Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756538Ab3DOVlp (ORCPT ); Mon, 15 Apr 2013 17:41:45 -0400 Received: from mail-oa0-f43.google.com ([209.85.219.43]:39974 "EHLO mail-oa0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755989Ab3DOVlo (ORCPT ); Mon, 15 Apr 2013 17:41:44 -0400 MIME-Version: 1.0 In-Reply-To: <516C702C.2030209@zytor.com> References: <1365797627-20874-1-git-send-email-keescook@chromium.org> <1365797627-20874-7-git-send-email-keescook@chromium.org> <516A1D49.1050100@zytor.com> <516C702C.2030209@zytor.com> Date: Mon, 15 Apr 2013 14:41:43 -0700 X-Google-Sender-Auth: luoy0thLXODfuHgt49yKKkuBsQk Message-ID: Subject: Re: [PATCH 6/6] x86: kaslr: relocate base offset at boot From: Kees Cook To: "H. Peter Anvin" Cc: Eric Northup , Yinghai Lu , Linux Kernel Mailing List , "kernel-hardening@lists.openwall.com" , Thomas Gleixner , Ingo Molnar , "the arch/x86 maintainers" , Jarkko Sakkinen , Matthew Garrett , Matt Fleming , Dan Rosenberg , Julien Tinnes , 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: 1845 Lines: 48 On Mon, Apr 15, 2013 at 2:25 PM, H. Peter Anvin wrote: > On 04/15/2013 02:06 PM, Eric Northup wrote: >> On Sat, Apr 13, 2013 at 8:06 PM, H. Peter Anvin wrote: >>> On 04/13/2013 05:37 PM, Yinghai Lu wrote: >>>> >>>> so decompress code position is changed? >>>> >>>> You may push out bss and other data area of run-time kernel of limit >>>> that boot loader >>>> chose according to setup_header.init_size. >>>> aka that make those area overlap with ram hole or other area like >>>> boot command line or initrd.... >>>> >>> >>> Is there a strong reason to randomize the physical address on 64 bits >>> (and if so, shouldn't we do it right?) >> >> The reason to randomize the physical address is because of the kernel >> direct mapping range -- a predictable-to-attackers physical address >> implies a predictable-to-attackers virtual address. >> >> It had seemed to me like changing the virtual base of the direct >> mapping would be much more involved than physically relocating the >> kernel, but better suggestions would be most welcome :-) >> > > You seem to be missing something here... > > There are *two* mappings in 64-bit mode. Physically, if you're going to > randomize you might as well randomize over the entire range... except > not too far down (on either 32 or 64 bit mode)... in particular, you > don't want to drop below 16 MiB if you can avoid it. > > On 64 bits, there is no reason the virtual address has to be randomized > the same way. Aren't we bound by the negative 2GB addressing due to -mcmodel=kernel? -Kees -- Kees Cook Chrome OS Security -- 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/