FROMLIST: mm: mmap: Add new /proc tunable for mmap_base ASLR.

(cherry picked from commit https://lkml.org/lkml/2015/12/21/337)

ASLR  only uses as few as 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.

Bug: 24047224
Signed-off-by: Daniel Cashman <dcashman@android.com>
Signed-off-by: Daniel Cashman <dcashman@google.com>
Change-Id: Ic74424e07710cd9ccb4a02871a829d14ef0cc4bc

diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index b81fca90f7fe4acdaaf2f07682696294e4472b4e..c7539eced626305cddd76611af7759a46e12dd13 100644 (file)
--- 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)
@@ -455,6 +457,33 @@ 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/vm/mmap_rnd_bits tunable
+
+==============================================================
+
+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/vm/mmap_rnd_compat_bits tunable
+
+==============================================================
+
 nr_hugepages
 
 Change the minimum size of the hugepage pool.

diff --git a/arch/Kconfig b/arch/Kconfig
index 4c0a1d03ae0d82940ac6328ebbd8fba3c32c3d67..6dbcfc4fc54ceb53d43de3e8172bac10c93f1197 100644 (file)
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -391,6 +391,74 @@ config HAVE_UNDERSCORE_SYMBOL_PREFIX
          Some architectures generate an _ in front of C symbols; things like
          module loading and assembly files need to know about this.
 
+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, has MMU enabled 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/vm/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, has MMU
+         enabled 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_DEFAULT
+       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_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
+       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/vm/mmap_rnd_compat_bits tunable
+
 #
 # ABI hall of shame
 #

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 9fe6bc3e5527821010e24c8bb10bce8c575a4788..06f4ed811b2abf06ccd2192ad2ce3dd417c21130 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -40,6 +40,17 @@ extern int sysctl_legacy_va_layout;
 #define sysctl_legacy_va_layout 0
 #endif
 
+#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
+extern const int mmap_rnd_bits_min;
+extern const int mmap_rnd_bits_max;
+extern int mmap_rnd_bits __read_mostly;
+#endif
+#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS
+extern const int mmap_rnd_compat_bits_min;
+extern const int mmap_rnd_compat_bits_max;
+extern int mmap_rnd_compat_bits __read_mostly;
+#endif
+
 #include <asm/page.h>
 #include <asm/pgtable.h>
 #include <asm/processor.h>

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index f9648251352d5177b16d632047da3b0cd4b1d8e8..3718b15fd5f7088f8fc2812084a6771e2c080c96 100644 (file)
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1476,6 +1476,28 @@ 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           = 0600,
+               .proc_handler   = proc_dointvec_minmax,
+               .extra1         = (void *)&mmap_rnd_bits_min,
+               .extra2         = (void *)&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           = 0600,
+               .proc_handler   = proc_dointvec_minmax,
+               .extra1         = (void *)&mmap_rnd_compat_bits_min,
+               .extra2         = (void *)&mmap_rnd_compat_bits_max,
+       },
+#endif
        { }
 };
 

diff --git a/mm/mmap.c b/mm/mmap.c
index 5d7dc16f9b83200f33d8b432e2f98aacca227d25..49cb9f0ebeebc51030611d4c40dbfcca1ae7859c 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -52,6 +52,17 @@
 #define arch_rebalance_pgtables(addr, len)             (addr)
 #endif
 
+#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
+const int mmap_rnd_bits_min = CONFIG_ARCH_MMAP_RND_BITS_MIN;
+const int mmap_rnd_bits_max = CONFIG_ARCH_MMAP_RND_BITS_MAX;
+int mmap_rnd_bits __read_mostly = CONFIG_ARCH_MMAP_RND_BITS;
+#endif
+#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS
+const int mmap_rnd_compat_bits_min = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MIN;
+const int mmap_rnd_compat_bits_max = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MAX;
+int mmap_rnd_compat_bits __read_mostly = 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);