linux-kernel - Re: [CRIU] [PATCH] Add VDSO time function support for x86 32-bit kernel

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Date:	Fri, 14 Dec 2012 10:47:53 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Pavel Emelyanov <xemul@...allels.com>, aarcange@...hat.com,
	ak@...ux.intel.com, Stefani Seibold <stefani@...bold.net>,
	x86@...nel.org, linux-kernel@...r.kernel.org, criu@...nvz.org,
	mingo@...hat.com, john.stultz@...aro.org, tglx@...utronix.de
Subject: Re: [CRIU] [PATCH] Add VDSO time function support for x86 32-bit
 kernel

On 12/14/2012 10:44 AM, Andy Lutomirski wrote:
>>
>> mremap() should work.  At the same time, the code itself is not going to
>> have any stability guarantees between kernel versions -- it obviously
>> cannot.
> 
> We could guarantee that the symbols in the vdso resolve to particular
> offsets within the vdso.  (Yes, this is ugly.)
> 
> Does criu support checkpointing with one version of a shared library
> and restoring with another?  If there are no textrels (or whatever the
> relocation type that actually modifies text as opposed to just the plt
> or got) then, in principle, it should be doable.  Otherwise some
> kernel help will be needed to checkpoint reliably on one kernel and
> restore somewhere else.
> 
> (This isn't a regression -- it's already broken.)
> 

The real issue is that happens if the process is checkpointed while
inside the vdso and now eip/rip or a stack frame points into the vdso.
This is not impossible or even unlikely, especially on 32 bits it is
downright likely.

	-hpa

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