From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754081AbcDFVwr (ORCPT ); Wed, 6 Apr 2016 17:52:47 -0400 Received: from mail-wm0-f68.google.com ([74.125.82.68]:34677 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753363AbcDFVwp (ORCPT ); Wed, 6 Apr 2016 17:52:45 -0400 Date: Wed, 6 Apr 2016 23:52:40 +0200 From: Ingo Molnar To: Kees Cook Cc: Linus Torvalds , "Rafael J. Wysocki" , Pavel Machek , Ard Biesheuvel , Matt Redfearn , Yves-Alexis Perez , Emrah Demir , Jonathan Corbet , the arch/x86 maintainers , "Rafael J. Wysocki" , Len Brown , Borislav Petkov , Andy Lutomirski , "open list:DOCUMENTATION" , "linux-pm@vger.kernel.org" , Linux Kernel Mailing List , "kernel-hardening@lists.openwall.com" Subject: Re: [PATCH] Prefer kASLR over Hibernation Message-ID: <20160406215240.GA25339@gmail.com> References: <20160406194404.GA11150@www.outflux.net> <20160406201716.GA14241@amd> <20160406214835.GA23620@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160406214835.GA23620@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Ingo Molnar wrote: > > * Kees Cook wrote: > > > On Wed, Apr 6, 2016 at 1:56 PM, Linus Torvalds > > wrote: > > > On Wed, Apr 6, 2016 at 1:17 PM, Pavel Machek wrote: > > >> > > >> Why is kASLR incompatible with hibernation? We can hibernate have > > >> 4.3 kernel resume hibernation image of 4.2 kernel (on x86-64, and I > > >> have patches for x86). Resuming kernel with different randomization > > >> does not look that much different... > > > > > > Oh, I'd absolutely prefer to just allow kaslr together with > > > hibernation if it actually works. > > > > > > Could the people who piped up to say that they actually use > > > hibernation just try passing in the "kaslr" command line option on > > > their machine, and see if it works for them? We could just remove the > > > "no kaslr with hibername" code - or at least limit it to 32-bit for > > > now.. > > > > > > Because that would be lovely. > > > > This is where our original investigation of having them coexist ended: > > https://lkml.org/lkml/2014/6/15/180 > > > > To quote Rafael Wysocki: > > > We're jumping from the boot kernel into the image kernel. The virtual address > > > comes from the image kernel, but the boot kernel has to use it. The only way > > > we can ensure that we'll jump to the right place is to pass the physical address > > > in the header (otherwise we de facto assume that the virtual address of the > > > target page frame will be the same in both the boot and the image kernels). > > > > > > The missing piece is that the code in swsusp_arch_resume() sets up temporary > > > page tables to ensure that they won't be overwritten while copying the last > > > remaining image kernel pages to the right page frames (those page tables > > > have to be stored in page frames that are free from the kernel image perspective). > > > > > > But if the kernel address space is randomized, set_up_temporary_mappings() > > > really should duplicate the existing layout instead of creating a new one from > > > scratch. Otherwise, virtual addresses before set_up_temporary_mappings() may > > > be different from the ones after it. > > So as I suggested it in the previous mail, the right solution would be to pass in > the randomization seed via a new kasl_seed=xyz boot option, and thus have the same > addresses as prior hibernation. > > That should make hibernation work as-is, with very little effort. > > Two details I can think of: > > 1) the new option has to be hidden from /proc/cmdline, due to: > > triton:~/tip> ll /proc/cmdline > -r--r--r-- 1 root root 0 Apr 6 23:45 /proc/cmdline > > 2) > > another detail is that the new boot option has to be checked in > choose_kernel_location(), to make sure it's done at the right point during bootup. > That's a good place to remove it from the boot options string as well. ... and I missed the biggest complication: to solve the chicken and egg problem with software_resume() running very late during bootup, software_resume() should probably kexec() the original kernel image, this time with the kaslr seed set in the boot parameters. So it's two bootups... Thanks, Ingo