Re: [PATCH v2 1/2] mm: mmap: Add new /proc tunable for mmap_base ASLR.

From: Andrew Morton
Date: Tue Nov 03 2015 - 19:04:16 EST

On Tue, 3 Nov 2015 10:10:03 -0800 Daniel Cashman <dcashman@xxxxxxxxxxx> 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,

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