From mboxrd@z Thu Jan  1 00:00:00 1970
From: Michael Ellerman <mpe@ellerman.id.au>
In-Reply-To: <20170202122256.GD5179@localhost.localdomain>
References: <1486014168-1279-1-git-send-email-bhsharma@redhat.com> <1486014168-1279-2-git-send-email-bhsharma@redhat.com> <87mve4c2my.fsf@concordia.ellerman.id.au> <20170202122256.GD5179@localhost.localdomain>
Date: Fri, 03 Feb 2017 10:59:23 +1100
Message-ID: <87efzgb0v8.fsf@concordia.ellerman.id.au>
MIME-Version: 1.0
Content-Type: text/plain
Subject: Re: [kernel-hardening] Re: [PATCH 1/2] powerpc: mm: support ARCH_MMAP_RND_BITS
To: Balbir Singh <bsingharora@gmail.com>
Cc: Bhupesh Sharma <bhsharma@redhat.com>, linuxppc-dev@lists.ozlabs.org, kernel-hardening@lists.openwall.com, Anatolij Gustschin <agust@denx.de>, keescook@chromium.org, Daniel Cashman <dcashman@android.com>, Scott Wood <oss@buserror.net>, Paul Mackerras <paulus@samba.org>, dcashman@google.com, Alistair Popple <alistair@popple.id.au>, bhupesh.linux@gmail.com, Alexander Graf <agraf@suse.com>
List-ID: <kernel-hardening.lists.openwall.com>

Balbir Singh <bsingharora@gmail.com> writes:

> On Thu, Feb 02, 2017 at 09:23:33PM +1100, Michael Ellerman wrote:
>> +config ARCH_MMAP_RND_BITS_MIN
>> +	# On 64-bit up to 1G of address space (2^30)
>> +	default 12 if 64BIT && PPC_256K_PAGES 	# 256K (2^18), = 30 - 18 = 12
>> +	default 14 if 64BIT && PPC_64K_PAGES  	# 64K  (2^16), = 30 - 16 = 14
>> +	default 16 if 64BIT && PPC_16K_PAGES  	# 16K  (2^14), = 30 - 14 = 16
>> +	default 18 if 64BIT			# 4K   (2^12), = 30 - 12 = 18
>> +	default ARCH_MMAP_RND_COMPAT_BITS_MIN
>> +
>> +config ARCH_MMAP_RND_BITS_MAX
>> +	# On 64-bit up to 32T of address space (2^45)
>
> I thought it was 64T, TASK_SIZE_USER64 is 2^46?

The virtual address space is 64T. The comment is talking about how much
can be taking up by the randomisation factor.

cheers