linux-kernel - Re: [PATCH v3 2/2] livepatch/module: remove livepatch module notifier

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Date:	Mon, 8 Feb 2016 15:30:24 +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>,
	Ingo Molnar <mingo@...hat.com>, live-patching@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] livepatch/module: remove livepatch module notifier

On Fri 2016-02-05 22:08:17, 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@...hat.com>
> ---
>  include/linux/livepatch.h |   9 +++
>  kernel/livepatch/core.c   | 153 +++++++++++++++++++++++-----------------------
>  kernel/module.c           |  20 +++++-
>  3 files changed, 103 insertions(+), 79 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..1d47f96 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> +int klp_module_coming(struct module *mod)
[...]
> +			obj->mod = 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;
> +			}
[...]
> +			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;
> +			}
[...]
> +
> +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);
> +	obj->mod = NULL;

To be on the safe side, we should replace this assignment with:

	klp_free_object_loaded(mod);

It clears obj->mod and also all func->old_addr for this module.
By other words, it leaves the structures in the same state as
klp_module_going(). I am sorry that I have missed this before.

Otherwise, it looks fine. So, with the above suggested change:

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

Best Regards,
Petr