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Date:   Mon, 28 Jan 2019 10:20:55 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Rik van Riel <riel@surriel.com>,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        kernel-hardening@lists.openwall.com,
        Kees Cook <keescook@chromium.org>,
        Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH] mm: Prevent mapping slab pages to userspace
Message-Id: <20190128102055.5b0790549542891c4dca47a3@linux-foundation.org>
In-Reply-To: <20190125173827.2658-1-willy@infradead.org>
References: <20190125173827.2658-1-willy@infradead.org>
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On Fri, 25 Jan 2019 09:38:27 -0800 Matthew Wilcox <willy@infradead.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?