linux-kernel - Re: vdso && cr (Was: arch_check_bp_in

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Message-Id: <20121126142655.9AD28592064@miso.sublimeip.com>
Date:	Tue, 27 Nov 2012 01:26:55 +1100 (EST)
From:	u3557@...o.sublimeip.com (Amnon Shiloh)
To:	gorcunov@...nvz.org (Cyrill Gorcunov)
Cc:	avagin@...il.com (Andrey Wagin), oleg@...hat.com (Oleg Nesterov),
	xemul@...allels.com (Pavel Emelyanov),
	rostedt@...dmis.org (Steven Rostedt),
	fweisbec@...il.com (Frederic Weisbecker),
	mingo@...hat.com (Ingo Molnar),
	a.p.zijlstra@...llo.nl (Peter Zijlstra),
	linux-kernel@...r.kernel.org (LKML)
Subject: Re: vdso && cr (Was: arch_check_bp_in_kernelspace: fix the range

Hi Cyrill,

Programmers don't (and the manual-page says they shouldn't even try)
call "sigreturn" directly.

If an interrupt happens, by bad luck, to occur while the process
is running vdso code, then eventually, once signal-processing is
complete, "sigreturn" (issued by  glibc) will take the process back
to where it was before the interrupt happend, inside the vdso page.

Best Regards,
Amnon.

> On Mon, Nov 26, 2012 at 11:55:01PM +1100, Amnon Shiloh wrote:
> > 
> > You could of course keep that old code and modify only the very
> > first instruction of each routine into a jump instruction, but then
> > the code to which the process returns may not be compatible with
> > the new kernel and/or hardware configuration.
> 
> For sure there will be some limitations but I fear we can't do
> that much with it. I don't expect the regular program to use
> sigreturn for jumping into vdso code, but I could be wrong.
> 
> 	Cyrill
> 

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