kernel-hardening - Re: [PATCH v2 21/29] ARM: kernel: use PC relative symbol references in suspend/resume code

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Message-ID: <CAKv+Gu9w6DH9o6-hBRzEKcsovd5TK_NzpygnugnrSMNFrkww+g@mail.gmail.com>
Date: Mon, 4 Sep 2017 20:17:40 +0100
From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
To: Nicolas Pitre <nicolas.pitre@...aro.org>
Cc: "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, 
	Kernel Hardening <kernel-hardening@...ts.openwall.com>, Arnd Bergmann <arnd@...db.de>, 
	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 v2 21/29] ARM: kernel: use PC relative symbol references
 in suspend/resume code

On 4 September 2017 at 19:24, Nicolas Pitre <nicolas.pitre@...aro.org> wrote:
> On Sun, 3 Sep 2017, Ard Biesheuvel wrote:
>
>> Replace some unnecessary absolute references with relative ones. Also,
>> to prepare for runtime relocation, which occurs with the caches on,
>> defer taking the absolute address of cpu_resume_after_mmu() until after
>> the MMU is enabled.
>>
>> Cc: Russell King <linux@...linux.org.uk>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>
> What's the point of that last hunk? I understand you load the address
> after the mMU is on. But you should be coming back from a sleep and
> caches ought to be clean at that point. Not that it is a bad thing to do
> but I don't understand your reason for it.
>

I simply attempted to eliminate all uses of relocated quantities with
the caches off, but you are correct that this is only necessary for
boot and not for suspend/resume. This is actually somewhat of a
relief, since there is so much SOC specific suspend/resume code under
arch/arm, and the boot code is mostly shared.

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