Date: Fri, 18 Nov 2016 09:55:08 -0800 From: Kees Cook <keescook@...omium.org> To: Christoph Lameter <cl@...ux.com> Cc: Michael Ellerman <mpe@...erman.id.au>, Andrew Morton <akpm@...ux-foundation.org>, Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com> Subject: Re: [PATCH v2] slab: Add POISON_POINTER_DELTA to ZERO_SIZE_PTR On Fri, Nov 18, 2016 at 9:47 AM, Christoph Lameter <cl@...ux.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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