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

From: Torsten Duwe
Date: Wed Mar 09 2016 - 06:17:01 EST

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?