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Date: Tue, 25 Jul 2017 06:17:11 +0000 From: Naoya Horiguchi <n-horiguchi@...jp.nec.com> To: Matt Fleming <matt@...eblueprint.co.uk> CC: Baoquan He <bhe@...hat.com>, Kees Cook <keescook@...omium.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>, "izumi.taku@...fujitsu.com" <izumi.taku@...fujitsu.com>, Thomas Garnier <thgarnie@...gle.com>, "fanc.fnst@...fujitsu.com" <fanc.fnst@...fujitsu.com>, Junichi Nomura <j-nomura@...jp.nec.com>, Ard Biesheuvel <ard.biesheuvel@...aro.org> Subject: Re: [PATCH v3 1/2] x86/boot/KASLR: exclude EFI_BOOT_SERVICES_{CODE|DATA} from KASLR's choice On Mon, Jul 24, 2017 at 02:17:07PM +0100, Matt Fleming wrote: > 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 <n-horiguchi@...jp.nec.com> > > --- > > 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. OK, I'll update this.
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