Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to use the new unwinder

[Josh Poimboeuf]

On Fri, Aug 19, 2016 at 11:27:18AM -0700, Kees Cook wrote:
> On Thu, Aug 18, 2016 at 6:06 AM, Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:
> > Convert arch_within_stack_frames() to use the new unwinder.
> >
> > This also changes some existing behavior:
> >
> > - Skip checking of pt_regs frames.
> > - Warn if it can't reach the grandparent's stack frame.
> > - Warn if it doesn't unwind to the end of the stack.
> >
> > Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> 
> All the stuff touching usercopy looks good to me. One question,
> though, in looking through the unwinder. It seems like it's much more
> complex than just the frame-hopping that the old
> arch_within_stack_frames() did, but I'm curious to hear what you think
> about its performance. We'll be calling this with every usercopy that
> touches the stack, so I'd like to be able to estimate the performance
> impact of this replacement...

Yeah, good point.  I'll take some measurements from before and after and
get back to you.

-- 
Josh