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Message-ID: <20170725061711.GB18610@hori1.linux.bs1.fc.nec.co.jp>
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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