Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755992AbdGXNRS (ORCPT ); Mon, 24 Jul 2017 09:17:18 -0400 Received: from mail-wm0-f49.google.com ([74.125.82.49]:35450 "EHLO mail-wm0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752881AbdGXNRJ (ORCPT ); Mon, 24 Jul 2017 09:17:09 -0400 Date: Mon, 24 Jul 2017 14:17:07 +0100 From: Matt Fleming To: Naoya Horiguchi Cc: Baoquan He , Kees Cook , linux-kernel@vger.kernel.org, x86@kernel.org, Thomas Gleixner , "H. Peter Anvin" , Ingo Molnar , izumi.taku@jp.fujitsu.com, Thomas Garnier , fanc.fnst@cn.fujitsu.com, "Jun'ichi Nomura" , Ard Biesheuvel Subject: Re: [PATCH v3 1/2] x86/boot/KASLR: exclude EFI_BOOT_SERVICES_{CODE|DATA} from KASLR's choice Message-ID: <20170724131707.GA11076@codeblueprint.co.uk> References: <20170710054733.GA22619@hori1.linux.bs1.fc.nec.co.jp> <1499665896-23731-1-git-send-email-n-horiguchi@ah.jp.nec.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1499665896-23731-1-git-send-email-n-horiguchi@ah.jp.nec.com> User-Agent: Mutt/1.5.24+42 (6e565710a064) (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1950 Lines: 48 On Mon, 10 Jul, at 02:51:35PM, Naoya Horiguchi wrote: > KASLR chooses kernel location from E820_TYPE_RAM regions by walking over > e820 entries now. E820_TYPE_RAM includes EFI_BOOT_SERVICES_CODE and > EFI_BOOT_SERVICES_DATA, so those regions can be the target. According to > UEFI spec, all memory regions marked as EfiBootServicesCode and > EfiBootServicesData are available for free memory after the first call > of ExitBootServices(). So such regions should be usable for kernel on > spec basis. > > In x86, however, we have some workaround for broken firmware, where we > keep such regions reserved until SetVirtualAddressMap() is done. > See the following code in should_map_region(): > > static bool should_map_region(efi_memory_desc_t *md) > { > ... > /* > * Map boot services regions as a workaround for buggy > * firmware that accesses them even when they shouldn't. > * > * See efi_{reserve,free}_boot_services(). > */ > if (md->type == EFI_BOOT_SERVICES_CODE || > md->type == EFI_BOOT_SERVICES_DATA) > return false; > > This workaround suppressed a boot crash, but potential issues still > remain because no one prevents the regions from overlapping with kernel > image by KASLR. > > So let's make sure that EFI_BOOT_SERVICES_{CODE|DATA} regions are never > chosen as kernel memory for the workaround to work fine. > > Signed-off-by: Naoya Horiguchi > --- > v2 -> v3: > - skip EFI_LOADER_CODE and EFI_LOADER_DATA in region scan > > v1 -> v2: > - switch efi_mirror_found to local variable > - insert break when EFI_MEMORY_MORE_RELIABLE found > --- > arch/x86/boot/compressed/kaslr.c | 44 +++++++++++++++++++++++++++++----------- > 1 file changed, 32 insertions(+), 12 deletions(-) I think the patch content is fine, but please update the comments and the changelog to say why EFI_CONVENTIONAL_MEMORY was chosen, i.e. that it's the only memory type that we know to be free.