* Andy Lutomirski <l...@amacapital.net> wrote:
> On Thu, Jul 14, 2016 at 1:07 AM, Ingo Molnar <mi...@kernel.org> wrote:
> >
> > * Andy Lutomirski <l...@amacapital.net> wrote:
> >
> >> On Wed, Jul 13, 2016 at 12:56 AM, Ingo Molnar <mi...@kernel.org> wrote:
> >> >
> >> > * Andy Lutomirski <l...@amacapital.net> wrote:
> >> >
> >> >> > If we push a PKRU value into a thread between the rdpkru() and
> >> >> > wrpkru(), we'll
> >> >> > lose the content of that "push". I'm not sure there's any way to
> >> >> > guarantee
> >> >> > this with a user-controlled register.
> >> >>
> >> >> We could try to insist that user code uses some vsyscall helper that
> >> >> tracks
> >> >> which bits are as-yet-unassigned. That's quite messy, though.
> >> >
> >> > Actually, if we turned the vDSO into something more like a minimal
> >> > user-space
> >> > library with the ability to run at process startup as well to prepare
> >> > stuff
> >> > then it's painful to get right only *once*, and there will be tons of
> >> > other
> >> > areas where a proper per thread data storage on the user-space side
> >> > would be
> >> > immensely useful!
> >>
> >> Doing this could be tricky: how exactly is the vDSO supposed to find
> >> per-thread
> >> data without breaking existing glibc?
> >
> > So I think the way this could be done is by allocating it itself. The vDSO
> > vma
> > itself is 'external' to glibc as well to begin with - this would be a small
> > extension to that concept.
>
> But how does the vdso code find it? FS and GS are both spoken for by
> existing
> userspace.
Minimally relinking itself on a per mm basis?
Thanks,
Ingo
