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Date: Tue, 29 Jan 2019 08:00:14 +1300
From: Kees Cook <>
To: Andrew Morton <>
Cc: Matthew Wilcox <>, Linux-MM <>, 
	LKML <>, Rik van Riel <>, 
	Christoph Lameter <>, Pekka Enberg <>, David Rientjes <>, 
	Joonsoo Kim <>, 
	Kernel Hardening <>, Michael Ellerman <>
Subject: Re: [PATCH] mm: Prevent mapping slab pages to userspace

On Tue, Jan 29, 2019 at 7:21 AM Andrew Morton <> wrote:
> On Fri, 25 Jan 2019 09:38:27 -0800 Matthew Wilcox <> 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

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