4 files changed, 26 insertions, 1 deletions
diff --git a/mm/Kconfig b/mm/Kconfig
index c2b57d8..71830ba 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -226,6 +226,25 @@ config HAVE_MLOCKED_PAGE_BIT
 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.
+
+
 config NOMMU_INITIAL_TRIM_EXCESS
 	int "Turn on mmap() excess space trimming before booting"
 	depends on !MMU
diff --git a/mm/mmap.c b/mm/mmap.c
index 6b7b1a9..2b43fa1 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
diff --git a/mm/nommu.c b/mm/nommu.c
index b571ef7..2fd2ad5 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -69,6 +69,9 @@ int sysctl_max_map_count = DEFAULT_MAX_MAP_COUNT;
 int sysctl_nr_trim_pages = CONFIG_NOMMU_INITIAL_TRIM_EXCESS;
 int heap_stack_gap = 0;
 
+/* amount of vm to protect from userspace access */
+unsigned long mmap_min_addr = CONFIG_DEFAULT_MMAP_MIN_ADDR;
+
 atomic_long_t mmap_pages_allocated;
 
 EXPORT_SYMBOL(mem_map);
diff --git a/mm/shmem.c b/mm/shmem.c
index b25f95c..0132fbd 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2659,6 +2659,7 @@ struct file *shmem_file_setup(char *name, loff_t size, unsigned long flags)
 	if (error)
 		goto close_file;
 #endif
+	ima_counts_get(file);
 	return file;
 
 close_file:
@@ -2684,7 +2685,6 @@ int shmem_zero_setup(struct vm_area_struct *vma)
 	if (IS_ERR(file))
 		return PTR_ERR(file);
 
-	ima_shm_check(file);
 	if (vma->vm_file)
 		fput(vma->vm_file);
 	vma->vm_file = file;