Re: [RFC PATCH] UML: add support for KASAN under x86_64

From: Dmitry Vyukov <dvyukov@google.com>
To: Johannes Berg <johannes@sipsolutions.net>
Cc: Patricia Alfonso <trishalfonso@google.com>,
	Richard Weinberger <richard@nod.at>,
	Jeff Dike <jdike@addtoit.com>,
	Brendan Higgins <brendanhiggins@google.com>,
	LKML <linux-kernel@vger.kernel.org>,
	kasan-dev <kasan-dev@googlegroups.com>,
	linux-um@lists.infradead.org, David Gow <davidgow@google.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	anton.ivanov@cambridgegreys.com
Subject: Re: [RFC PATCH] UML: add support for KASAN under x86_64
Date: Thu, 16 Jan 2020 10:23:04 +0100	[thread overview]
Message-ID: <CACT4Y+b6C+y9sDfMYPDy-nh=WTt5+u2kLcWx2LQmHc1A5L7y0A@mail.gmail.com> (raw)
In-Reply-To: <2092169e6dd1f8d15f1db4b3787cc9fe596097b7.camel@sipsolutions.net>

On Thu, Jan 16, 2020 at 10:20 AM Johannes Berg
<johannes@sipsolutions.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
>
> --
> You received this message because you are subscribed to the Google Groups "kasan-dev" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to kasan-dev+unsubscribe@googlegroups.com.
> To view this discussion on the web visit https://groups.google.com/d/msgid/kasan-dev/2092169e6dd1f8d15f1db4b3787cc9fe596097b7.camel%40sipsolutions.net.