linux-kernel - Re: [RFC PATCH] UML: add support for KASAN under x86

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Message-ID: <2092169e6dd1f8d15f1db4b3787cc9fe596097b7.camel@sipsolutions.net>
Date:   Thu, 16 Jan 2020 10:20:26 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Patricia Alfonso <trishalfonso@...gle.com>,
        Richard Weinberger <richard@....at>,
        Jeff Dike <jdike@...toit.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        linux-um@...ts.infradead.org, David Gow <davidgow@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        anton.ivanov@...bridgegreys.com
Subject: Re: [RFC PATCH] UML: add support for KASAN under x86_64

On Thu, 2020-01-16 at 10:18 +0100, Dmitry Vyukov wrote:
> 
> Looking at this problem and at the number of KASAN_SANITIZE := n in
> Makefiles (some of which are pretty sad, e.g. ignoring string.c,
> kstrtox.c, vsprintf.c -- that's where the bugs are!), I think we
> initialize KASAN too late. I think we need to do roughly what we do in
> user-space asan (because it is user-space asan!). Constructors run
> before main and it's really good, we need to initialize KASAN from
> these constructors. Or if that's not enough in all cases, also add own
> constructor/.preinit array entry to initialize as early as possible.

We even control the linker in this case, so we can put something into
the .preinit array *first*.

> All we need to do is to call mmap syscall, there is really no
> dependencies on anything kernel-related.

OK. I wasn't really familiar with those details.

> This should resolve the problem with constructors (after they
> initialize KASAN, they can proceed to do anything they need) and it
> should get rid of most KASAN_SANITIZE (in particular, all of
> lib/Makefile and kernel/Makefile) and should fix stack instrumentation
> (in case it does not work now). The only tiny bit we should not
> instrument is the path from constructor up to mmap call.

That'd be great :)

johannes