Re: Pondering per-process vsyscall disablement

Andy Lutomirski
2014-05-30T20:36:12Z

On Fri, May 30, 2014 at 1:20 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> 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.

I'll hack something up once the merge window closes. Or maybe sooner
if you commit my vsyscall patches from a few days ago. Otherwise I'm
just going to confuse my git tree too much :)

--Andy

>
> -hpa
>
>
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--
Andy Lutomirski
AMA Capital Management, LLC