linux-kernel - Re: [PATCH REBASE v4 05/14] arm64, mm: Make randomization selected by generic topdown mmap layout

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Date:   Thu, 25 Jul 2019 07:48:44 +0200
From:   Alexandre Ghiti <alex@...ti.fr>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     Albert Ou <aou@...s.berkeley.edu>,
        Kees Cook <keescook@...omium.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Will Deacon <will.deacon@....com>,
        Russell King <linux@...linux.org.uk>,
        Ralf Baechle <ralf@...ux-mips.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Paul Burton <paul.burton@...s.com>,
        linux-riscv@...ts.infradead.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        James Hogan <jhogan@...nel.org>, linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mips@...r.kernel.org, Christoph Hellwig <hch@....de>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH REBASE v4 05/14] arm64, mm: Make randomization selected by
 generic topdown mmap layout

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
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

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