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Subject[PATCH v4 4/4] livepatch/module: remove livepatch module notifier
Date
Remove the livepatch module notifier in favor of directly enabling and
disabling patches to modules in the module loader. Hard-coding the
function calls ensures that ftrace_module_enable() is run before
klp_module_coming() during module load, and that klp_module_going() is
run before ftrace_release_mod() during module unload. This way, ftrace
and livepatch code is run in the correct order during the module
load/unload sequence without dependence on the module notifier call chain.

This fixes a notifier ordering issue in which the ftrace module notifier
(and hence ftrace_module_enable()) for coming modules was being called
after klp_module_notify(), which caused livepatch modules to initialize
incorrectly.

Signed-off-by: Jessica Yu <jeyu@redhat.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
---
include/linux/livepatch.h | 9 +++
kernel/livepatch/core.c | 145 ++++++++++++++++++++++------------------------
kernel/module.c | 9 +++
3 files changed, 87 insertions(+), 76 deletions(-)

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index a882865..bd830d5 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -134,6 +134,15 @@ int klp_unregister_patch(struct klp_patch *);
int klp_enable_patch(struct klp_patch *);
int klp_disable_patch(struct klp_patch *);

+/* Called from the module loader during module coming/going states */
+int klp_module_coming(struct module *mod);
+void klp_module_going(struct module *mod);
+
+#else /* !CONFIG_LIVEPATCH */
+
+static inline int klp_module_coming(struct module *mod) { return 0; }
+static inline void klp_module_going(struct module *mod) { }
+
#endif /* CONFIG_LIVEPATCH */

#endif /* _LINUX_LIVEPATCH_H_ */
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index bc2c85c..e902377 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -99,12 +99,12 @@ static void klp_find_object_module(struct klp_object *obj)
/*
* We do not want to block removal of patched modules and therefore
* we do not take a reference here. The patches are removed by
- * a going module handler instead.
+ * klp_module_going() instead.
*/
mod = find_module(obj->name);
/*
- * Do not mess work of the module coming and going notifiers.
- * Note that the patch might still be needed before the going handler
+ * Do not mess work of klp_module_coming() and klp_module_going().
+ * Note that the patch might still be needed before klp_module_going()
* is called. Module functions can be called even in the GOING state
* until mod->exit() finishes. This is especially important for
* patches that modify semantic of the functions.
@@ -866,103 +866,106 @@ int klp_register_patch(struct klp_patch *patch)
}
EXPORT_SYMBOL_GPL(klp_register_patch);

-static int klp_module_notify_coming(struct klp_patch *patch,
- struct klp_object *obj)
+int klp_module_coming(struct module *mod)
{
- struct module *pmod = patch->mod;
- struct module *mod = obj->mod;
int ret;
+ struct klp_patch *patch;
+ struct klp_object *obj;

- ret = klp_init_object_loaded(patch, obj);
- if (ret) {
- pr_warn("failed to initialize patch '%s' for module '%s' (%d)\n",
- pmod->name, mod->name, ret);
- return ret;
- }
+ if (WARN_ON(mod->state != MODULE_STATE_COMING))
+ return -EINVAL;

- if (patch->state == KLP_DISABLED)
- return 0;
+ mutex_lock(&klp_mutex);
+ /*
+ * Each module has to know that klp_module_coming()
+ * has been called. We never know what module will
+ * get patched by a new patch.
+ */
+ mod->klp_alive = true;

- pr_notice("applying patch '%s' to loading module '%s'\n",
- pmod->name, mod->name);
+ list_for_each_entry(patch, &klp_patches, list) {
+ klp_for_each_object(patch, obj) {
+ if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
+ continue;

- ret = klp_enable_object(obj);
- if (ret)
- pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
- pmod->name, mod->name, ret);
- return ret;
-}
+ obj->mod = mod;

-static void klp_module_notify_going(struct klp_patch *patch,
- struct klp_object *obj)
-{
- struct module *pmod = patch->mod;
- struct module *mod = obj->mod;
+ ret = klp_init_object_loaded(patch, obj);
+ if (ret) {
+ pr_warn("failed to initialize patch '%s' for module '%s' (%d)\n",
+ patch->mod->name, obj->mod->name, ret);
+ goto err;
+ }

- if (patch->state == KLP_DISABLED)
- goto disabled;
+ if (patch->state == KLP_DISABLED)
+ break;
+
+ pr_notice("applying patch '%s' to loading module '%s'\n",
+ patch->mod->name, obj->mod->name);
+
+ ret = klp_enable_object(obj);
+ if (ret) {
+ pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
+ patch->mod->name, obj->mod->name, ret);
+ goto err;
+ }
+
+ break;
+ }
+ }

