* Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > On Thu, Jul 14, 2016 at 1:07 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote: > > > > * Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > > > >> On Wed, Jul 13, 2016 at 12:56 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote: > >> > > >> > * Andy Lutomirski <luto@xxxxxxxxxxxxxx> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
