linux-kernel - Re: [PATCH v2 1/2] mm: mmap: Add new /proc tunable for mmap

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Message-Id: <20151103160410.34bbebc805c17d2f41150a19@linux-foundation.org>
Date:	Tue, 3 Nov 2015 16:04:10 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Daniel Cashman <dcashman@...roid.com>
Cc:	linux-kernel@...r.kernel.org, linux@....linux.org.uk,
	keescook@...omium.org, mingo@...nel.org,
	linux-arm-kernel@...ts.infradead.org, corbet@....net,
	dzickus@...hat.com, ebiederm@...ssion.com, xypron.glpk@....de,
	jpoimboe@...hat.com, kirill.shutemov@...ux.intel.com,
	n-horiguchi@...jp.nec.com, aarcange@...hat.com, mgorman@...e.de,
	tglx@...utronix.de, rientjes@...gle.com, linux-mm@...ck.org,
	linux-doc@...r.kernel.org, salyzyn@...roid.com, jeffv@...gle.com,
	nnk@...gle.com, dcashman <dcashman@...gle.com>
Subject: Re: [PATCH v2 1/2] mm: mmap: Add new /proc tunable for mmap_base
 ASLR.

On Tue,  3 Nov 2015 10:10:03 -0800 Daniel Cashman <dcashman@...roid.com> wrote:

> ASLR currently only uses 8 bits to generate the random offset for the
> mmap base address on 32 bit architectures. This value was chosen to
> prevent a poorly chosen value from dividing the address space in such
> a way as to prevent large allocations. This may not be an issue on all
> platforms. Allow the specification of a minimum number of bits so that
> platforms desiring greater ASLR protection may determine where to place
> the trade-off.

Can we please include a very good description of the motivation for this
change?  What is inadequate about the current code, what value does the
enhancement have to our users, what real-world problems are being solved,
etc.

Because all we have at present is "greater ASLR protection", which doesn't
really tell anyone anything.
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