linux-kernel - Re: Pondering per-process vsyscall disablement

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Message-ID: <5388E814.1080504@zytor.com>
Date:	Fri, 30 May 2014 13:20:36 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Marian Marinov <mm@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Linux API <linux-api@...r.kernel.org>
Subject: Re: Pondering per-process vsyscall disablement

On 05/30/2014 01:11 PM, Andy Lutomirski wrote:
> On Fri, May 30, 2014 at 1:05 PM, H. Peter Anvin <hpa@...or.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


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