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

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Message-ID: <010001689613c1b5-6539225d-b74e-4248-8d8f-5b801c1a333b-000000@email.amazonses.com>
Date:   Mon, 28 Jan 2019 20:08:23 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Kees Cook <keescook@...omium.org>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Rik van Riel <riel@...riel.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, 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.