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. --Andy
