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

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Message-ID: <20151130204617.GB7648@canonical.com>
Date:	Mon, 30 Nov 2015 14:46:18 -0600
From:	Chris J Arges <chris.j.arges@...onical.com>
To:	Miroslav Benes <mbenes@...e.cz>
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 Mon, Nov 23, 2015 at 10:52:23AM +0100, Miroslav Benes wrote:
> 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
>

Yes I need to fix this, an option would be to use:
	ret = klp_find_object_symbol(obj->name ? obj->name : obj->mod->name,
				     reloc->name, 0, &reloc->val);

Testing with kpatch will require some modifications as the structures are
different.

--chris
--
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