linux-kernel - Re: [PATCH 2/3 v8] livepatch: add sympos as disambiguator field to klp

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Date:	Mon, 23 Nov 2015 10:52:23 +0100 (CET)
From:	Miroslav Benes <mbenes@...e.cz>
To:	Chris J Arges <chris.j.arges@...onical.com>
cc:	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
	jpoimboe@...hat.com, jikos@...nel.org, pmladek@...e.com,
	jeyu@...hat.com, Seth Jennings <sjenning@...hat.com>,
	Vojtech Pavlik <vojtech@...e.com>
Subject: Re: [PATCH 2/3 v8] livepatch: add sympos as disambiguator field to
 klp_reloc

On Fri, 20 Nov 2015, Chris J Arges wrote:

[...]

> @@ -272,6 +233,7 @@ static int klp_write_object_relocations(struct module *pmod,
>  					struct klp_object *obj)
>  {
>  	int ret;
> +	unsigned long val;
>  	struct klp_reloc *reloc;
>  
>  	if (WARN_ON(!klp_is_object_loaded(obj)))
> @@ -281,29 +243,26 @@ static int klp_write_object_relocations(struct module *pmod,
>  		return -EINVAL;
>  
>  	for (reloc = obj->relocs; reloc->name; reloc++) {
> -		if (!klp_is_module(obj)) {
> -			ret = klp_verify_vmlinux_symbol(reloc->name,
> -							reloc->val);
> -			if (ret)
> -				return ret;
> -		} else {
> -			/* module, reloc->val needs to be discovered */
> -			if (reloc->external)
> -				ret = klp_find_external_symbol(pmod,
> -							       reloc->name,
> -							       &reloc->val);
> -			else
> -				ret = klp_find_object_symbol(obj->mod->name,
> -							     reloc->name,
> -							     0, &reloc->val);
> -			if (ret)
> -				return ret;
> -		}
> +		/* discover the address of the referenced symbol */
> +		if (reloc->external) {
> +			if (reloc->sympos > 0) {
> +				pr_err("non-zero sympos for external reloc symbol '%s' is not supported\n",
> +				       reloc->name);
> +				return -EINVAL;
> +			}
> +			ret = klp_find_external_symbol(pmod, reloc->name, &val);
> +		} else
> +			ret = klp_find_object_symbol(obj->mod->name,
> +						     reloc->name,
> +						     reloc->sympos,
> +						     &val);

I think this will cause an unwanted effect if a relocation is for vmlinux 
symbol. obj->mod is NULL in that case. So obj->name should be there. Can 
you test it with kpatch, Chris, please? If that is possible.

Thanks,
Miroslav
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