linux-kernel - Re: [PATCH][v6][RFC] livepatch/ppc: Enable livepatching on powerpc

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Message-ID: <20160309111647.GA27913@lst.de>
Date:	Wed, 9 Mar 2016 12:16:47 +0100
From:	Torsten Duwe <duwe@....de>
To:	Jiri Kosina <jikos@...nel.org>
Cc:	Petr Mladek <pmladek@...e.com>,
	Balbir Singh <bsingharora@...il.com>, linuxppc-dev@...abs.org,
	linux-kernel@...r.kernel.org, rostedt@...dmis.org,
	kamalesh@...ux.vnet.ibm.com, jeyu@...hat.com,
	live-patching@...r.kernel.org, mbenes@...e.cz
Subject: Re: [PATCH][v6][RFC] livepatch/ppc: Enable livepatching on powerpc

On Wed, Mar 09, 2016 at 11:13:05AM +0100, Jiri Kosina wrote:
> On Wed, 9 Mar 2016, Torsten Duwe wrote:
> > was my first choice. Arguments on the stack? I thought we'll deal with them
> > once we get there (e.g. _really_ need to patch a varargs function or one
> > with a silly signature).
> 
> Well, the problem is, once such need arises, it's too late already.

No, not if it's documented.

> You need to be able to patch the kernels which are already out there, 
> running on machines potentially for ages once all of a sudden there is a 
> CVE for >8args / varargs function.

Then you'd need a solution like I sent out yesterday, with a pre-prologue
caller that pops the extra frame, so the replacement can be more straight-
forward. Or you can just deal with the shifted offsets in the replacement.

I'll try to demonstrate the alternative. That would then be required for
_all_ replacement functions. Or can the live patching framework differentiate
and tell ftrace_caller whether to place a stack frame or not?

Miroslav? Petr? Can we have 2 sorts of replacement functions?

	Torsten