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

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Date:	Tue, 19 Nov 2013 14:20:11 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	akpm@...ux-foundation.org, mingo@...e.hu, hpa@...or.com,
	tglx@...utronix.de, 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


* Kirill A. Shutemov <kirill.shutemov@...ux.intel.com> wrote:

> Ingo Molnar wrote:
> > 
> > * 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.
> 
> What about this:
> 
> From 440f2cd4a7e6918b9238680e4eacd75dc30291b6 Mon Sep 17 00:00:00 2001
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> Date: Fri, 15 Nov 2013 14:14:05 -0800
> Subject: [PATCH] x86, mm: get ASLR works for hugetlb mappings
> 
> Matthew noticed that hugetlb doesn't participate in ASLR on x86-64.
> 
> %  for i in `seq 3`; do
> > tools/testing/selftests/vm/map_hugetlb | grep address
> > done
> Returned address is 0x2aaaaac00000
> Returned address is 0x2aaaaac00000
> Returned address is 0x2aaaaac00000
> 
> /proc/PID/maps entries for the mapping are always the same (except inode
> number):
> 
> 2aaaaac00000-2aaabac00000 rw-p 00000000 00:0c 8200                       /anon_hugepage (deleted)
> 2aaaaac00000-2aaabac00000 rw-p 00000000 00:0c 256                        /anon_hugepage (deleted)
> 2aaaaac00000-2aaabac00000 rw-p 00000000 00:0c 7180                       /anon_hugepage (deleted)
> 
> The reason is generic 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 switch hugetlb to use top-down unmapped area
> lookup.
> 
> %  for i in `seq 3`; do
> > tools/testing/selftests/vm/map_hugetlb | grep address
> > done
> Returned address is 0x7f4f08a00000
> Returned address is 0x7fdda4200000
> Returned address is 0x7febe0000000
> 
> /proc/PID/maps entries:
> 
> 7f4f08a00000-7f4f18a00000 rw-p 00000000 00:0c 1168                       /anon_hugepage (deleted)
> 7fdda4200000-7fddb4200000 rw-p 00000000 00:0c 7092                       /anon_hugepage (deleted)
> 7febe0000000-7febf0000000 rw-p 00000000 00:0c 7183                       /anon_hugepage (deleted)
>
> Unmapped area lookup policy for hugetlb mappings is consistent with
> normal mappings now -- the only difference is alignment requirements for
> huge pages.
> 
> libhugetlbfs test-suite didn't detect any regressions with the patch
> applied (although it shows few failures on my machine regardless the
> patch).

Perfect!

(I'll apply this to tip:x86/mm unless someone objects.)

Thanks,

	Ingo
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