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Date: Wed, 13 Jan 2016 10:19:30 +0100 (CET)
From: Miroslav Benes <mbenes@suse.cz>
To: Jessica Yu <jeyu@redhat.com>
cc: Rusty Russell <rusty@rustcorp.com.au>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Seth Jennings <sjenning@redhat.com>, Jiri Kosina <jikos@kernel.org>,
        Vojtech Pavlik <vojtech@suse.com>, Jonathan Corbet <corbet@lwn.net>,
        linux-api@vger.kernel.org, live-patching@vger.kernel.org,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        linux-s390@vger.kernel.org, linux-doc@vger.kernel.org
Subject: Re: [RFC PATCH v3 4/6] livepatch: reuse module loader code to write
 relocations
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References: <1452281304-28618-1-git-send-email-jeyu@redhat.com> <1452281304-28618-5-git-send-email-jeyu@redhat.com>
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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