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Message-ID: <20160810230645.GP1041@n2100.armlinux.org.uk>
Date: Thu, 11 Aug 2016 00:06:45 +0100
From: Russell King - ARM Linux <linux@...linux.org.uk>
To: Arnd Bergmann <arnd@...db.de>
Cc: linux-arm-kernel@...ts.infradead.org, Kees Cook <keescook@...omium.org>,
linux-arch <linux-arch@...r.kernel.org>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
"x86@...nel.org" <x86@...nel.org>,
LKML <linux-kernel@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <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 09:41:23PM +0200, Arnd Bergmann wrote:
> It might be better to start by making the fixed mapping readonly,
> as KASLR doesn't protect that one at all, and change the TLS
> code accordingly.
I think that's impossible, because we gave userspace permission to
read 0xffff0ff0 directly without using __kuser_get_tls. You're
talking about potentially breaking userspace.
If you disable kuser helpers, then the page becomes read-only and
invisible to userspace anyway. So, everything is being done there
which can be done - if you have kuser helpers enabled, then you
lose some opportunities for these security improvements.
--
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.
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