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

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Date:	Fri, 14 Dec 2012 15:48:26 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Andy Lutomirski <luto@...capital.net>, aarcange@...hat.com,
	ak@...ux.intel.com, Pavel Emelyanov <xemul@...allels.com>,
	Stefani Seibold <stefani@...bold.net>, x86@...nel.org,
	linux-kernel@...r.kernel.org, criu@...nvz.org, mingo@...hat.com,
	tglx@...utronix.de
Subject: Re: [CRIU] [PATCH] Add VDSO time function support for x86 32-bit
 kernel

On 12/14/2012 02:48 PM, H. Peter Anvin wrote:
> On 12/14/2012 02:43 PM, Cyrill Gorcunov wrote:
>> On Fri, Dec 14, 2012 at 02:27:08PM -0800, H. Peter Anvin wrote:
>>
>>
>> This won't help in case of scenario you've been pointing in
>> previous email (where c/r happens in a middle of vdso),
>> would it? Because we still need somehow to be sure we're not
>> checkpointing in a middle of signal handler which will return
>> to some vdso place.
> It is okay if and only if those vdso places never change... which I
> think is doable if they only contain trival system call wrappers, i.e.
> something like:
>
> 	movl $__SYS_gettimeofday, %eax
> 	syscall
> 	ret

Though doesn't this make it easier for exploits (somewhat undoing ASLR)? 
I know Andi always wanted to avoid having syscall instructions at a 
fixed location for the old vsyscall code (though I know we had it 
none-the-less for awhile).   But maybe I'm confusing issues here?

thanks
-john
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