Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752742AbdHXKeB (ORCPT ); Thu, 24 Aug 2017 06:34:01 -0400 Received: from mail-pg0-f65.google.com ([74.125.83.65]:35819 "EHLO mail-pg0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752172AbdHXKd7 (ORCPT ); Thu, 24 Aug 2017 06:33:59 -0400 From: Naoya Horiguchi To: Naoya Horiguchi Cc: Baoquan He , Kees Cook , linux-kernel@vger.kernel.org, , Thomas Gleixner , "H. Peter Anvin" , Ingo Molnar , , Thomas Garnier , , Matt Fleming , "Jun'ichi Nomura" , Ard Biesheuvel Subject: [PATCH v4] x86/boot/KASLR: exclude EFI_BOOT_SERVICES_{CODE|DATA} from KASLR's choice Date: Thu, 24 Aug 2017 19:33:51 +0900 Message-Id: <1503570831-9683-1-git-send-email-n-horiguchi@ah.jp.nec.com> X-Mailer: git-send-email 2.7.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3628 Lines: 105 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. Furthermore, we choose kernel address only from EFI_CONVENTIONAL_MEMORY because it's the only memory type we know to be free. Signed-off-by: Naoya Horiguchi --- v3 -> v4: - update comment and patch description to mention why only EFI_CONVENTIONAL_MEMORY is chosen. - use efi_early_memdesc_ptr() - I decided not to post cleanup patches (patch 2/2 in previous series) because it's not necessary to fix the issue. 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 | 35 ++++++++++++++++++++++++++--------- 1 file changed, 26 insertions(+), 9 deletions(-) diff --git tip/x86/boot/arch/x86/boot/compressed/kaslr.c tip/x86/boot_patched/arch/x86/boot/compressed/kaslr.c index 7de23bb..ba5e9e5 100644 --- tip/x86/boot/arch/x86/boot/compressed/kaslr.c +++ tip/x86/boot_patched/arch/x86/boot/compressed/kaslr.c @@ -597,19 +597,36 @@ process_efi_entries(unsigned long minimum, unsigned long image_size) for (i = 0; i < nr_desc; i++) { md = efi_early_memdesc_ptr(pmap, e->efi_memdesc_size, i); if (md->attribute & EFI_MEMORY_MORE_RELIABLE) { - region.start = md->phys_addr; - region.size = md->num_pages << EFI_PAGE_SHIFT; - process_mem_region(®ion, minimum, image_size); efi_mirror_found = true; - - if (slot_area_index == MAX_SLOT_AREA) { - debug_putstr("Aborted EFI scan (slot_areas full)!\n"); - break; - } + break; } } - return efi_mirror_found; + for (i = 0; i < nr_desc; i++) { + md = efi_early_memdesc_ptr(pmap, e->efi_memdesc_size, i); + + /* + * According to spec, EFI_BOOT_SERVICES_{CODE|DATA} are also + * available for kernel image, but we don't include them for + * the workaround for buggy firmware. + * Only EFI_CONVENTIONAL_MEMORY is guaranteed to be free. + */ + if (md->type != EFI_CONVENTIONAL_MEMORY) + continue; + + if (efi_mirror_found && + !(md->attribute & EFI_MEMORY_MORE_RELIABLE)) + continue; + + region.start = md->phys_addr; + region.size = md->num_pages << EFI_PAGE_SHIFT; + process_mem_region(®ion, minimum, image_size); + if (slot_area_index == MAX_SLOT_AREA) { + debug_putstr("Aborted EFI scan (slot_areas full)!\n"); + break; + } + } + return true; } #else static inline bool -- 2.7.0