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Message-ID: <50CBBACA.2070108@linaro.org>
Date: Fri, 14 Dec 2012 15:48:26 -0800
From: John Stultz <john.stultz@linaro.org>
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To: "H. Peter Anvin" <hpa@zytor.com>
CC: Cyrill Gorcunov <gorcunov@openvz.org>,
        Andy Lutomirski <luto@amacapital.net>, aarcange@redhat.com,
        ak@linux.intel.com, Pavel Emelyanov <xemul@parallels.com>,
        Stefani Seibold <stefani@seibold.net>, x86@kernel.org,
        linux-kernel@vger.kernel.org, criu@openvz.org, mingo@redhat.com,
        tglx@linutronix.de
Subject: Re: [CRIU] [PATCH] Add VDSO time function support for x86 32-bit
 kernel
References: <50CAE485.5020608@parallels.com> <50CB716D.6020501@zytor.com> <CALCETrWazriQVbQPc8u+KFyNUaa=kJUc=jdh9w7z6rS+kWEX1w@mail.gmail.com> <50CB7459.7010107@zytor.com> <20121214201217.GE6582@moon> <50CB9553.7050808@zytor.com> <CALCETrUS7JDtLd0jYy7cRNoBm1VHhMw3sTPRjhsm3uDwoPQrCA@mail.gmail.com> <50CBA171.4080403@zytor.com> <20121214222517.GG6582@moon> <50CBA7BC.4020001@zytor.com> <20121214224307.GH6582@moon> <50CBACD2.60307@zytor.com>
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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