Re: [PATCH 0/3] ABI CHANGE!!! Remove questionable remote SP reads

[Raymond Jennings]

My personal opinion is that even looking at esp/rsp is asking for 
trouble.  The only reliable information is VM_STACK or another VM flag 
that makes the area expand in response to stack growth.

Besides, userspace could always play funky trampoline games with the 
stack pointer, or even dynamically expand the stack by doing a malloc 
if a stack overflow draws near, which would put the stack in the data 
section temporarily.

As long as esp is in the bounds of a valid VMA, my vote is that we 
should consider it undefined how the task uses it.

On Mon, Oct 3, 2016 at 4:17 PM, Linus Torvalds 
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, Oct 3, 2016 at 4:08 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> 
> wrote:
> >  Ping!
> >
> >  We need to decide fairly soon whether to apply these (or perhaps 
> > just
> >  patch 1 or just patches 2 and 3) for 4.9.  For any parts that aren't
> >  applied, I'll send quick fixups to pin the stack in the offending
> >  code.
>
> I think we should apply it. Hopefully nothing uses it, and nobody will
> notice. And if somebody *does* notice, the sooner we find out, the
> better.
>
>              Linus