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Date:   Mon, 28 Jan 2019 20:08:23 +0000
From:   Christopher Lameter <cl@linux.com>
To:     Kees Cook <keescook@chromium.org>
cc:     Andrew Morton <akpm@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>,
        Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Rik van Riel <riel@surriel.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH] mm: Prevent mapping slab pages to userspace
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On Tue, 29 Jan 2019, Kees Cook wrote:

> 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?

Lets just fail the code.  Currently this may work with SLUB. But SLAB and
SLOB overlay fields with mapcount. So you would have a corrupted page
struct if you mapped a slab page to user space.