kernel-hardening - Re: [PATCH 02/30] ARM: assembler: introduce adr_l, ldr_l and str

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Date: Mon, 14 Aug 2017 17:56:13 +0100
From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
To: Russell King - ARM Linux <linux@...linux.org.uk>
Cc: Nicolas Pitre <nicolas.pitre@...aro.org>, Dave Martin <Dave.Martin@....com>, 
	Mark Rutland <mark.rutland@....com>, Kees Cook <keescook@...omium.org>, 
	Arnd Bergmann <arnd@...db.de>, Marc Zyngier <marc.zyngier@....com>, 
	Kernel Hardening <kernel-hardening@...ts.openwall.com>, Tony Lindgren <tony@...mide.com>, 
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, Thomas Garnier <thgarnie@...gle.com>, 
	Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH 02/30] ARM: assembler: introduce adr_l, ldr_l and str_l macros

On 14 August 2017 at 17:42, Russell King - ARM Linux
<linux@...linux.org.uk> wrote:
> On Mon, Aug 14, 2017 at 05:22:39PM +0100, Ard Biesheuvel wrote:
>> On 14 August 2017 at 17:18, Nicolas Pitre <nicolas.pitre@...aro.org> wrote:
>> > On Mon, 14 Aug 2017, Dave Martin wrote:
>> >
>> >> On Mon, Aug 14, 2017 at 04:38:02PM +0100, Ard Biesheuvel wrote:
>> >> > That's a trick, actually, which I failed to add a comment for.
>> >
>> > Shame shame shame !
>> >
>> >> > We use .arm sections in the thumb2 kernel, and using these macros
>> >> > there would result in the wrong offset to be used. Adding the .w
>> >> > suffix forces an error in the assembler which even results in a fairly
>> >> > meaningful error message complaining about using .w in ARM code.
>> >>
>> >> Ewww... I think it'd be best to add a comment explaining that.
>> >
>> > Absolutely!
>> >
>>
>> Yeah, mea culpa.
>>
>> But if people have better ideas how to avoid this situation, I am all ears.
>
> Have you tested building an ARMv7M kernel with your patches - ARMv7M is
> Thumb only, so can't contain any ARM code.  If not, please try
> mps2_defconfig.
>

mps2_defconfig builds without error with these patches. I don't have
the hardware so I can't boot it, unfortunately.

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