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

From: Ingo Molnar
Date: Wed Jul 13 2016 - 03:56:45 EST

* 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!