linux-kernel - Re: [RFC PATCH v2 3/6] module: s390: keep mod_arch

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Date:	Wed, 16 Dec 2015 13:02:32 +0100 (CET)
From:	Miroslav Benes <mbenes@...e.cz>
To:	Jessica Yu <jeyu@...hat.com>
cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Kosina <jikos@...nel.org>,
	Vojtech Pavlik <vojtech@...e.com>,
	Jonathan Corbet <corbet@....net>, linux-api@...r.kernel.org,
	live-patching@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	linux-doc@...r.kernel.org
Subject: Re: [RFC PATCH v2 3/6] module: s390: keep mod_arch_specific for
 livepatch modules

On Mon, 30 Nov 2015, Jessica Yu wrote:

> Livepatch needs to utilize the symbol information contained in the
> mod_arch_specific struct in order to be able to call the s390
> apply_relocate_add() function to apply relocations. Remove the redundant
> vfree() in module_finalize() since module_arch_freeing_init() (which also frees
> said structures) is called in do_init_module(). Keep a reference to syminfo if
> the module is a livepatch module and free the structures in
> module_arch_cleanup(). If the module isn't a livepatch module, we free the
> structures in module_arch_freeing_init() as usual.
> 
> Signed-off-by: Jessica Yu <jeyu@...hat.com>
> ---
>  arch/s390/kernel/module.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/s390/kernel/module.c b/arch/s390/kernel/module.c
> index 0c1a679..17a1979 100644
> --- a/arch/s390/kernel/module.c
> +++ b/arch/s390/kernel/module.c
> @@ -51,6 +51,9 @@ void *module_alloc(unsigned long size)
>  
>  void module_arch_freeing_init(struct module *mod)
>  {
> +	if (mod->klp)
> +		return;
> +
>  	vfree(mod->arch.syminfo);
>  	mod->arch.syminfo = NULL;
>  }

Hm, this is problematic. module_arch_freeing_init() is called from 
module_deallocate() and this is called in the error path in load_module(). 
So if there was an error during load_module() of livepatch module which 
led to free_modinfo label or behind mod->arch.syminfo would not be freed 
at all. module_arch_cleanup() is called earlier under 
free_arch_cleanup.

Miroslav

> @@ -420,12 +423,18 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
>  	return 0;
>  }
>  
> +void module_arch_cleanup(struct module *mod)
> +{
> +	if (mod->klp) {
> +		vfree(mod->arch.syminfo);
> +		mod->arch.syminfo = NULL;
> +	}
> +}
> +
>  int module_finalize(const Elf_Ehdr *hdr,
>  		    const Elf_Shdr *sechdrs,
>  		    struct module *me)
>  {
>  	jump_label_apply_nops(me);
> -	vfree(me->arch.syminfo);
> -	me->arch.syminfo = NULL;
>  	return 0;
>  }
> -- 
> 2.4.3
> 

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