From: Kees Cook <keescook@chromium.org>
To: Christoph Lameter <cl@linux.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>,
Andrew Morton <akpm@linux-foundation.org>,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
"kernel-hardening@lists.openwall.com"
<kernel-hardening@lists.openwall.com>
Subject: Re: [PATCH v2] slab: Add POISON_POINTER_DELTA to ZERO_SIZE_PTR
Date: Fri, 18 Nov 2016 09:55:08 -0800 [thread overview]
Message-ID: <CAGXu5jKC8XTP=gjCGQYEEwSQEAWM66E8HedaEqZR3F=QSm+aTg@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1611181146330.26818@east.gentwo.org>
On Fri, Nov 18, 2016 at 9:47 AM, Christoph Lameter <cl@linux.com> wrote:
> On Thu, 17 Nov 2016, Michael Ellerman wrote:
>
>> Currently ZERO_OR_NULL_PTR() uses a trick of doing a single check that
>> x <= ZERO_SIZE_PTR, and ignoring the fact that it also matches 1-15.
>
> Well yes that was done so we do not add too many branches all over the
> kernel.....
There are actually very few callers of this macro. (Though it's
possible they're executed frequently.)
>> That no longer really works once we add the poison delta, so split it
>> into two checks. Assign x to a temporary to avoid evaluating it
>> twice (suggested by Kees Cook).
>
> And now you are doing just that.
In this case, what about the original < ZERO_SIZE_PTR check Michael
suggested? At least the one use in usercopy.c needs to be fixed, but
otherwise, it should be fine?
-Kees
--
Kees Cook
Nexus Security
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next prev parent reply other threads:[~2016-11-18 17:55 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-17 9:51 Michael Ellerman
2016-11-17 20:01 ` Kees Cook
2016-11-18 17:47 ` Christoph Lameter
2016-11-18 17:55 ` Kees Cook [this message]
2016-11-18 18:19 ` Christoph Lameter
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