Re: [PATCH v4 4/4] livepatch/module: remove livepatch module notifier

[Josh Poimboeuf <jpoimboe@redhat.com>]

On Mon, Feb 08, 2016 at 11:50:24PM -0500, Jessica Yu wrote:
> 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>

Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>

> ---
>  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
> 

-- 
Josh