path: root/mm
diff options
Diffstat (limited to 'mm')
2 files changed, 22 insertions, 0 deletions
diff --git a/mm/Kconfig b/mm/Kconfig
index c2b57d81e15..71830ba7b98 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -226,6 +226,25 @@ config HAVE_MLOCKED_PAGE_BIT
+ int "Low address space to protect from user allocation"
+ default 4096
+ help
+ This is the portion of low virtual memory which should be protected
+ from userspace allocation. Keeping a user from writing to low pages
+ can help reduce the impact of kernel NULL pointer bugs.
+ For most ia64, ppc64 and x86 users with lots of address space
+ a value of 65536 is reasonable and should cause no problems.
+ On arm and other archs it should not be higher than 32768.
+ Programs which use vm86 functionality would either need additional
+ permissions from either the LSM or the capabilities module or have
+ this protection disabled.
+ This value can be changed after boot using the
+ /proc/sys/vm/mmap_min_addr tunable.
int "Turn on mmap() excess space trimming before booting"
depends on !MMU
diff --git a/mm/mmap.c b/mm/mmap.c
index 6b7b1a95944..2b43fa1aa3c 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -87,6 +87,9 @@ int sysctl_overcommit_ratio = 50; /* default is 50% */
int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT;
struct percpu_counter vm_committed_as;
+/* amount of vm to protect from userspace access */
+unsigned long mmap_min_addr = CONFIG_DEFAULT_MMAP_MIN_ADDR;
* Check that a process has enough memory to allocate a new virtual
* mapping. 0 means there is enough memory for the allocation to