linux-kernel - Re: [PATCH 2/2] livepatch: Fix the bug if the function name is larger than KSYM_NAME

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Message-ID: <20150414162718.GC21044@dhcp128.suse.cz>
Date:	Tue, 14 Apr 2015 18:27:18 +0200
From:	Petr Mladek <pmladek@...e.cz>
To:	Minfei Huang <minfei.huang@...mail.com>
Cc:	Josh Poimboeuf <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 2/2] livepatch: Fix the bug if the function name is
 larger than KSYM_NAME_LEN-1

On Tue 2015-04-14 23:55:36, Minfei Huang wrote:
> On 04/14/15 at 10:11P, Josh Poimboeuf wrote:
> > On Tue, Apr 14, 2015 at 01:45:49PM +0800, Minfei Huang wrote:
> > > On 04/14/15 at 12:32P, Josh Poimboeuf wrote:
> > > > On Tue, Apr 14, 2015 at 01:29:50PM +0800, Minfei Huang wrote:
> > > > > 
> > > > > For end user, they may know litter about restriction of kallsyms and
> > > > > livepatch. How can they know the restriction that function name is
> > > > > limited to 127?
> > > > 
> > > > As I mentioned above, I think kallsyms.c should fail the build if it
> > > > encounters a symbol longer than KSYM_NAME_LEN.
> > > > 
> > > 
> > > I dont think it is a good idea to handle this case like that. The
> > > function name is only for human recognization. Why the compiler fails
> > > to build it?
> > 
> > Well, the function name isn't only for human recognition.  kpatch-build
> > generates patch modules automatically.  It assumes that the compiled
> > function name matches the kallsyms name.  And I'd guess that a lot of
> > other code (both in-kernel and user space tools) make the same
> > assumption.
> > 
> > Not to mention that most humans would also make the same assumption...
> 
> Yes. The assumption is correct for most case.
> 
> It is significance for livepatch to support extra module, because in my
> opinion kernel is more stable than the third module.
> 
> So it is more important, if the livepatch can patch all sorts of patch.
> For dynamic function name, I think it is simple to avoid it.

Do you have some really existing module with such a crazy long
function names or is this debate pure theoretical, please?

Also have you tested your patch and tried to apply livepatch
for some really exiting module, please? I ask because it won't
be trivial to create such a patch. Also the patch would work
only for the one running system.

Best Regards,
Petr

> Usually, we will use ominity to handle a bunch of machines. So it is
> simple, if we use script to get the function address and build the patch.  
> 
> Josh, is there any chance to accept my patches? It may be important
> somewhile that system can not restart without schedule to reload the
> fixed-module.
> 
> Thanks
> Minfei
> 
> > 
> > -- 
> > Josh
> --
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