Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756353AbdDMHqv (ORCPT ); Thu, 13 Apr 2017 03:46:51 -0400 Received: from mail-pg0-f53.google.com ([74.125.83.53]:34577 "EHLO mail-pg0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756160AbdDMHqs (ORCPT ); Thu, 13 Apr 2017 03:46:48 -0400 MIME-Version: 1.0 In-Reply-To: <03284709-498c-1e52-40f0-b19d20e56b8e@linux.vnet.ibm.com> References: <1490730347-5165-1-git-send-email-bhsharma@redhat.com> <87shlcq0es.fsf@skywalker.in.ibm.com> <03284709-498c-1e52-40f0-b19d20e56b8e@linux.vnet.ibm.com> From: Bhupesh Sharma Date: Thu, 13 Apr 2017 13:16:47 +0530 Message-ID: Subject: Re: [PATCH v3] powerpc: mm: support ARCH_MMAP_RND_BITS To: "Aneesh Kumar K.V" Cc: linuxppc-dev@lists.ozlabs.org, kernel-hardening@lists.openwall.com, linux-kernel@vger.kernel.org, Alistair Popple , Anatolij Gustschin , Kees Cook , Daniel Cashman , Scott Wood , Paul Mackerras , Daniel Cashman , Bhupesh SHARMA , Alexander Graf Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2898 Lines: 83 On Thu, Apr 13, 2017 at 12:28 PM, Aneesh Kumar K.V wrote: > > > On Thursday 13 April 2017 12:22 PM, Bhupesh Sharma wrote: >> >> Hi Aneesh, >> >> On Thu, Apr 13, 2017 at 12:06 PM, Aneesh Kumar K.V >> wrote: >>> >>> Bhupesh Sharma writes: >>> >>>> powerpc arch_mmap_rnd() currently uses hard-coded values - >>>> (23-PAGE_SHIFT) for >>>> 32-bit and (30-PAGE_SHIFT) for 64-bit, to generate the random offset >>>> for the mmap base address for a ASLR ELF. >>>> >>>> This patch makes sure that powerpc mmap arch_mmap_rnd() implementation >>>> is similar to other ARCHs (like x86, arm64) and uses mmap_rnd_bits >>>> and helpers to generate the mmap address randomization. >>>> >>>> The maximum and minimum randomization range values represent >>>> a compromise between increased ASLR effectiveness and avoiding >>>> address-space fragmentation. >>>> >>>> Using the Kconfig option and suitable /proc tunable, platform >>>> developers may choose where to place this compromise. >>>> >>>> Also this patch keeps the default values as new minimums. >>>> >>>> Signed-off-by: Bhupesh Sharma >>>> Reviewed-by: Kees Cook >>>> --- >>>> * Changes since v2: >>>> v2 can be seen here (https://patchwork.kernel.org/patch/9551509/) >>>> - Changed a few minimum and maximum randomization ranges as per >>>> Michael's suggestion. >>>> - Corrected Kees's email address in the Reviewed-by line. >>>> - Added further comments in kconfig to explain how the address >>>> ranges were worked out. >>>> >>>> * Changes since v1: >>>> v1 can be seen here >>>> (https://lists.ozlabs.org/pipermail/linuxppc-dev/2017-February/153594.html) >>>> - No functional change in this patch. >>>> - Dropped PATCH 2/2 from v1 as recommended by Kees Cook. >>>> >>>> arch/powerpc/Kconfig | 44 >>>> ++++++++++++++++++++++++++++++++++++++++++++ >>>> arch/powerpc/mm/mmap.c | 7 ++++--- >>>> 2 files changed, 48 insertions(+), 3 deletions(-) >>>> >>>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig >>>> index 97a8bc8..84aae67 100644 >>>> --- a/arch/powerpc/Kconfig >>>> +++ b/arch/powerpc/Kconfig >>>> @@ -22,6 +22,48 @@ config MMU >>>> bool >>>> default y >>>> >>>> +# min bits determined by the following formula: >>>> +# VA_BITS - PAGE_SHIFT - CONSTANT >>>> +# where, >>>> +# VA_BITS = 46 bits for 64BIT and 4GB - 1 Page = 31 bits for 32BIT >>> >>> >>> >>> Where did we derive that 46 bits from ? is that based on TASK_SIZE ? >> >> >> Yes. It was derived from TASK_SIZE : >> >> http://lxr.free-electrons.com/source/arch/powerpc/include/asm/processor.h#L105 >> > > That is getting update to 128TB by default and conditionally to 512TB Can't find the relevant patch in linus's master branch. Please share the appropriate patch/discussion link. Regards, Bhupesh