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Date: Fri, 30 May 2014 13:20:36 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Andy Lutomirski <luto@amacapital.net>
CC: Marian Marinov <mm@1h.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        X86 ML <x86@kernel.org>, Linux API <linux-api@vger.kernel.org>
Subject: Re: Pondering per-process vsyscall disablement
References: <CALCETrX4-qooSyLw3=zHGcMoWqQ2ozPB_WtKU2AtkMei-XZOUA@mail.gmail.com> <537EB60E.40204@1h.com> <CALCETrWgtQCRiHt+am8+DoOMVvTuxy05AB6zzg3iAheGs13L6A@mail.gmail.com> <538658EE.8030809@zytor.com> <CALCETrUhZp+edRCx2SEzuJup0HWhV5WSiheCiZWuUjVueTJHfQ@mail.gmail.com> <5388E499.6080101@zytor.com> <CALCETrX9s7xJRddB26ZiyjMEGbupbDj2qDHhio=80XSQ+staDA@mail.gmail.com>
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On 05/30/2014 01:11 PM, Andy Lutomirski wrote:
> On Fri, May 30, 2014 at 1:05 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>> On 05/30/2014 01:00 PM, Andy Lutomirski wrote:
>>>
>>> Do the flags go in the ELF loader or in the executable we're running?
>>> Or both (and, if both, do we and them or or them)?
>>>
>>> I think the interpreter makes a little more sense in general: for the
>>> most part, use of vsyscalls is a property of the runtime environment,
>>> not of the program being run.  But maybe this is naive.
>>>
>>
>> They go into each object which becomes part of the running program, i.e.
>> executable, dynamic libraries, and dynamic linker.
> 
> Well, sure, but the kernel is not about to start reading ELF headers
> in dynamic libraries.  So we need to make a decision based on the
> interpreter and the executable.  The conservative approach is to
> require both to have the flag set *and* to offer a prctl to twiddle
> the flags.  Then userspace loaders can do whatever they want, and
> distros get to rebuild the world :)
> 

Yes, something like that.

	-hpa