kernel-hardening - Re: [PATCH v2 00/29] implement KASLR for ARM

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Message-ID: <20170905164547.GA5024@atomide.com>
Date: Tue, 5 Sep 2017 09:45:48 -0700
From: Tony Lindgren <tony@...mide.com>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: linux-arm-kernel@...ts.infradead.org,
	kernel-hardening@...ts.openwall.com, 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>,
	Mark Rutland <mark.rutland@....com>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Dave Martin <dave.martin@....com>
Subject: Re: [PATCH v2 00/29] implement KASLR for ARM

Hi,

* Ard Biesheuvel <ard.biesheuvel@...aro.org> [170903 05:08]:
> 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 collect some pseudo-entropy, and randomize
>   the physical offset of the decompressed kernel, taking placement of DTB,
>   initrd and reserved regions into account
> - changes to the UEFI stub code to choose the KASLR offset and communicate
>   it to the decompressor
> 
> To test these changes, boot a multi_v7_defconfig+CONFIG_RANDOMIZE_BASE=y

I gave a quick try using your arm-kaslr-v3 branch, hopefully that's
the right one.

The good news is that now omap3 boots with omap2plus_defconfig with
and without CONFIG_RANDOMIZE_BASE=y and I did not see any compiler
errors with my gcc 6.2.0 like earlier :)

I did see boot attempts fail with randomize enable where no output
was produced. It seems this is happening for me maybe 1 out of 5 boots.
Enabling DEBUG_LL did not show anything either.

Then loading modules with CONFIG_RANDOMIZE_BASE=y seems to fail with:

$ sudo modprobe rtc-twl
rtc_twl: disagrees about version of symbol module_layout
modprobe: ERROR: could not insert 'rtc_twl': Exec format error

Regards,

Tony

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