linux-kernel - Re: [PATCH 1/2] livepatch: Add a new function to verify the address and name match for extra module

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Date:	Mon, 13 Apr 2015 12:22:41 +0200
From:	Petr Mladek <pmladek@...e.cz>
To:	Minfei Huang <minfei.huang@...mail.com>
Cc:	jpoimboe@...hat.com, sjenning@...hat.com, jkosina@...e.cz,
	vojtech@...e.cz, live-patching@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] livepatch: Add a new function to verify the address
 and name match for extra module

On Mon 2015-04-13 17:50:23, Minfei Huang wrote:
> On 04/13/15 at 11:41P, Petr Mladek wrote:
> > On Mon 2015-04-13 17:11:19, Minfei Huang wrote:
> > > On 04/13/15 at 10:37P, Petr Mladek wrote:
> > > > On Sun 2015-04-12 21:15:53, Minfei Huang wrote:
> > > > > In order to restrict the patch, we can verify the provided function
> > > > > address and name match. Now we have can only verify the vmlinux function
> > > > > name and address.
> > > > > 
> > > > > Add a new function to verify extra module function name and address. The
> > > > > patch would not be patched, if the function name and address are not
> > > > > matched.
> > > > 
> > > > old_addr could be predefined only for vmlinux. It does not make sense
> > > > to define it for modules because they are loaded dynamically, each
> > > > time on a different addresses. It means that it does not make sense
> > > > to verify addresses from modules. They always need to be detected.
> > > > 
> > > 
> > > Please correct me if there is something wrong for below comment.
> > > 
> > > As commented in the doc that function address is optional, it is more
> > > confortable during patching the patch, if function name and address are
> > > provided.
> > > 
> > > For now we only use function name to detect the module function. It is
> > > more accurate to detect the function using function name and address.
> > 
> > I think that it is the other way. It is easier to create patch without
> > the addresses. It is enough for most patches.
> > 
> > The function address is needed only if there are more functions of
> > the same name. There are only few in vmlinux.
> > 
> > We currently does not allow to handle name conflicts inside a module.
> > But the chance is very small that there will be such a conflict.
> > Do you know about any module that could not be patched because
> > of this?
> > 
> 
> Yes, the function name exceeding to 128 is not happened, in general.
> But I donot think it is the reason that livepatch donot support this
> case.
> 
> Patched these patches, we can still use function name to detect function
> for both vmlinux and extra module.
> 
> It is poisonless that we support to verify both function name and
> address to detect function for extra module.

Please, read my previous mails. We do not know old_addr for modules
at build time. Therefore we could solve this problem easily for
modules.

I think that the whole problem is rather theoretical and it is not
worth spending time on it.

Best Regards,
Petr
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