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Date: Wed, 28 Feb 2018 10:33:49 -0800
From: Matthew Wilcox <>
To: Ilya Smith <>
Cc: Kees Cook <>,
	Andrew Morton <>,
	Dan Williams <>,
	Michal Hocko <>,
	"Kirill A. Shutemov" <>,
	Jan Kara <>, Jerome Glisse <>,
	Hugh Dickins <>, Helge Deller <>,
	Andrea Arcangeli <>,
	Oleg Nesterov <>, Linux-MM <>,
	LKML <>,
	Kernel Hardening <>
Subject: Re: [RFC PATCH] Randomization of address chosen by mmap.

On Wed, Feb 28, 2018 at 08:13:00PM +0300, Ilya Smith wrote:
> > It would be worth spelling out the "not recommended" bit some more
> > too: this fragments the mmap space, which has some serious issues on
> > smaller address spaces if you get into a situation where you cannot
> > allocate a hole large enough between the other allocations.
> > 
> I’m agree, that's the point.

Would it be worth randomising the address returned just ever so slightly?
ie instead of allocating exactly the next address, put in a guard hole
of (configurable, by default maybe) 1-15 pages?  Is that enough extra
entropy to foil an interesting number of attacks, or do we need the full
randomise-the-address-space approach in order to be useful?

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