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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Mon, 30 Mar 2020 10:38:50 +0200
Message-ID: <CACT4Y+YhwJK+F7Y7NaNpAwwWR-yZMfNevNp_gcBoZ+uMJRgsSA@mail.gmail.com>
Subject: Re: [PATCH] UML: add support for KASAN under x86_64
To:     Johannes Berg <johannes@sipsolutions.net>
Cc:     Patricia Alfonso <trishalfonso@google.com>,
        Jeff Dike <jdike@addtoit.com>,
        Richard Weinberger <richard@nod.at>,
        anton.ivanov@cambridgegreys.com,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Brendan Higgins <brendanhiggins@google.com>,
        David Gow <davidgow@google.com>, linux-um@lists.infradead.org,
        LKML <linux-kernel@vger.kernel.org>,
        kasan-dev <kasan-dev@googlegroups.com>
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On Mon, Mar 30, 2020 at 9:44 AM Johannes Berg <johannes@sipsolutions.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.