linux-kernel - Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack

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Message-ID: <20160819215522.ofav5ifdn7i5taxm@treble>
Date:   Fri, 19 Aug 2016 16:55:22 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Brian Gerst <brgerst@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Byungchul Park <byungchul.park@....com>,
        Nilay Vaish <nilayvaish@...il.com>
Subject: Re: [PATCH v4 54/57] x86/mm: convert arch_within_stack_frames() to
 use the new unwinder

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@...hat.com> 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@...hat.com>
> 
> 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