linux-kernel - Re: [PATCH v2 2/2] livepatch/module: remove livepatch module notifier

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Message-ID: <20160314150643.GU10940@pathway.suse.cz>
Date:	Mon, 14 Mar 2016 16:06:43 +0100
From:	Petr Mladek <pmladek@...e.com>
To:	Jessica Yu <jeyu@...hat.com>
Cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Vojtech Pavlik <vojtech@...e.com>,
	Miroslav Benes <mbenes@...e.cz>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Steven Rostedt <rostedt@...dmis.org>,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] livepatch/module: remove livepatch module notifier

On Fri 2016-03-11 15:03:48, 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.
> 
> Signed-off-by: Jessica Yu <jeyu@...hat.com>
> Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>
> Acked-by: Rusty Russell <rusty@...tcorp.com.au>
> ---
>  include/linux/livepatch.h |  13 ++++
>  kernel/livepatch/core.c   | 147 ++++++++++++++++++++++------------------------
>  kernel/module.c           |  10 ++++
>  3 files changed, 94 insertions(+), 76 deletions(-)
> 
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index 780f00c..4fafbae 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -866,103 +866,108 @@ 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);

One more thing. We should add here:

	mod->klp_alive = true;

Otherwise, there is a small race window when a new patch will try to
patch the module.

>  	klp_free_object_loaded(obj);
> +	mutex_unlock(&klp_mutex);
> +
> +	return ret;
>  }

With the above fix:

Reviewed-by: Petr Mladek <pmladek@...e.cz>


Best Regards,
Petr