From mboxrd@z Thu Jan 1 00:00:00 1970 From: linux@armlinux.org.uk (Russell King - ARM Linux) Date: Thu, 11 Aug 2016 00:06:45 +0100 Subject: [PATCH 2/2] arm: apply more __ro_after_init In-Reply-To: <2760702.46Rp2Juk5b@wuerfel> References: <1464979224-2085-1-git-send-email-keescook@chromium.org> <20160810094339.GK1041@n2100.armlinux.org.uk> <2760702.46Rp2Juk5b@wuerfel> Message-ID: <20160810230645.GP1041@n2100.armlinux.org.uk> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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.