linux-kernel - Re: [PATCH][v4] livepatch/ppc: Enable livepatching on powerpc

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20160304192222.GA31341@lst.de>
Date:	Fri, 4 Mar 2016 20:22:22 +0100
From:	Torsten Duwe <duwe@....de>
To:	Petr Mladek <pmladek@...e.com>
Cc:	jeyu@...hat.com, jkosina@...e.cz, linux-kernel@...r.kernel.org,
	rostedt@...dmis.org, kamalesh@...ux.vnet.ibm.com,
	linuxppc-dev@...abs.org, live-patching@...r.kernel.org,
	mbenes@...e.cz
Subject: Re: [PATCH][v4] livepatch/ppc: Enable livepatching on powerpc

On Fri, Mar 04, 2016 at 07:16:57PM +0100, Torsten Duwe wrote:
> On Fri, Mar 04, 2016 at 02:01:37PM +0100, Petr Mladek wrote:
> > 
> > Do I understand it correctly that we could not patch functions that
> > pass arguments on the stack with this implementation? If yes, how hard
> > would be to get it working, please? At least, it would be great to
> > catch this problem and handle it with grace. Otherwise, it might
> > be hard to debug.
> 
> No, those functions only require special attention.

So far it's correct. It's been a while since I wrote that code.

> I needed _any_ location to store the caller's TOC;
> and the stack is thread-safe and recursion-safe.
> The current caller's frame is already full so I had
> to create a new one.

Correction: the TOC can be stored in the caller's stack frame at
the usual location. Only the restore instruction is a problem.

> A patch function could e.g. grab that TOC value in a
> prologue and then pop that stack frame. Or it could
> add those 32 bytes to the assumed arguments' stack offsets.

So one solution could be to call the patch function via a small
trampoline or pre-prologue that just pops that frame, and have
the patch function restore R2 manually at the end.

Sorry for the confusion,

	Torsten