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Date: Fri, 7 Jul 2017 11:58:14 +0100
From: Matt Fleming <matt@...eblueprint.co.uk>
To: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc: Baoquan He <bhe@...hat.com>, Kees Cook <keescook@...omium.org>,
LKML <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] x86/boot/KASLR: exclude EFI_BOOT_SERVICES_{CODE|DATA}
from KASLR's choice
On Fri, 07 Jul, at 06:11:24AM, Naoya Horiguchi wrote:
> On Fri, Jul 07, 2017 at 11:07:59AM +0800, Baoquan He wrote:
> > On 07/06/17 at 03:57pm, Matt Fleming wrote:
> > > On Thu, 06 Jul, at 08:31:07AM, Naoya Horiguchi wrote:
> > > > + for (i = 0; i < nr_desc; i++) {
> > > > + md = (efi_memory_desc_t *)(pmap + (i * e->efi_memdesc_size));
> > > > +
> > > > + /*
> > > > + * EFI_BOOT_SERVICES_{CODE|DATA} are avoided because boot
> > > > + * services regions could be accessed after ExitBootServices()
> > > > + * due to the workaround for buggy firmware.
> > > > + */
> > > > + if (!(md->type == EFI_LOADER_CODE ||
> > > > + md->type == EFI_LOADER_DATA ||
> > > > + md->type == EFI_CONVENTIONAL_MEMORY))
> > > > + continue;
> > >
> > > Wouldn't it make more sense to *only* use EFI_CONVENTIONAL_MEMORY?
> > >
> > > You can't re-use EFI_LOADER_* regions because the kaslr code is run so
> > > early in boot that you've no idea if data the kernel will need is in
> > > those EFI_LOADER_* regions.
> > >
> > > For example, we pass struct setup_data objects inside of
> > > EFI_LOADER_DATA regions.
> >
> > It doesn't matter because we have tried to avoid those memory setup_data
> > resides in in mem_avoid_overlap(). Here discarding EFI_LOADER_* could
> > discard the whole regions while setup_data could occupy small part of
> > them.
>
> Hi Matt, Baoquan,
>
> I added these three checks to accept any regions corresponding to
> E820_TYPE_RAM except EFI_BOOT_SERVICES_*, just thinking of that it's minimum
> surprising. Baoquan gave a good justification on that, so I'll leave it
> as-is in next version.
I disagree. The least surprising option would be to use the region
type that everyone (boot loader, kernel, firmware) agrees is free:
EFI_CONVENTIONAL_MEMORY.
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