Re: [PATCH 12/23] x86, kaiser: map dynamically-allocated LDTs

[Ingo Molnar]

* Andy Lutomirski <luto@xxxxxxxxxx> wrote:

> On Tue, Oct 31, 2017 at 3:32 PM, Dave Hansen
> <dave.hansen@xxxxxxxxxxxxxxx> wrote:
> >
> > Normally, a process just has a NULL mm->context.ldt.  But, we
> > have a syscall for a process to set a new one.  If a process does
> > that, we need to map the new LDT.
> >
> > The original KAISER patch missed this case.
> 
> Tglx suggested that we instead increase the padding at the top of the
> user address space from 4k to 64k and put the LDT there.  This is a
> slight ABI break, but I'd be rather surprised if anything noticed,
> especially because the randomized vdso currently regularly lands there
> (IIRC), so any user code that explicitly uses those 60k already
> collides with the vdso.
> 
> I can make this happen.

Yes, let's try that.

Thanks,

	Ingo