Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757328AbbKRXSM (ORCPT ); Wed, 18 Nov 2015 18:18:12 -0500 Received: from mail-io0-f173.google.com ([209.85.223.173]:35895 "EHLO mail-io0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757002AbbKRXSJ (ORCPT ); Wed, 18 Nov 2015 18:18:09 -0500 MIME-Version: 1.0 In-Reply-To: <1447886901-26098-2-git-send-email-dcashman@android.com> References: <1447886901-26098-1-git-send-email-dcashman@android.com> <1447886901-26098-2-git-send-email-dcashman@android.com> Date: Wed, 18 Nov 2015 15:18:07 -0800 X-Google-Sender-Auth: z8hSgpu37F4klBj7dhJBlIjURi4 Message-ID: Subject: Re: [PATCH 1/4] mm: mmap: Add new /proc tunable for mmap_base ASLR. From: Kees Cook 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 , Catalin Marinas , Will Deacon , "H. Peter Anvin" , "x86@kernel.org" , Hector Marco , Borislav Petkov , Daniel Cashman 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: 8939 Lines: 242 On Wed, Nov 18, 2015 at 2:48 PM, Daniel Cashman wrote: > From: dcashman > > ASLR currently only uses 8 bits to generate the random offset for the > mmap base address on 32 bit architectures. This value was chosen to > prevent a poorly chosen value from dividing the address space in such > a way as to prevent large allocations. This may not be an issue on all > platforms. Allow the specification of a minimum number of bits so that > platforms desiring greater ASLR protection may determine where to place > the trade-off. > > Signed-off-by: Daniel Cashman > --- > Documentation/sysctl/vm.txt | 29 ++++++++++++++++++++ > arch/Kconfig | 64 +++++++++++++++++++++++++++++++++++++++++++++ > include/linux/mm.h | 11 ++++++++ > kernel/sysctl.c | 22 ++++++++++++++++ > mm/mmap.c | 12 +++++++++ > 5 files changed, 138 insertions(+) > > diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt > index f72370b..d77a81a 100644 > --- a/Documentation/sysctl/vm.txt > +++ b/Documentation/sysctl/vm.txt > @@ -42,6 +42,8 @@ Currently, these files are in /proc/sys/vm: > - min_slab_ratio > - min_unmapped_ratio > - mmap_min_addr > +- mmap_rnd_bits > +- mmap_rnd_compat_bits > - nr_hugepages > - nr_overcommit_hugepages > - nr_trim_pages (only if CONFIG_MMU=n) > @@ -485,6 +487,33 @@ against future potential kernel bugs. > > ============================================================== > > +mmap_rnd_bits: > + > +This value can be used to select the number of bits to use to > +determine the random offset to the base address of vma regions > +resulting from mmap allocations on architectures which support > +tuning address space randomization. This value will be bounded > +by the architecture's minimum and maximum supported values. > + > +This value can be changed after boot using the > +/proc/sys/kernel/mmap_rnd_bits tunable Here and several places below also need the swap from "/proc/sys/kernel/..." to ".../vm/...". > + > +============================================================== > + > +mmap_rnd_compat_bits: > + > +This value can be used to select the number of bits to use to > +determine the random offset to the base address of vma regions > +resulting from mmap allocations for applications run in > +compatibility mode on architectures which support tuning address > +space randomization. This value will be bounded by the > +architecture's minimum and maximum supported values. > + > +This value can be changed after boot using the > +/proc/sys/kernel/mmap_rnd_compat_bits tunable > + > +============================================================== > + > nr_hugepages > > Change the minimum size of the hugepage pool. > diff --git a/arch/Kconfig b/arch/Kconfig > index 4e949e5..141823f 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -511,6 +511,70 @@ config ARCH_HAS_ELF_RANDOMIZE > - arch_mmap_rnd() > - arch_randomize_brk() > > +config HAVE_ARCH_MMAP_RND_BITS > + bool > + help > + An arch should select this symbol if it supports setting a variable > + number of bits for use in establishing the base address for mmap > + allocations and provides values for both: > + - ARCH_MMAP_RND_BITS_MIN > + - ARCH_MMAP_RND_BITS_MAX > + > +config ARCH_MMAP_RND_BITS_MIN > + int > + > +config ARCH_MMAP_RND_BITS_MAX > + int > + > +config ARCH_MMAP_RND_BITS_DEFAULT > + int > + > +config ARCH_MMAP_RND_BITS > + int "Number of bits to use for ASLR of mmap base address" if EXPERT > + range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX > + default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT > + default ARCH_MMAP_RND_BITS_MIN > + depends on HAVE_ARCH_MMAP_RND_BITS > + help > + This value can be used to select the number of bits to use to > + determine the random offset to the base address of vma regions > + resulting from mmap allocations. This value will be bounded > + by the architecture's minimum and maximum supported values. > + > + This value can be changed after boot using the > + /proc/sys/kernel/mmap_rnd_bits tunable > + > +config HAVE_ARCH_MMAP_RND_COMPAT_BITS > + bool > + help > + An arch should select this symbol if it supports running applications > + in compatibility mode, supports setting a variable number of bits for > + use in establishing the base address for mmap allocations, and > + provides values for both: > + - ARCH_MMAP_RND_COMPAT_BITS_MIN > + - ARCH_MMAP_RND_COMPAT_BITS_MAX > + > +config ARCH_MMAP_RND_COMPAT_BITS_MIN > + int > + > +config ARCH_MMAP_RND_COMPAT_BITS_MAX > + int > + > +config ARCH_MMAP_RND_COMPAT_BITS > + int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT > + range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX > + default ARCH_MMAP_RND_COMPAT_BITS_MIN > + depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS > + help > + This value can be used to select the number of bits to use to > + determine the random offset to the base address of vma regions > + resulting from mmap allocations for compatible applications This > + value will be bounded by the architecture's minimum and maximum > + supported values. > + > + This value can be changed after boot using the > + /proc/sys/kernel/mmap_rnd_compat_bits tunable > + > config HAVE_COPY_THREAD_TLS > bool > help > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 00bad77..7d39828 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -51,6 +51,17 @@ extern int sysctl_legacy_va_layout; > #define sysctl_legacy_va_layout 0 > #endif > > +#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS > +extern int mmap_rnd_bits_min; > +extern int mmap_rnd_bits_max; > +extern int mmap_rnd_bits; > +#endif > +#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS > +extern int mmap_rnd_compat_bits_min; > +extern int mmap_rnd_compat_bits_max; > +extern int mmap_rnd_compat_bits; > +#endif > + > #include > #include > #include > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index dc6858d..40e5de6 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -1568,6 +1568,28 @@ static struct ctl_table vm_table[] = { > .mode = 0644, > .proc_handler = proc_doulongvec_minmax, > }, > +#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS > + { > + .procname = "mmap_rnd_bits", > + .data = &mmap_rnd_bits, > + .maxlen = sizeof(mmap_rnd_bits), > + .mode = 0644, > + .proc_handler = proc_dointvec_minmax, > + .extra1 = &mmap_rnd_bits_min, > + .extra2 = &mmap_rnd_bits_max, > + }, > +#endif > +#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS > + { > + .procname = "mmap_rnd_compat_bits", > + .data = &mmap_rnd_compat_bits, > + .maxlen = sizeof(mmap_rnd_compat_bits), > + .mode = 0644, > + .proc_handler = proc_dointvec_minmax, > + .extra1 = &mmap_rnd_compat_bits_min, > + .extra2 = &mmap_rnd_compat_bits_max, > + }, > +#endif > { } > }; > > diff --git a/mm/mmap.c b/mm/mmap.c > index 2ce04a6..aa49841 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -58,6 +58,18 @@ > #define arch_rebalance_pgtables(addr, len) (addr) > #endif > > +#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS > +int mmap_rnd_bits_min = CONFIG_ARCH_MMAP_RND_BITS_MIN; > +int mmap_rnd_bits_max = CONFIG_ARCH_MMAP_RND_BITS_MAX; > +int mmap_rnd_bits = CONFIG_ARCH_MMAP_RND_BITS; > +#endif > +#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS > +int mmap_rnd_compat_bits_min = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MIN; > +int mmap_rnd_compat_bits_max = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MAX; I think the min/max values should be const, since they're determined at build time and should never change. > +int mmap_rnd_compat_bits = CONFIG_ARCH_MMAP_RND_COMPAT_BITS; > +#endif > + > + > static void unmap_region(struct mm_struct *mm, > struct vm_area_struct *vma, struct vm_area_struct *prev, > unsigned long start, unsigned long end); > -- > 2.6.0.rc2.230.g3dd15c0 > -Kees -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/