From patchwork Thu Nov 17 09:51:07 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Michael Ellerman X-Patchwork-Id: 9433773 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id D6F3860238 for ; Thu, 17 Nov 2016 09:51:43 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C638E29394 for ; Thu, 17 Nov 2016 09:51:43 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B9365293A1; Thu, 17 Nov 2016 09:51:43 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.2 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.wl.linuxfoundation.org (Postfix) with SMTP id EC8F929394 for ; Thu, 17 Nov 2016 09:51:42 +0000 (UTC) Received: (qmail 5600 invoked by uid 550); 17 Nov 2016 09:51:40 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: kernel-hardening@lists.openwall.com Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 5561 invoked from network); 17 Nov 2016 09:51:38 -0000 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 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 Subject: [kernel-hardening] [PATCH v2] slab: Add POISON_POINTER_DELTA to ZERO_SIZE_PTR X-Virus-Scanned: ClamAV using ClamSMTP 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