# Re: \[PATCH 6/9\] x86, pkeys: add pkey set/get syscalls

- From: Ingo Molnar \<mingo@kernel.org\>
- Date: 2016-07-14 08:07:18 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2016/07/4794705
- Thread: https://ratatoskr.run/linux-api/2016/07/4790123/t.md

```text

* Andy Lutomirski [ref] wrote:

> On Wed, Jul 13, 2016 at 12:56 AM, Ingo Molnar [ref] wrote:
> >
> > * Andy Lutomirski [ref] 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.

Thanks,

	Ingo
```