linux-kernel - Re: [PATCH] mm: Prevent mapping slab pages to userspace

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Message-ID: <CAGXu5jJkf4pKr0WVUcFitZnnUbq3annautZxzYPC0TQaB5HaGA@mail.gmail.com>
Date:   Tue, 29 Jan 2019 08:00:14 +1300
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Rik van Riel <riel@...riel.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH] mm: Prevent mapping slab pages to userspace

On Tue, Jan 29, 2019 at 7:21 AM Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> On Fri, 25 Jan 2019 09:38:27 -0800 Matthew Wilcox <willy@...radead.org> wrote:
>
> > It's never appropriate to map a page allocated by SLAB into userspace.
> > A buggy device driver might try this, or an attacker might be able to
> > find a way to make it happen.
>
> It wouldn't surprise me if someone somewhere is doing this.  Rather
> than mysteriously breaking their code, how about we emit a warning and
> still permit it to proceed, for a while?

It seems like a fatal condition to me? There's nothing to check that
such a page wouldn't get freed by the slab while still mapped to
userspace, right?

But I'll take warning over not checking. :)

-- 
Kees Cook