diff options
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/Kconfig | 18 | ||||
| -rw-r--r-- | mm/mmap.c | 3 |
2 files changed, 21 insertions, 0 deletions
diff --git a/mm/Kconfig b/mm/Kconfig index a5b77811fdf2..54c5251794b4 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -216,3 +216,21 @@ config UNEVICTABLE_LRU config MMU_NOTIFIER bool + +config DEFAULT_MMAP_MIN_ADDR + 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. diff --git a/mm/mmap.c b/mm/mmap.c index 00ced3ee49a8..fa9ef7afeee6 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -86,6 +86,9 @@ int sysctl_overcommit_ratio = 50; /* default is 50% */ int sysctl_max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT; atomic_long_t vm_committed_space = ATOMIC_LONG_INIT(0); +/* 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 |