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Message-Id: <3w9nt9601Wz9s2P@ozlabs.org>
Date: Sun, 23 Apr 2017 21:53:21 +1000 (AEST)
From: Michael Ellerman <patch-notifications@...erman.id.au>
To: Michael Ellerman <mpe@...erman.id.au>, linuxppc-dev@...abs.org
Cc: bhsharma@...hat.com, keescook@...omium.org, kernel-hardening@...ts.openwall.com
Subject: Re: [v2] powerpc/mm: Add support for runtime configuration of ASLR limits
On Thu, 2017-04-20 at 14:36:20 UTC, Michael Ellerman wrote:
> Add powerpc support for mmap_rnd_bits and mmap_rnd_compat_bits, which are two
> sysctls that allow a user to configure the number of bits of randomness used for
> ASLR.
>
> Because of the way the Kconfig for ARCH_MMAP_RND_BITS is defined, we have to
> construct at least the MIN value in Kconfig, vs in a header which would be more
> natural. Given that we just go ahead and do it all in Kconfig.
>
> At least according to the code (the documentation makes no mention of it), the
> value is defined as the number of bits of randomisation *of the page*, not the
> address. This makes some sense, with larger page sizes more of the low bits are
> forced to zero, which would reduce the randomisation if we didn't take the
> PAGE_SIZE into account. However it does mean the min/max values have to change
> depending on the PAGE_SIZE in order to actually limit the amount of address
> space consumed by the randomisation.
>
> The result of that is that we have to define the default values based on both
> 32-bit vs 64-bit, but also the configured PAGE_SIZE. Furthermore now that we
> have 128TB address space support on Book3S, we also have to take that into
> account.
>
> Finally we can wire up the value in arch_mmap_rnd().
>
> Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
> Signed-off-by: Bhupesh Sharma <bhsharma@...hat.com>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
Applied to powerpc next.
https://git.kernel.org/powerpc/c/9fea59bd7ca541e5d0851f0b6dbca8
cheers
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