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

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Date:   Thu, 16 Jan 2020 10:23:04 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Johannes Berg <johannes@...solutions.net>
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, Jan 16, 2020 at 10:20 AM Johannes Berg
<johannes@...solutions.net> wrote:
>
> 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*.

Even better! If we can reliably put something before constructors, we
don't even need lazy init in constructors.

> > 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
>
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