linux-kernel - Re: [RFC PATCH v3 4/6] livepatch: reuse module loader code to write relocations

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Message-ID: <alpine.LNX.2.00.1601131012340.10011@pobox.suse.cz>
Date:	Wed, 13 Jan 2016 10:19:30 +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 v3 4/6] livepatch: reuse module loader code to write
 relocations

On Fri, 8 Jan 2016, Jessica Yu wrote:

>  static int klp_write_object_relocations(struct module *pmod,
>  					struct klp_object *obj)
>  {
> -	int ret = 0;
> -	unsigned long val;
> -	struct klp_reloc *reloc;
> +	int i, len, ret = 0;
> +	char *secname;
> +	const char *objname;
>  
>  	if (WARN_ON(!klp_is_object_loaded(obj)))
>  		return -EINVAL;
>  
> -	if (WARN_ON(!obj->relocs))
> -		return -EINVAL;
> +	objname = klp_is_module(obj) ? obj->name : "vmlinux";
>  
>  	module_disable_ro(pmod);
> +	/* For each klp rela section for this object */
> +	for (i = 1; i < pmod->info->hdr->e_shnum; i++) {
> +		if (!(pmod->info->sechdrs[i].sh_flags & SHF_RELA_LIVEPATCH))
> +			continue;

One more thing. If the module does not specify it is a live patch module 
in modinfo (with MODULE_INFO(livepatch, "Y")), but it is a perfect live 
patch module otherwise (it calls klp_register_patch in its init function), 
the kernel crashes here. pmod->info is not initialized at all. This should 
be fixed. Perhaps the easiest would be to call 
klp_write_object_relocations() in klp_init_object_loaded() only if 
is_livepatch_module() returns true. Similar to a check for obj->relocs 
before.

Miroslav