From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753525AbcCWBmF (ORCPT ); Tue, 22 Mar 2016 21:42:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37746 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753236AbcCWBl4 (ORCPT ); Tue, 22 Mar 2016 21:41:56 -0400 Date: Wed, 23 Mar 2016 09:41:49 +0800 From: Baoquan He To: Kees Cook Cc: LKML , Yinghai Lu , "H. Peter Anvin" , Ingo Molnar , Borislav Petkov , Vivek Goyal , Andy Lutomirski , lasse.collin@tukaani.org, Andrew Morton , Dave Young Subject: Re: [PATCH v4 19/20] x86, kaslr: Allow random address to be below loaded address Message-ID: <20160323014149.GA4048@x1.redhat.com> References: <1458631937-14593-1-git-send-email-bhe@redhat.com> <1458631937-14593-20-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 03/22/16 at 12:54pm, Kees Cook wrote: > On Tue, Mar 22, 2016 at 12:32 AM, Baoquan He wrote: > > From: Yinghai Lu > > > > Now new randomized output can only be chosen from regions above loaded > > address. In this case, for bootloaders like kexec which always loads > > kernel near the end of ram, it doesn't do randomization at all. Or kernel > > is loaded in a very big starting address, we should not give up that area > > is loaded in a very large address, then the area below the large loaded > > address will be given up. This is not reasonable. > > > > With correct tracking in mem_avoid we can allow random output below > > loaded address. With this change, though kexec can get random ouput > > below its loaded address of kernel. > > > > Now we just pick 512M as min_addr. If kernel loaded address is bigger than > > 512M, E.g 8G. Then [512M, 8G) can be added into random output candidate area. > > > > Signed-off-by: Yinghai Lu > > --- > > arch/x86/boot/compressed/aslr.c | 10 ++++++++-- > > 1 file changed, 8 insertions(+), 2 deletions(-) > > > > diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c > > index ddfc3d0..d072ca7 100644 > > --- a/arch/x86/boot/compressed/aslr.c > > +++ b/arch/x86/boot/compressed/aslr.c > > @@ -446,7 +446,8 @@ void choose_kernel_location(unsigned char *input, > > unsigned long output_size, > > unsigned char **virt_offset) > > { > > - unsigned long random; > > + unsigned long random, min_addr; > > + > > *virt_offset = (unsigned char *)LOAD_PHYSICAL_ADDR; > > > > #ifdef CONFIG_HIBERNATION > > @@ -467,8 +468,13 @@ void choose_kernel_location(unsigned char *input, > > mem_avoid_init((unsigned long)input, input_size, > > (unsigned long)*output); > > > > + /* start from 512M */ > > + min_addr = (unsigned long)*output; > > + if (min_addr > (512UL<<20)) > > + min_addr = 512UL<<20; > > The goal is to find a minimum address? I'm not sure this comment makes > sense. Shouldn't this be: > > /* Lower minimum to 512M. */ > min_addr = min_t(unsigned long, *output, 512UL << 20); > > Or something like that? Yes, the goal is to lower minimum to 512M. It's better to change it to "Lower minimum to 512M" as you suggested. I will resend a new one with this update into this thread. Thanks a lot for your great suggestion for patch log, code change and patch rearranging, and also appreciate your encouragement and patience. Thanks Baoquan > > > + > > /* Walk e820 and find a random address. */ > > - random = find_random_phy_addr((unsigned long)*output, output_size); > > + random = find_random_phy_addr(min_addr, output_size); > > if (!random) > > debug_putstr("KASLR could not find suitable E820 region...\n"); > > else { > > -- > > 2.5.0 > > > > -Kees > > -- > Kees Cook > Chrome OS & Brillo Security