linux-kernel - Re: [PATCH] arm64/mm: Remove hack in mmap randomize layout

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Message-ID: <20141118114120.GJ18842@arm.com>
Date:	Tue, 18 Nov 2014 11:41:20 +0000
From:	Will Deacon <will.deacon@....com>
To:	Yann Droneaud <ydroneaud@...eya.com>
Cc:	Catalin Marinas <Catalin.Marinas@....com>,
	Arnd Bergmann <arnd@...db.de>, Nicolas Pitre <nico@...aro.org>,
	Tony Lindgren <tony@...mide.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Anton Blanchard <anton@...ba.org>,
	Dan McGee <dpmcgee@...il.com>, Olof Johansson <olof@...om.net>,
	"David S. Miller" <davem@...emloft.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64/mm: Remove hack in mmap randomize layout

On Mon, Nov 17, 2014 at 11:02:19PM +0000, Yann Droneaud wrote:
> Since commit 8a0a9bd4db63 ('random: make get_random_int() more
> random'), get_random_int() returns a random value for each call,
> so comment and hack introduced in mmap_rnd() as part of commit
> 1d18c47c735e ('arm64: MMU fault handling and page table management')
> are incorrects.
> 
> Commit 1d18c47c735e seems to use the same hack introduced by
> commit a5adc91a4b44 ('powerpc: Ensure random space between stack
> and mmaps'), latter copied in commit 5a0efea09f42 ('sparc64: Sharpen
> address space randomization calculations.').
> 
> But both architectures were cleaned up as part of commit
> fa8cbaaf5a68 ('powerpc+sparc64/mm: Remove hack in mmap randomize
> layout') as hack is no more needed since commit 8a0a9bd4db63.
> 
> So the present patch removes the comment and the hack around
> get_random_int() on AArch64's mmap_rnd().
> 
> Cc: Dan McGee <dpmcgee@...il.com>
> Cc: David S. Miller <davem@...emloft.net>
> Cc: Anton Blanchard <anton@...ba.org>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Fixes: 1d18c47c735e ('arm64: MMU fault handling and page table management')
> Signed-off-by: Yann Droneaud <ydroneaud@...eya.com>
> ---
>  arch/arm64/mm/mmap.c | 12 ++----------
>  1 file changed, 2 insertions(+), 10 deletions(-)

Thanks, this looks sensible:

  Acked-by: Will Deacon <will.deacon@....com>

Will
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