linux-kernel - Re: [PATCH 4/7] arm64: Use simpler API for random address requests

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Message-ID: <20160729134804.GJ16593@arm.com>
Date:	Fri, 29 Jul 2016 14:48:05 +0100
From:	Will Deacon <will.deacon@....com>
To:	Jason Cooper <jason@...edaemon.net>
Cc:	william.c.roberts@...el.com, Yann Droneaud <ydroneaud@...eya.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	kernel-hardening@...ts.openwall.com, linux@....linux.org.uk,
	akpm@...ux-foundation.org, keescook@...omium.org, tytso@....edu,
	arnd@...db.de, gregkh@...uxfoundation.org, catalin.marinas@....com,
	ralf@...ux-mips.org, benh@...nel.crashing.org, paulus@...ba.org,
	mpe@...erman.id.au, davem@...emloft.net, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org,
	viro@...iv.linux.org.uk, nnk@...gle.com, jeffv@...gle.com,
	dcashman@...roid.com
Subject: Re: [PATCH 4/7] arm64: Use simpler API for random address requests

On Thu, Jul 28, 2016 at 08:47:27PM +0000, Jason Cooper wrote:
> Currently, all callers to randomize_range() set the length to 0 and
> calculate end by adding a constant to the start address.  We can
> simplify the API to remove a bunch of needless checks and variables.
> 
> Use the new randomize_addr(start, range) call to set the requested
> address.
> 
> Signed-off-by: Jason Cooper <jason@...edaemon.net>
> ---
>  arch/arm64/kernel/process.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 6cd2612236dc..11bf454baf86 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -374,12 +374,8 @@ unsigned long arch_align_stack(unsigned long sp)
>  
>  unsigned long arch_randomize_brk(struct mm_struct *mm)
>  {
> -	unsigned long range_end = mm->brk;
> -
>  	if (is_compat_task())
> -		range_end += 0x02000000;
> +		return randomize_addr(mm->brk, 0x02000000);
>  	else
> -		range_end += 0x40000000;
> -
> -	return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
> +		return randomize_addr(mm->brk, 0x40000000);

Looks fine to me, once the core code has settled down:

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

Will