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Message-ID: <20150824174736.GD7557@n2100.arm.linux.org.uk>
Date: Mon, 24 Aug 2015 18:47:36 +0100
From: Russell King - ARM Linux <linux@....linux.org.uk>
To: Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc: Linus Walleij <linus.walleij@...aro.org>,
Arnd Bergmann <arnd@...db.de>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
David Keitel <dkeitel@...eaurora.org>,
Alexander Potapenko <glider@...gle.com>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v2 5/5] arm64: add KASan support
On Mon, Aug 24, 2015 at 05:15:22PM +0300, Andrey Ryabinin wrote:
> Yes, ~130Mb (3G/1G split) should work. 512Mb shadow is optional.
> The only advantage of 512Mb shadow is better handling of user memory
> accesses bugs
> (access to user memory without copy_from_user/copy_to_user/strlen_user etc API).
No need for that to be handed by KASan. I have patches in linux-next,
now acked by Will, which prevent the kernel accessing userspace with
zero memory footprint. No need for remapping, we have a way to quickly
turn off access to userspace mapped pages on non-LPAE 32-bit CPUs.
(LPAE is not supported yet - Catalin will be working on that using the
hooks I'm providing once he returns.)
This isn't a debugging thing, it's a security hardening thing. Some
use-after-free bugs are potentially exploitable from userspace. See
the recent blackhat conference paper.
--
FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
according to speedtest.net.
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