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Subject: Re: [PATCH REBASE v4 05/14] arm64, mm: Make randomization selected by
 generic topdown mmap layout
To:     Luis Chamberlain <mcgrof@kernel.org>
Cc:     Albert Ou <aou@eecs.berkeley.edu>,
        Kees Cook <keescook@chromium.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Palmer Dabbelt <palmer@sifive.com>,
        Will Deacon <will.deacon@arm.com>,
        Russell King <linux@armlinux.org.uk>,
        Ralf Baechle <ralf@linux-mips.org>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Paul Burton <paul.burton@mips.com>,
        linux-riscv@lists.infradead.org,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        James Hogan <jhogan@kernel.org>, linux-fsdevel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-mips@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
        linux-arm-kernel@lists.infradead.org
References: <20190724055850.6232-1-alex@ghiti.fr>
 <20190724055850.6232-6-alex@ghiti.fr>
 <20190724171123.GV19023@42.do-not-panic.com>
From:   Alexandre Ghiti <alex@ghiti.fr>
Message-ID: <8dd7b018-7f17-0018-0fcf-d0257976d275@ghiti.fr>
Date:   Thu, 25 Jul 2019 07:48:44 +0200
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On 7/24/19 7:11 PM, Luis Chamberlain wrote:
> On Wed, Jul 24, 2019 at 01:58:41AM -0400, Alexandre Ghiti wrote:
>> diff --git a/mm/util.c b/mm/util.c
>> index 0781e5575cb3..16f1e56e2996 100644
>> --- a/mm/util.c
>> +++ b/mm/util.c
>> @@ -321,7 +321,15 @@ unsigned long randomize_stack_top(unsigned long stack_top)
>>   }
>>   
>>   #ifdef CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
>> -#ifdef CONFIG_ARCH_HAS_ELF_RANDOMIZE
>> +unsigned long arch_randomize_brk(struct mm_struct *mm)
>> +{
>> +	/* Is the current task 32bit ? */
>> +	if (!IS_ENABLED(CONFIG_64BIT) || is_compat_task())
>> +		return randomize_page(mm->brk, SZ_32M);
>> +
>> +	return randomize_page(mm->brk, SZ_1G);
>> +}
>> +
>>   unsigned long arch_mmap_rnd(void)
>>   {
>>   	unsigned long rnd;
>> @@ -335,7 +343,6 @@ unsigned long arch_mmap_rnd(void)
>>   
>>   	return rnd << PAGE_SHIFT;
>>   }
> So arch_randomize_brk is no longer ifdef'd around
> CONFIG_ARCH_HAS_ELF_RANDOMIZE either and yet the header
> still has it. Is that intentional?
>

Yes, CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT selects 
CONFIG_ARCH_HAS_ELF_RANDOMIZE, that's what's new about v4: the generic
functions proposed in this series come with elf randomization.


Alex


>    Luis
>
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