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Date: Mon, 21 Aug 2017 11:39:15 +0100
From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
To: Mark Rutland <mark.rutland@....com>
Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>, 
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, Arnd Bergmann <arnd@...db.de>, 
	Nicolas Pitre <nico@...aro.org>, Russell King <linux@...linux.org.uk>, 
	Kees Cook <keescook@...omium.org>, Thomas Garnier <thgarnie@...gle.com>, 
	Marc Zyngier <marc.zyngier@....com>, Tony Lindgren <tony@...mide.com>, 
	Matt Fleming <matt@...eblueprint.co.uk>, Dave Martin <dave.martin@....com>
Subject: Re: [PATCH 29/30] efi/libstub: arm: reserve bootloader supplied
 initrd in memory map

On 21 August 2017 at 11:37, Mark Rutland <mark.rutland@....com> wrote:
> On Mon, Aug 14, 2017 at 01:54:10PM +0100, Ard Biesheuvel wrote:
>> Under KASLR, the EFI stub may allocate the kernel anywhere in the
>> physical address space, which could be right on top of an initrd
>> if it was supplied by the bootloader (i.e., GRUB) in /chosen rather
>> than passed via the initrd= command line option. So allocate the
>> pages explicitly, this ensures that the random memory allocation
>> routine will disregard the region.
>
> I'm a little confused. Shouldn't the bootloader have allocated that
> memory, leaving it reserved?
>
> If it hasn't, then that region could be allcoated by anything else at
> any time (e.g. by the code which loads the kernel, or some EFI timer
> callback), so that sounds like a bootloader bug that we can't fix.
>

Yeah, thinko on my part. Thanks for spotting that.

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