Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756005AbdDMGwe (ORCPT ); Thu, 13 Apr 2017 02:52:34 -0400 Received: from mail-pg0-f51.google.com ([74.125.83.51]:34286 "EHLO mail-pg0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751159AbdDMGwb (ORCPT ); Thu, 13 Apr 2017 02:52:31 -0400 MIME-Version: 1.0 In-Reply-To: <87shlcq0es.fsf@skywalker.in.ibm.com> References: <1490730347-5165-1-git-send-email-bhsharma@redhat.com> <87shlcq0es.fsf@skywalker.in.ibm.com> From: Bhupesh Sharma Date: Thu, 13 Apr 2017 12:22:29 +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: 3095 Lines: 80 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 Regards, Bhupesh > >> +# CONSTANT = 16 for 64BIT and 8 for 32BIT >> +config ARCH_MMAP_RND_BITS_MIN >> + default 5 if PPC_256K_PAGES && 32BIT # 31 - 18 - 8 = 5 >> + default 7 if PPC_64K_PAGES && 32BIT # 31 - 16 - 8 = 7 >> + default 9 if PPC_16K_PAGES && 32BIT # 31 - 14 - 8 = 9 >> + default 11 if PPC_4K_PAGES && 32BIT # 31 - 12 - 8 = 11 >> + default 12 if PPC_256K_PAGES && 64BIT # 46 - 18 - 16 = 12 >> + default 14 if PPC_64K_PAGES && 64BIT # 46 - 16 - 16 = 14 >> + default 16 if PPC_16K_PAGES && 64BIT # 46 - 14 - 16 = 16 >> + default 18 if PPC_4K_PAGES && 64BIT # 46 - 12 - 16 = 18 >> + >> +# max bits determined by the following formula: > > > -aneesh >