linux-kernel - Re: [PATCH v5 3/4] arm64: mm: support ARCH_MMAP_RND

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Date:	Mon, 7 Dec 2015 10:26:16 +0000
From:	Jon Hunter <jonathanh@...dia.com>
To:	Daniel Cashman <dcashman@...roid.com>,
	<linux-kernel@...r.kernel.org>
CC:	<dcashman@...gle.com>, <linux-doc@...r.kernel.org>,
	<catalin.marinas@....com>, <will.deacon@....com>,
	<linux-mm@...ck.org>, <hpa@...or.com>, <mingo@...nel.org>,
	<aarcange@...hat.com>, <linux@....linux.org.uk>, <corbet@....net>,
	<xypron.glpk@....de>, <x86@...nel.org>, <hecmargi@....es>,
	<mgorman@...e.de>, <rientjes@...gle.com>, <bp@...e.de>,
	<nnk@...gle.com>, <dzickus@...hat.com>, <keescook@...omium.org>,
	<arnd@...db.de>, <jpoimboe@...hat.com>, <tglx@...utronix.de>,
	<n-horiguchi@...jp.nec.com>,
	<linux-arm-kernel@...ts.infradead.org>, <salyzyn@...roid.com>,
	<ebiederm@...ssion.com>, <jeffv@...gle.com>,
	<akpm@...ux-foundation.org>, <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v5 3/4] arm64: mm: support ARCH_MMAP_RND_BITS.


On 01/12/15 20:10, Daniel Cashman wrote:
> From: dcashman <dcashman@...gle.com>
> 
> arm64: arch_mmap_rnd() uses STACK_RND_MASK to generate the
> random offset for the mmap base address.  This value represents a
> compromise between increased ASLR effectiveness and avoiding
> address-space fragmentation. Replace it with a Kconfig option, which
> is sensibly bounded, so that platform developers may choose where to
> place this compromise. Keep default values as new minimums.
> 
> Signed-off-by: Daniel Cashman <dcashman@...roid.com>
> ---
>  arch/arm64/Kconfig   | 31 +++++++++++++++++++++++++++++++
>  arch/arm64/mm/mmap.c |  8 ++++++--
>  2 files changed, 37 insertions(+), 2 deletions(-)

[snip]

> diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
> index ed17747..af461b9 100644
> --- a/arch/arm64/mm/mmap.c
> +++ b/arch/arm64/mm/mmap.c
> @@ -51,8 +51,12 @@ unsigned long arch_mmap_rnd(void)
>  {
>  	unsigned long rnd;
>  
> -	rnd = (unsigned long)get_random_int() & STACK_RND_MASK;
> -
> +ifdef CONFIG_COMPAT
> +	if (test_thread_flag(TIF_32BIT))
> +		rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_compat_bits);
> +	else
> +#endif
> +		rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_bits);
>  	return rnd << PAGE_SHIFT;
>  }

The above is causing a build failure on -next today.

commit 42a6c8953112a9856dd09148c3d6a2cc106b6003
Author: Jon Hunter <jonathanh@...dia.com>
Date:   Mon Dec 7 10:15:47 2015 +0000

    ARM64: mm: Fix build failure caused by invalid ifdef statement
    
    Commit 2e4614190421 ("arm64-mm-support-arch_mmap_rnd_bits-v4") caused the
    following build failure due to a missing "#". Fix this.
    
    arch/arm64/mm/mmap.c: In function ‘arch_mmap_rnd’:
    arch/arm64/mm/mmap.c:54:1: error: ‘ifdef’ undeclared (first use in this function)
     ifdef CONFIG_COMPAT
      ^
    Signed-off-by: Jon Hunter <jonathanh@...dia.com>

diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index af461b935137..e59a75a308bc 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -51,7 +51,7 @@ unsigned long arch_mmap_rnd(void)
 {
        unsigned long rnd;
 
-ifdef CONFIG_COMPAT
+#ifdef CONFIG_COMPAT
        if (test_thread_flag(TIF_32BIT))
                rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_compat_bits);
        else

Cheers
Jon
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