From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f181.google.com (mail-ig0-f181.google.com [209.85.213.181]) by kanga.kvack.org (Postfix) with ESMTP id 211AF6B0255 for ; Tue, 3 Nov 2015 14:19:46 -0500 (EST) Received: by igpw7 with SMTP id w7so87655609igp.0 for ; Tue, 03 Nov 2015 11:19:45 -0800 (PST) Received: from mail-io0-x233.google.com (mail-io0-x233.google.com. [2607:f8b0:4001:c06::233]) by mx.google.com with ESMTPS id 3si21798792ioo.57.2015.11.03.11.19.45 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 03 Nov 2015 11:19:45 -0800 (PST) Received: by iody8 with SMTP id y8so29606060iod.1 for ; Tue, 03 Nov 2015 11:19:45 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <1446574204-15567-2-git-send-email-dcashman@android.com> References: <1446574204-15567-1-git-send-email-dcashman@android.com> <1446574204-15567-2-git-send-email-dcashman@android.com> Date: Tue, 3 Nov 2015 11:19:44 -0800 Message-ID: Subject: Re: [PATCH v2 2/2] arm: mm: support ARCH_MMAP_RND_BITS. From: Kees Cook Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Daniel Cashman Cc: LKML , Russell King - ARM Linux , Andrew Morton , Ingo Molnar , "linux-arm-kernel@lists.infradead.org" , Jonathan Corbet , Don Zickus , "Eric W. Biederman" , Heinrich Schuchardt , jpoimboe@redhat.com, "Kirill A. Shutemov" , n-horiguchi@ah.jp.nec.com, Andrea Arcangeli , Mel Gorman , Thomas Gleixner , David Rientjes , Linux-MM , "linux-doc@vger.kernel.org" , Mark Salyzyn , Jeffrey Vander Stoep , Nick Kralevich , dcashman On Tue, Nov 3, 2015 at 10:10 AM, Daniel Cashman wrote: > From: dcashman > > arm: arch_mmap_rnd() uses a hard-code value of 8 to generate the > random offset for the mmap base address. This value represents a > compromise between increased ASLR effectiveness and avoiding > address-space fragmentation. Replace it with a Kconfig option, which > is sensibly bounded, so that platform developers may choose where to > place this compromise. Keep 8 as the minimum acceptable value. > > Signed-off-by: Daniel Cashman Acked-by: Kees Cook Russell, if you don't see any problems here, it might make sense not to put this through the ARM patch tracker since it depends on the 1/2, and I think x86 and arm64 (and possibly other arch) changes are coming too. > --- > Changes in v2: > - Changed arch/arm/Kconfig and arch/arm/mm/mmap.c to reflect changes > in [PATCH v2 1/2], specifically the movement of variables to global > rather than arch-specific files. > > arch/arm/Kconfig | 10 ++++++++++ > arch/arm/mm/mmap.c | 3 +-- > 2 files changed, 11 insertions(+), 2 deletions(-) > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig > index 639411f..47d7561 100644 > --- a/arch/arm/Kconfig > +++ b/arch/arm/Kconfig > @@ -35,6 +35,7 @@ config ARM > select HAVE_ARCH_BITREVERSE if (CPU_32v7M || CPU_32v7) && !CPU_32v6 > select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32 > select HAVE_ARCH_KGDB if !CPU_ENDIAN_BE32 > + select HAVE_ARCH_MMAP_RND_BITS > select HAVE_ARCH_SECCOMP_FILTER if (AEABI && !OABI_COMPAT) > select HAVE_ARCH_TRACEHOOK > select HAVE_BPF_JIT > @@ -306,6 +307,15 @@ config MMU > Select if you want MMU-based virtualised addressing space > support by paged memory management. If unsure, say 'Y'. > > +config ARCH_MMAP_RND_BITS_MIN > + default 8 > + > +config ARCH_MMAP_RND_BITS_MAX > + default 14 if MMU && PAGE_OFFSET=0x40000000 > + default 15 if MMU && PAGE_OFFSET=0x80000000 > + default 16 if MMU > + default 8 > + > # > # The "ARM system type" choice list is ordered alphabetically by option > # text. Please add new entries in the option alphabetic order. > diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c > index 407dc78..c938693 100644 > --- a/arch/arm/mm/mmap.c > +++ b/arch/arm/mm/mmap.c > @@ -173,8 +173,7 @@ unsigned long arch_mmap_rnd(void) > { > unsigned long rnd; > > - /* 8 bits of randomness in 20 address space bits */ > - rnd = (unsigned long)get_random_int() % (1 << 8); > + rnd = (unsigned long)get_random_int() % (1 << mmap_rnd_bits); > > return rnd << PAGE_SHIFT; > } I like this getting pulled closer and closer to having arch_mmap_rnd() be identical across all architectures, and then we can just pull it out and leave the true variable: the entropy size. Do you have patches for x86 and arm64? -Kees > -- > 2.6.0.rc2.230.g3dd15c0 > -- Kees Cook Chrome OS Security -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org