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

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Date:   Mon, 30 Mar 2020 10:38:50 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     Patricia Alfonso <trishalfonso@...gle.com>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        anton.ivanov@...bridgegreys.com,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        David Gow <davidgow@...gle.com>, linux-um@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>
Subject: Re: [PATCH] UML: add support for KASAN under x86_64

On Mon, Mar 30, 2020 at 9:44 AM Johannes Berg <johannes@...solutions.net> wrote:
>
> On Fri, 2020-03-20 at 16:18 +0100, Dmitry Vyukov wrote:
> >
> > > Wait ... Now you say 0x7fbfffc000, but that is almost fine? I think you
> > > confused the values - because I see, on userspace, the following:
> >
> > Oh, sorry, I copy-pasted wrong number. I meant 0x7fff8000.
>
> Right, ok.
>
> > Then I would expect 0x1000 0000 0000 to work, but you say it doesn't...
>
> So it just occurred to me - as I was mentioning this whole thing to
> Richard - that there's probably somewhere some check about whether some
> space is userspace or not.
>
> I'm beginning to think that we shouldn't just map this outside of the
> kernel memory system, but properly treat it as part of the memory that's
> inside. And also use KASAN_VMALLOC.
>
> We can probably still have it at 0x7fff8000, just need to make sure we
> actually map it? I tried with vm_area_add_early() but it didn't really
> work once you have vmalloc() stuff...

But we do mmap it, no? See kasan_init() -> kasan_map_memory() -> mmap.