- pr_notice("reverting patch '%s' on unloading module '%s'\n",
- pmod->name, mod->name);
+ mutex_unlock(&klp_mutex);

- klp_disable_object(obj);
+ return 0;

-disabled:
+err:
+ /*
+ * If a patch is unsuccessfully applied, return
+ * error to the module loader.
+ */
+ pr_warn("patch '%s' failed for module '%s', refusing to load module '%s'\n",
+ patch->mod->name, obj->mod->name, obj->mod->name);
klp_free_object_loaded(obj);
+ mutex_unlock(&klp_mutex);
+
+ return ret;
}

-static int klp_module_notify(struct notifier_block *nb, unsigned long action,
- void *data)
+void klp_module_going(struct module *mod)
{
- int ret;
- struct module *mod = data;
struct klp_patch *patch;
struct klp_object *obj;

- if (action != MODULE_STATE_COMING && action != MODULE_STATE_GOING)
- return 0;
+ if (WARN_ON(mod->state != MODULE_STATE_GOING))
+ return;

mutex_lock(&klp_mutex);
-
/*
- * Each module has to know that the notifier has been called.
- * We never know what module will get patched by a new patch.
+ * Each module has to know that klp_module_going()
+ * has been called. We never know what module will
+ * get patched by a new patch.
*/
- if (action == MODULE_STATE_COMING)
- mod->klp_alive = true;
- else /* MODULE_STATE_GOING */
- mod->klp_alive = false;
+ mod->klp_alive = false;

list_for_each_entry(patch, &klp_patches, list) {
klp_for_each_object(patch, obj) {
if (!klp_is_module(obj) || strcmp(obj->name, mod->name))
continue;

- if (action == MODULE_STATE_COMING) {
- obj->mod = mod;
- ret = klp_module_notify_coming(patch, obj);
- if (ret) {
- obj->mod = NULL;
- pr_warn("patch '%s' is in an inconsistent state!\n",
- patch->mod->name);
- }
- } else /* MODULE_STATE_GOING */
- klp_module_notify_going(patch, obj);
+ if (patch->state != KLP_DISABLED) {
+ pr_notice("reverting patch '%s' on unloading module '%s'\n",
+ patch->mod->name, obj->mod->name);
+ klp_disable_object(obj);
+ }

+ klp_free_object_loaded(obj);
break;
}
}

mutex_unlock(&klp_mutex);
-
- return 0;
}

-static struct notifier_block klp_module_nb = {
- .notifier_call = klp_module_notify,
- .priority = INT_MIN+1, /* called late but before ftrace notifier */
-};
-
static int __init klp_init(void)
{
int ret;
@@ -973,21 +976,11 @@ static int __init klp_init(void)
return -EINVAL;
}

- ret = register_module_notifier(&klp_module_nb);
- if (ret)
- return ret;
-
klp_root_kobj = kobject_create_and_add("livepatch", kernel_kobj);
- if (!klp_root_kobj) {
- ret = -ENOMEM;
- goto unregister;
- }
+ if (!klp_root_kobj)
+ return -ENOMEM;

return 0;
-
-unregister:
- unregister_module_notifier(&klp_module_nb);
- return ret;
}

module_init(klp_init);
diff --git a/kernel/module.c b/kernel/module.c
index 0bd0077..e22d020 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -53,6 +53,7 @@
#include <asm/sections.h>
#include <linux/tracepoint.h>
#include <linux/ftrace.h>
+#include <linux/livepatch.h>
#include <linux/async.h>
#include <linux/percpu.h>
#include <linux/kmemleak.h>
@@ -984,6 +985,7 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
mod->exit();
blocking_notifier_call_chain(&module_notify_list,
MODULE_STATE_GOING, mod);
+ klp_module_going(mod);
ftrace_release_mod(mod);

async_synchronize_full();
@@ -3315,6 +3317,7 @@ fail:
module_put(mod);
blocking_notifier_call_chain(&module_notify_list,
MODULE_STATE_GOING, mod);
+ klp_module_going(mod);
ftrace_release_mod(mod);
free_module(mod);
wake_up_all(&module_wq);
@@ -3371,12 +3374,17 @@ out_unlocked:

static int prepare_coming_module(struct module *mod)
{
+ int err;

ftrace_module_enable(mod);
+ err = klp_module_coming(mod);
+ if (err)
+ return err;

blocking_notifier_call_chain(&module_notify_list,
MODULE_STATE_COMING, mod);
return 0;
+
}

static int complete_formation(struct module *mod, struct load_info *info)
@@ -3556,6 +3564,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
mod->state = MODULE_STATE_GOING;
blocking_notifier_call_chain(&module_notify_list,
MODULE_STATE_GOING, mod);
+ klp_module_going(mod);

bug_cleanup:
/* module_bug_cleanup needs module_mutex protection */
--
2.4.3
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