linux-kernel - Re: [PATCH 1/3] module: Fix livepatch/ftrace module text permissions race

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Date:   Fri, 14 Jun 2019 17:04:08 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Jessica Yu <jeyu@...nel.org>, Petr Mladek <pmladek@...e.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
        Johannes Erdfelt <johannes@...felt.com>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 1/3] module: Fix livepatch/ftrace module text
 permissions race

On Thu, 13 Jun 2019 20:07:22 -0500
Josh Poimboeuf <jpoimboe@...hat.com> wrote:

> It's possible for livepatch and ftrace to be toggling a module's text
> permissions at the same time, resulting in the following panic:
> 

[..]

> The above panic occurs when loading two modules at the same time with
> ftrace enabled, where at least one of the modules is a livepatch module:
> 
> CPU0					CPU1
> klp_enable_patch()
>   klp_init_object_loaded()
>     module_disable_ro()
>     					ftrace_module_enable()
> 					  ftrace_arch_code_modify_post_process()
> 				    	    set_all_modules_text_ro()
>       klp_write_object_relocations()
>         apply_relocate_add()
> 	  *patches read-only code* - BOOM
> 
> A similar race exists when toggling ftrace while loading a livepatch
> module.
> 
> Fix it by ensuring that the livepatch and ftrace code patching
> operations -- and their respective permissions changes -- are protected
> by the text_mutex.
> 
> Reported-by: Johannes Erdfelt <johannes@...felt.com>
> Fixes: 444d13ff10fb ("modules: add ro_after_init support")
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> Acked-by: Jessica Yu <jeyu@...nel.org>
> Reviewed-by: Petr Mladek <pmladek@...e.com>
> Reviewed-by: Miroslav Benes <mbenes@...e.cz>

This patch looks uncontroversial. I'm going to pull this one in and
start testing it. And if it works, I'll push to Linus.

-- Steve