linux-kernel - Re: [RFC PATCH 3/3] module: pre-test setting ro_after

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Message-ID: <D5HYAAW77P1A.6KLS8F6CVKGS@samsung.com>
Date: Sat, 9 Nov 2024 22:03:06 +0100
From: Daniel Gomez <da.gomez@...sung.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>, Luis Chamberlain
	<mcgrof@...nel.org>, Petr Pavlu <petr.pavlu@...e.com>, Sami Tolvanen
	<samitolvanen@...gle.com>, Kees Cook <kees@...nel.org>,
	<linux-modules@...r.kernel.org>
CC: <linux-kernel@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH 3/3] module: pre-test setting ro_after_init data
 read-only

On Sat Nov 9, 2024 at 11:35 AM CET, Christophe Leroy wrote:
> To be on the safe side, try to set ro_after_init data section readonly
> at the same time as rodata. If it fails it will likely fail again
> later so let's cancel module loading while we still can do it.
> If it doesn't fail, put it back to read-only, continue module loading

I think you mean put it back to rw?

> and cross fingers so that it still works after module init. Then it
> should in principle never fail so add a WARN_ON_ONCE() to get a big
> fat warning in case it happens anyway.

I agree this is the best we can do. But I don't think there's any
guarantee that we won't fail on the second try?

>
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  kernel/module/main.c       | 2 +-
>  kernel/module/strict_rwx.c | 5 ++++-
>  2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index 1bf4b0db291b..b603c9647e73 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -2582,7 +2582,7 @@ static noinline int do_init_module(struct module *mod)
>  	rcu_assign_pointer(mod->kallsyms, &mod->core_kallsyms);
>  #endif
>  	ret = module_enable_rodata_ro_after_init(mod);
> -	if (ret)
> +	if (WARN_ON_ONCE(ret))
>  		pr_warn("%s: %s() returned %d, ro_after_init data might still be writable\n",
>  			mod->name, __func__, ret);
>  
> diff --git a/kernel/module/strict_rwx.c b/kernel/module/strict_rwx.c
> index f68c59974ae2..329afd43f06b 100644
> --- a/kernel/module/strict_rwx.c
> +++ b/kernel/module/strict_rwx.c
> @@ -58,7 +58,10 @@ int module_enable_rodata_ro(const struct module *mod)
>  	if (ret)
>  		return ret;
>  
> -	return 0;
> +	ret = module_set_memory(mod, MOD_RO_AFTER_INIT, set_memory_ro);
> +	if (ret)
> +		return ret;
> +	return module_set_memory(mod, MOD_RO_AFTER_INIT, set_memory_rw);
>  }
>  
>  int module_enable_rodata_ro_after_init(const struct module *mod)