linux-kernel - Re: [PATCH v4 15/16] module: Move where we mark modules RO,X

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Date:   Mon, 21 Oct 2019 08:53:12 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, rostedt@...dmis.org,
        mhiramat@...nel.org, bristot@...hat.com, jbaron@...mai.com,
        torvalds@...ux-foundation.org, tglx@...utronix.de,
        mingo@...nel.org, namit@...are.com, hpa@...or.com, luto@...nel.org,
        ard.biesheuvel@...aro.org, jeyu@...nel.org
Subject: Re: [PATCH v4 15/16] module: Move where we mark modules RO,X

On Fri, Oct 18, 2019 at 09:35:40AM +0200, Peter Zijlstra wrote:
> Now that set_all_modules_text_*() is gone, nothing depends on the
> relation between ->state = COMING and the protection state anymore.
> This enables moving the protection changes later, such that the COMING
> notifier callbacks can more easily modify the text.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Cc: Jessica Yu <jeyu@...nel.org>
> ---
>  kernel/module.c |    8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -3683,10 +3683,6 @@ static int complete_formation(struct mod
>  	/* This relies on module_mutex for list integrity. */
>  	module_bug_finalize(info->hdr, info->sechdrs, mod);
>  
> -	module_enable_ro(mod, false);
> -	module_enable_nx(mod);
> -	module_enable_x(mod);
> -
>  	/* Mark state as coming so strong_try_module_get() ignores us,
>  	 * but kallsyms etc. can see us. */
>  	mod->state = MODULE_STATE_COMING;
> @@ -3852,6 +3848,10 @@ static int load_module(struct load_info
>  	if (err)
>  		goto bug_cleanup;
>  
> +	module_enable_ro(mod, false);
> +	module_enable_nx(mod);
> +	module_enable_x(mod);
> +
>  	/* Module is ready to execute: parsing args may do that. */
>  	after_dashes = parse_args(mod->name, mod->args, mod->kp, mod->num_kp,
>  				  -32768, 32767, mod,

[ Sorry if this was already discussed, I still have a large backlog. ]

Doesn't livepatch code also need to be modified?  We have:

prepare_coming_module()
	klp_module_coming()
		klp_init_object_loaded()
			module_disable_ro()
			...
			module_enable_ro()

which is done right before the above patch does module_enable_ro().

We could remove the disable-RO from that case, though we'd still need it
for another case (late module patching).

-- 
Josh