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

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Message-ID: <20190724171123.GV19023@42.do-not-panic.com>
Date:   Wed, 24 Jul 2019 17:11:23 +0000
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Alexandre Ghiti <alex@...ti.fr>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Kees Cook <keescook@...omium.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mips@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH REBASE v4 05/14] arm64, mm: Make randomization selected
 by generic topdown mmap layout

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?

  Luis