linux-kernel - Re: [PATCH 1/5] arm: factor out mmap ASLR into mmap

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Message-ID: <20150309144831.GM8656@n2100.arm.linux.org.uk>
Date:	Mon, 9 Mar 2015 14:48:31 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Kees Cook <keescook@...omium.org>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux390@...ibm.com, x86@...nel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Oleg Nesterov <oleg@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	"David A. Long" <dave.long@...aro.org>,
	Andrey Ryabinin <a.ryabinin@...sung.com>,
	Arun Chandran <achandran@...sta.com>,
	Yann Droneaud <ydroneaud@...eya.com>,
	Min-Hua Chen <orca.chen@...il.com>,
	Paul Burton <paul.burton@...tec.com>,
	Alex Smith <alex@...x-smith.me.uk>,
	Markos Chandras <markos.chandras@...tec.com>,
	Jeff Bailey <jeffbailey@...gle.com>,
	Vineeth Vijayan <vvijayan@...sta.com>,
	Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	Hector Marco-Gisbert <hecmargi@....es>,
	Borislav Petkov <bp@...e.de>,
	Jan-Simon Möller <dl9pf@....de>,
	linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
	linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/5] arm: factor out mmap ASLR into mmap_rnd

On Mon, Mar 02, 2015 at 04:19:44PM -0800, Kees Cook wrote:
> In preparation for exporting per-arch mmap randomization functions,
> this moves the ASLR calculations for mmap on ARM into a separate routine.
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>

Looks fine, thanks.

Acked-by: Russell King <rmk+kernel@....linux.org.uk>

> ---
>  arch/arm/mm/mmap.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
> index 5e85ed371364..0f8bc158f2c6 100644
> --- a/arch/arm/mm/mmap.c
> +++ b/arch/arm/mm/mmap.c
> @@ -169,14 +169,21 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
>  	return addr;
>  }
>  
> -void arch_pick_mmap_layout(struct mm_struct *mm)
> +static unsigned long mmap_rnd(void)
>  {
> -	unsigned long random_factor = 0UL;
> +	unsigned long rnd = 0UL;
>  
>  	/* 8 bits of randomness in 20 address space bits */
>  	if ((current->flags & PF_RANDOMIZE) &&
>  	    !(current->personality & ADDR_NO_RANDOMIZE))
> -		random_factor = (get_random_int() % (1 << 8)) << PAGE_SHIFT;
> +		rnd = (get_random_int() % (1 << 8)) << PAGE_SHIFT;
> +
> +	return rnd;
> +}
> +
> +void arch_pick_mmap_layout(struct mm_struct *mm)
> +{
> +	unsigned long random_factor = mmap_rnd();
>  
>  	if (mmap_is_legacy()) {
>  		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
> -- 
> 1.9.1
> 

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