Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753699AbcKQJva (ORCPT ); Thu, 17 Nov 2016 04:51:30 -0500 Received: from ozlabs.org ([103.22.144.67]:39137 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750813AbcKQJv0 (ORCPT ); Thu, 17 Nov 2016 04:51:26 -0500 From: Michael Ellerman To: akpm@linux-foundation.org Cc: cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com, keescook@chromium.org Subject: [PATCH v2] slab: Add POISON_POINTER_DELTA to ZERO_SIZE_PTR Date: Thu, 17 Nov 2016 20:51:07 +1100 Message-Id: <1479376267-18486-1-git-send-email-mpe@ellerman.id.au> X-Mailer: git-send-email 2.7.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1588 Lines: 50 POISON_POINTER_DELTA is defined in poison.h, and is intended to be used to shift poison values so that they don't alias userspace. We should add it to ZERO_SIZE_PTR so that attackers can't use ZERO_SIZE_PTR as a way to get a non-NULL pointer to userspace. 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. 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). Signed-off-by: Michael Ellerman --- include/linux/slab.h | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) v2: Rework ZERO_OR_NULL_PTR() to do the two checks separately. diff --git a/include/linux/slab.h b/include/linux/slab.h index 084b12bad198..404419d9860f 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -12,6 +12,7 @@ #define _LINUX_SLAB_H #include +#include #include #include @@ -109,10 +110,13 @@ * ZERO_SIZE_PTR can be passed to kfree though in the same way that NULL can. * Both make kfree a no-op. */ -#define ZERO_SIZE_PTR ((void *)16) +#define ZERO_SIZE_PTR ((void *)(16 + POISON_POINTER_DELTA)) -#define ZERO_OR_NULL_PTR(x) ((unsigned long)(x) <= \ - (unsigned long)ZERO_SIZE_PTR) +#define ZERO_OR_NULL_PTR(x) \ + ({ \ + void *p = (void *)(x); \ + (p == NULL || p == ZERO_SIZE_PTR); \ + }) #include #include -- 2.7.4