linux-kernel - Re: [PATCH 2/2] arm: apply more __ro_after

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Date:	Thu, 11 Aug 2016 00:02:42 +0100
From:	Russell King - ARM Linux <linux@...linux.org.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
	Kees Cook <keescook@...omium.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mathias Krause <minipli@...glemail.com>
Subject: Re: [PATCH 2/2] arm: apply more __ro_after_init

On Wed, Aug 10, 2016 at 09:31:05PM +0200, Arnd Bergmann wrote:
> On Wednesday, August 10, 2016 11:12:53 AM CEST Russell King - ARM Linux wrote:
> > There's the TLS emulation too, but that writes via the vectors mapping
> > at 0xffff0ff0.
> 
> Ok, so that should be safe. Can we change the fiq code to also use the
> high mapping and then take the __ro_after_init patch on top?

We can't - if the kernel is configured without the kuser helpers in
the vectors page, it's mapped read-only.  I'm not sure what the
intersection is between platforms that can have FIQs and platforms
that can disable the kuser helpers.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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