From: dcashman <dcash...@google.com>
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 <dcash...@google.com>
---
Changes in v2:
- Added HAVE_ARCH_MMAP_RND_BITS as Kconfig boolean selector.
- Moved ARCH_MMAP_RND_BITS_MIN, ARCH_MMAP_RND_BITS_MAX, and
ARCH_MMAP_RND_BITS declarations to arch/Kconfig instead of relying
soley on arch-specific Kconfigs.
- Moved definition of mmap_rnd_bits_min, mmap_rnd_bits_max and
mmap_rnd_bits to mm/mmap.c instead of relying solely on arch-specific
code.
Documentation/sysctl/kernel.txt | 14 ++++++++++++++
arch/Kconfig | 29 +++++++++++++++++++++++++++++
include/linux/mm.h | 6 ++++++
kernel/sysctl.c | 11 +++++++++++
mm/mmap.c | 6 ++++++
5 files changed, 66 insertions(+)
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index 6fccb69..0d4ca53 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -41,6 +41,7 @@ show up in /proc/sys/kernel:
- kptr_restrict
- kstack_depth_to_print [ X86 only ]
- l2cr [ PPC only ]
+- mmap_rnd_bits
- modprobe ==> Documentation/debugging-modules.txt
- modules_disabled
- msg_next_id [ sysv ipc ]
@@ -391,6 +392,19 @@ This flag controls the L2 cache of G3 processor boards. If
==============================================================
+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
+
+==============================================================
+
modules_disabled:
A toggle value indicating if modules are allowed to be loaded
diff --git a/arch/Kconfig b/arch/Kconfig
index 4e949e5..2133973 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -511,6 +511,35 @@ 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
+ 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_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_COPY_THREAD_TLS
bool
help
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 80001de..ee209c1 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -51,6 +51,12 @@ 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
+
#include <asm/page.h>
#include <asm/pgtable.h>
#include <asm/processor.h>
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index e69201d..276da8b 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1139,6 +1139,17 @@ static struct ctl_table kern_table[] = {
.proc_handler = timer_migration_handler,
},
#endif
+#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
{ }
};
diff --git a/mm/mmap.c b/mm/mmap.c
index 79bcc9f..264aa8e 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -58,6 +58,12 @@
#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
+
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
--
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