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

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Date:	Tue, 22 Oct 2013 08:21:25 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
CC:	Nadia Yvette Chambers <nyc@...omorphy.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Matthew Wilcox <willy@...ux.intel.com>
Subject: Re: [PATCH] x86, mm: get ASLR work for hugetlb mappings

On 10/22/2013 06:52 AM, Kirill A. Shutemov wrote:
> 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.

I have to wonder if this was on purpose in order to keep the large and
small mappings separate.  We don't *have* to keep them separate this, of
course, but it makes me wonder.

> 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.

Shouldn't we fix the generic code instead of further specializing the
x86 stuff?

In any case, you probably also want to run this through: the
libhugetlbfs tests:

http://sourceforge.net/p/libhugetlbfs/code/ci/master/tree/tests/
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