Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762851Ab3DDVAw (ORCPT ); Thu, 4 Apr 2013 17:00:52 -0400 Received: from mail-ie0-f175.google.com ([209.85.223.175]:51629 "EHLO mail-ie0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762183Ab3DDVAv (ORCPT ); Thu, 4 Apr 2013 17:00:51 -0400 MIME-Version: 1.0 In-Reply-To: References: <1365106055-22939-1-git-send-email-keescook@chromium.org> <1365106055-22939-4-git-send-email-keescook@chromium.org> <515DDEC0.9000109@zytor.com> Date: Thu, 4 Apr 2013 14:00:50 -0700 Message-ID: Subject: Re: [PATCH 3/3] x86: kernel base offset ASLR From: Julien Tinnes To: "H. Peter Anvin" Cc: Kees Cook , LKML , "kernel-hardening@lists.openwall.com" , Thomas Gleixner , Ingo Molnar , "x86@kernel.org" , Jarkko Sakkinen , Matthew Garrett , Matt Fleming , Eric Northup , Dan Rosenberg , Will Drewry Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2360 Lines: 54 Natural evolution: when the cluster is the computer, kernel panics are recoverable like segfaults in a multi-process OS. You have a point and 8 bits isn't perfect, but it's already useful regardless, in certain scenarios. On Thu, Apr 4, 2013 at 1:58 PM, H. Peter Anvin wrote: > It seems to me that you are assuming that the attacker is targeting a specific system, but a bot might as well target 256 different systems and see what sticks... > > Kees Cook wrote: > >>On Thu, Apr 4, 2013 at 1:12 PM, H. Peter Anvin wrote: >>> On 04/04/2013 01:07 PM, Kees Cook wrote: >>>> However, the benefits of >>>> this feature in certain environments exceed the perceived >>weaknesses[2]. >>> >>> Could you clarify? >> >>I would summarize the discussion of KASLR weaknesses into to two >>general observations: >>1- it depends on address location secrecy and leaks are common/easy. >>2- it has low entropy so attack success rates may be high. >> >>For "1", as Julien mentions, remote attacks and attacks from a >>significantly contained process (via seccomp-bpf) minimizes the leak >>exposure. For local attacks, cache timing attacks and other things >>also exist, but the ASLR can be improved to defend against that too. >>So, KASLR is useful on systems that are virtualization hosts, >>providing remote services, or running locally confined processes. >> >>For "2", I think that the comparison to userspace ASLR entropy isn't >>as direct. For userspace, most systems don't tend to have any kind of >>watchdog on segfaulting processes, so a remote attacker could just >>keep trying an attack until they got lucky, in which case low entropy >>is a serious problem. In the case of KASLR, a single attack failure >>means the system goes down, which makes mounting an attack much more >>difficult. I think 8 bits is fine to start with, and I think start >>with a base offset ASLR is a good first step. We can improve things in >>the future. >> >>-Kees >> >>-- >>Kees Cook >>Chrome OS Security > > -- > Sent from my mobile phone. Please excuse brevity and lack of formatting. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/