From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1764531AbYETLjg (ORCPT ); Tue, 20 May 2008 07:39:36 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752971AbYETLj2 (ORCPT ); Tue, 20 May 2008 07:39:28 -0400 Received: from bzq-179-150-194.static.bezeqint.net ([212.179.150.194]:56014 "EHLO il.qumranet.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752557AbYETLj2 (ORCPT ); Tue, 20 May 2008 07:39:28 -0400 From: Avi Kivity To: Andrew Morton Cc: Ingo Molnar , Andi Kleen , linux-kernel@vger.kernel.org, Sam Ravnborg Subject: [PATCH] Make LIST_POISON less deadly (v3) Date: Tue, 20 May 2008 14:39:25 +0300 Message-Id: <1211283565-30671-1-git-send-email-avi@qumranet.com> X-Mailer: git-send-email 1.5.5.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The list macros use LIST_POISON1 and LIST_POISON2 as undereferencable pointers in order to trap erronous use of freed list_heads. Unfortunately userspace can arrange for those pointers to actually be dereferencable, potentially turning an oops to an expolit. To avoid this allow architectures (currently x86_64 only) to override the default values for these pointers with truly-undereferncable values. This is easy on x86_64 as the virtual address space is large and contains unmapped ranges. Signed-off-by: Avi Kivity --- Changes since v1: - add CONFIG_ILLEGAL_POINTER_VALUE instead of new header Changes since v2: - switched the range from an uncanonical address to a canonical unmapped address, since uncannonical addresses generate #GP instead of #PF, losing the faulting address. arch/x86/Kconfig | 5 +++++ include/linux/poison.h | 10 ++++++++-- 2 files changed, 13 insertions(+), 2 deletions(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index fe361ae..54d4e36 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -1021,6 +1021,11 @@ config ARCH_MEMORY_PROBE def_bool X86_64 depends on MEMORY_HOTPLUG +config ILLEGAL_POINTER_VALUE + hex + default 0 if X86_32 + default 0xffffc10000000000 if X86_64 + source "mm/Kconfig" config HIGHPTE diff --git a/include/linux/poison.h b/include/linux/poison.h index 9f31683..0d105a5 100644 --- a/include/linux/poison.h +++ b/include/linux/poison.h @@ -1,14 +1,20 @@ #ifndef _LINUX_POISON_H #define _LINUX_POISON_H +#ifdef CONFIG_ILLEGAL_POINTER_VALUE +#define POISON_POINTER_DELTA CONFIG_ILLEGAL_POINTER_VALUE +#else +#define POISON_POINTER_DELTA 0L +#endif + /********** include/linux/list.h **********/ /* * These are non-NULL pointers that will result in page faults * under normal circumstances, used to verify that nobody uses * non-initialized list entries. */ -#define LIST_POISON1 ((void *) 0x00100100) -#define LIST_POISON2 ((void *) 0x00200200) +#define LIST_POISON1 ((void *) 0x00100100 + POISON_POINTER_DELTA) +#define LIST_POISON2 ((void *) 0x00200200 + POISON_POINTER_DELTA) /********** include/linux/timer.h **********/ /* -- 1.5.5.1