From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753655AbaIEWRT (ORCPT ); Fri, 5 Sep 2014 18:17:19 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54972 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751508AbaIEWRS (ORCPT ); Fri, 5 Sep 2014 18:17:18 -0400 Date: Sat, 6 Sep 2014 06:16:57 +0800 From: Baoquan He To: Kees Cook Cc: LKML , Andi Kleen , Ingo Molnar , Thomas Deutschmann , Dave Young , Thomas Gleixner , Vivek Goyal , WANG Chao Subject: Re: [PATCH 2/4] kaslr: check if the random addr is available Message-ID: <20140905221657.GA1675@dhcp-17-102.nay.redhat.com> References: <1409926097-2101-1-git-send-email-bhe@redhat.com> <1409926097-2101-3-git-send-email-bhe@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/05/14 at 10:16am, Kees Cook wrote: > On Fri, Sep 5, 2014 at 7:08 AM, Baoquan He wrote: > > diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c > > index 7780a5b..d2a0eaa 100644 > > --- a/arch/x86/boot/compressed/misc.c > > +++ b/arch/x86/boot/compressed/misc.c > > @@ -250,6 +250,11 @@ static void handle_relocations(void *output, unsigned long output_len) > > } > > #endif > > > > + if (max_addr > CONFIG_RANDOMIZE_BASE_MAX_OFFSET) { > > + debug_putstr("Random addr is not allowed. No relocation needed... \n"); > > + return; > > + } > > + > > It's not clear to me what this is fixing. In aslr.c, > process_e820_entry() should already make it impossible to select > max_addr > CONFIG_RANDOMIZE_BASE_MAX_OFFSET. If you're trying to > detect a non-kaslr boot, I think this is better handled in 1/4 where I > suggest examining the "output" location before/after > choose_kernel_location. > > -Kees Hi Kees, Yes, process_e820_entry() can make sure the choice+output_len < CONFIG_RANDOMIZE_BASE_MAX_OFFSET, but that can't stop other bootloaders to put kernel in region above CONFIG_RANDOMIZE_BASE_MAX_OFFSET. E.g in kdump, we can set crashkernel=256M@1024M in cmdline. Then the 1st kernel will reserve 256M memory just at 1024M place. So if load kdump kernel now, the output will be 1024M before choose_kernel_location(). With this value, output won't be changed in choose_kernel_location(), then it will do decompress(), then call handle_relocations(). Then since 1024 is not equal to LOAD_PHYSICAL_ADDR, it will start relocatoins handling. And this cause _text stamping into MODULES vaddr range. System will be exceptional. Thanks Baoquan > > > /* > > * Calculate the delta between where vmlinux was linked to load > > * and where it was actually loaded. > > -- > > 1.8.5.3 > > > > > > -- > Kees Cook > Chrome OS Security