
-	strscpy(last_unloaded_module.name, mod->name, sizeof(last_unloaded_module.name));
-	strscpy(last_unloaded_module.taints, module_flags(mod, buf, false), sizeof(last_unloaded_module.taints));
-
-	free_module(mod);
-	/* someone could wait for the module in add_unformed_module() */
-	wake_up_all(&module_wq);
+	delete_module(mod);
 	return 0;
 out:
 	mutex_unlock(&module_mutex);
-- 
2.39.1





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