linux-hardening - Re: [PATCH v5] mm: Optional full ASLR for mmap(), mremap(), vdso and stack

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Message-ID: <alpine.DEB.2.22.394.2012031918220.193081@digraph.polyomino.org.uk>
Date:   Thu, 3 Dec 2020 19:26:25 +0000
From:   Joseph Myers <joseph@...esourcery.com>
To:     Florian Weimer <fweimer@...hat.com>
CC:     Andy Lutomirski <luto@...capital.net>,
        Topi Miettinen <toiwoton@...il.com>,
        <linux-hardening@...r.kernel.org>, <akpm@...ux-foundation.org>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        Mike Rapoport <rppt@...nel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH v5] mm: Optional full ASLR for mmap(), mremap(), vdso
 and stack

On Thu, 3 Dec 2020, Florian Weimer wrote:

> My knowledge of probability theory is quite limited, so I have to rely
> on simulations.  But I think you would see a 40 GiB gap somewhere for a
> 47-bit address space with 32K allocations, most of the time.  Which is
> not too bad.

This is very close to a Poisson process (if the number of small 
allocations being distributed independently in the address space is 
large), so the probability that any given gap is at least x times the mean 
gap is about exp(-x).

-- 
Joseph S. Myers
joseph@...esourcery.com