Messages in this thread | | | Date | Mon, 28 Aug 2017 15:55:42 +0800 | From | Baoquan He <> | Subject | Re: [PATCH v5] x86/boot/KASLR: exclude EFI_BOOT_SERVICES_* and EFI_LOADER_* from KASLR's choice |
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On 08/28/17 at 07:44am, Naoya Horiguchi wrote: > From 93182d1d8c2ce11232f7686c01dc16ee96e062c4 Mon Sep 17 00:00:00 2001 > From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> > Date: Mon, 28 Aug 2017 16:30:59 +0900 > Subject: [PATCH v5] x86/boot/KASLR: exclude EFI_BOOT_SERVICES_* and EFI_LOADER_* > from KASLR's choice > > 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, > EFI_LOADER_{CODE|DATA} regions are also excluded because they can be > used after ExitBootServices() as defined in EFI spec. As a result, we > choose kernel address only from EFI_CONVENTIONAL_MEMORY which is the > only memory type we know to be free. > > Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Thanks, looks good to me. Ack it.
Acked-by: Baoquan He <bhe@redhat.com>
> --- > v4 -> v5: > - addressed why EFI_LOADER_* is excluded. > - changed patch subject. > > 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 a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c > index 7de23bb279ce..ba5e9e5aaa89 100644 > --- a/arch/x86/boot/compressed/kaslr.c > +++ b/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 > -- > 2.7.4 >
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