Date: Mon, 24 Aug 2015 18:47:36 +0100
From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Linus Walleij <linus.walleij@linaro.org>, Arnd Bergmann <arnd@arndb.de>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        David Keitel <dkeitel@codeaurora.org>,
        Alexander Potapenko <glider@google.com>,
        "linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dmitry Vyukov <dvyukov@google.com>
Subject: Re: [PATCH v2 5/5] arm64: add KASan support
Message-ID: <20150824174736.GD7557@n2100.arm.linux.org.uk>
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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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