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Re: [PATCH v3 1/4] mm: mmap: Add new /proc tunable for mmap_base ASLR.

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On Wed, 18 Nov 2015 15:20:05 -0800 Daniel Cashman <dcashman@android.com> wrote:

> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1568,6 +1568,28 @@ static struct ctl_table vm_table[] = {
>  		.mode		= 0644,
>  		.proc_handler	= proc_doulongvec_minmax,
>  	},
> +#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
> +	{
> +		.procname	= "mmap_rnd_bits",
> +		.data		= &mmap_rnd_bits,
> +		.maxlen		= sizeof(mmap_rnd_bits),
> +		.mode		= 0644,

Is there any harm in permitting the attacker to read these values?

And is there any benefit in permitting non-attackers to read them?

> +		.proc_handler	= proc_dointvec_minmax,
> +		.extra1		= &mmap_rnd_bits_min,
> +		.extra2		= &mmap_rnd_bits_max,
> +	},
> +#endif
> +#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS
> +	{
> +		.procname	= "mmap_rnd_compat_bits",
> +		.data		= &mmap_rnd_compat_bits,
> +		.maxlen		= sizeof(mmap_rnd_compat_bits),
> +		.mode		= 0644,
> +		.proc_handler	= proc_dointvec_minmax,
> +		.extra1		= &mmap_rnd_compat_bits_min,
> +		.extra2		= &mmap_rnd_compat_bits_max,
> +	},
> +#endif
>
> ...
>
> +#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
> +int mmap_rnd_bits_min = CONFIG_ARCH_MMAP_RND_BITS_MIN;
> +int mmap_rnd_bits_max = CONFIG_ARCH_MMAP_RND_BITS_MAX;
> +int mmap_rnd_bits = CONFIG_ARCH_MMAP_RND_BITS;
> +#endif
> +#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS
> +int mmap_rnd_compat_bits_min = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MIN;
> +int mmap_rnd_compat_bits_max = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MAX;
> +int mmap_rnd_compat_bits = CONFIG_ARCH_MMAP_RND_COMPAT_BITS;

These could be __read_mostly.

If one believes in such things.  One effect of __read_mostly is to
clump the write-often stuff into the same cachelines and I've never
been convinced that one outweighs the other...

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Thread

[PATCH v3 0/4] Allow customizable random offset to mmap_base address. Daniel Cashman <dcashman@android.com> - 2015-11-19 00:30 +0100
  [PATCH v3 1/4] mm: mmap: Add new /proc tunable for mmap_base ASLR. Daniel Cashman <dcashman@android.com> - 2015-11-19 00:30 +0100
    Re: [PATCH v3 1/4] mm: mmap: Add new /proc tunable for mmap_base  ASLR. Daniel Cashman <dcashman@android.com> - 2015-11-19 01:20 +0100
    Re: [PATCH v3 1/4] mm: mmap: Add new /proc tunable for mmap_base  ASLR. Andrew Morton <akpm@linux-foundation.org> - 2015-11-25 01:50 +0100
      Re: [PATCH v3 1/4] mm: mmap: Add new /proc tunable for mmap_base ASLR. Kees Cook <keescook@chromium.org> - 2015-11-25 01:50 +0100
        Re: [PATCH v3 1/4] mm: mmap: Add new /proc tunable for mmap_base  ASLR. Daniel Cashman <dcashman@android.com> - 2015-11-25 20:20 +0100
    Re: [PATCH v3 1/4] mm: mmap: Add new /proc tunable for mmap_base  ASLR. Michael Ellerman <mpe@ellerman.id.au> - 2015-11-25 05:50 +0100
      Re: [PATCH v3 1/4] mm: mmap: Add new /proc tunable for mmap_base  ASLR. Daniel Cashman <dcashman@android.com> - 2015-11-25 20:40 +0100
  Re: [PATCH v3 0/4] Allow customizable random offset to mmap_base  address. Andrew Morton <akpm@linux-foundation.org> - 2015-11-25 01:40 +0100
    Re: [PATCH v3 0/4] Allow customizable random offset to mmap_base  address. Daniel Cashman <dcashman@android.com> - 2015-11-25 20:10 +0100
      Re: [PATCH v3 0/4] Allow customizable random offset to mmap_base  address. Martin Schwidefsky <schwidefsky@de.ibm.com> - 2015-11-26 16:20 +0100
    Re: [PATCH v3 0/4] Allow customizable random offset to mmap_base  address. Michael Ellerman <mpe@ellerman.id.au> - 2015-11-26 08:10 +0100

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