Re: Pondering per-process vsyscall disablement

H. Peter Anvin
2014-05-30T20:20:49Z

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