linux-kernel - Re: [patch 3/3] x86, mm: get ASLR work for hugetlb mappings

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Message-ID: <20131119083053.GB1243@gmail.com>
Date:	Tue, 19 Nov 2013 09:30:53 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	akpm@...ux-foundation.org
Cc:	mingo@...e.hu, hpa@...or.com, tglx@...utronix.de,
	kirill.shutemov@...ux.intel.com, dave.hansen@...el.com,
	mingo@...hat.com, n-horiguchi@...jp.nec.com, willy@...ux.intel.com,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 3/3] x86, mm: get ASLR work for hugetlb mappings


* akpm@...ux-foundation.org <akpm@...ux-foundation.org> wrote:

> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> Subject: x86, mm: get ASLR work for hugetlb mappings
> 
> Matthew noticed that hugetlb doesn't participate in ASLR on x86-64.  The
> reason is genereic hugetlb_get_unmapped_area() which is used on x86-64. 
> It doesn't support randomization and use bottom-up unmapped area lookup,
> instead of usual top-down on x86-64.
> 
> x86 has arch-specific hugetlb_get_unmapped_area(), but it's used only on
> x86-32.
> 
> Let's use arch-specific hugetlb_get_unmapped_area() on x86-64 too.  It
> fixes the issue and make hugetlb use top-down unmapped area lookup.

So the title and the changelog has typos (I counted three), which 
makes me wonder how well this was tested.

To show/document the testing effort a before/after /proc/PID/maps 
output showing hugetlb vma addresses would be nice, showing that ASLR 
didn't work before and that it works adequately after the patch.

A word about the range and granularity of randomization in the typical 
case would be nice as well.

Thanks,

	Ingo
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