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Message-ID: <CAK8P3a1zJPsHphvoOitQbTaY-7rzFndGKatM2=aeUphkG+3T_A@mail.gmail.com>
Date: Mon, 14 Aug 2017 17:30:55 +0200
From: Arnd Bergmann <arnd@...db.de>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>, 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>,
Mark Rutland <mark.rutland@....com>, Tony Lindgren <tony@...mide.com>,
Matt Fleming <matt@...eblueprint.co.uk>, Dave Martin <dave.martin@....com>
Subject: Re: [PATCH 00/30] implement KASLR for ARM
On Mon, Aug 14, 2017 at 2:53 PM, Ard Biesheuvel
<ard.biesheuvel@...aro.org> wrote:
> This series implements randomization of the placement of the core ARM kernel
> inside the lowmem region. It consists of the following parts:
>
> - changes that allow us to build vmlinux as a PIE executable which retains
> the metadata required to fix up all absolute symbol references at runtime
> - changes that eliminate absolute references from low-level code that may
> execute with the MMU off: this removes the need to perform explicit cache
> maintenance after the absolute references have been fixed up at runtime with
> the caches enabled
> - changes to the core kernel startup code to take the physical offset into
> account when creating the virtual mapping (the pa-to-va mapping remains
> unchanged)
> - changes to the decompressor to take the KASLR offset into account when
> placing the kernel in physical memory
> - changes to the UEFI stub code to choose the KASLR offset and communicate
> it to the decompressor
Would it make sense to also randomize the pa-to-va mapping on top of this?
That can certainly be a later follow-up, I'm just trying to think of the options
we have, given that the kernel is now relocatable and we can support arbitrary
pa-to-va mappings already.
Can you explain how the random seed is passed from the bootloader
to the kernel when we don't use EFI? Is this implemented at all? I see
that you add a seed to "/chosen/kaslr-seed" in the EFI stub when using
the EFI boot services, but I don't see where that value gets read again
when we relocate the kernel.
Arnd
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