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

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Message-Id: <20190128102055.5b0790549542891c4dca47a3@linux-foundation.org>
Date:   Mon, 28 Jan 2019 10:20:55 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-mm@...ck.org, 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@...ts.openwall.com,
        Kees Cook <keescook@...omium.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH] mm: Prevent mapping slab pages to userspace

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?