[RFC PATCH v2 1/2] Randomization of address chosen by mmap.

Ilya Smith
2018-03-22T16:36:37Z

Signed-off-by: Ilya Smith <blackzert@gmail.com>
---
include/linux/mm.h | 16 ++++--
mm/mmap.c | 164 +++++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 175 insertions(+), 5 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ad06d42..c716257 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -25,6 +25,7 @@
#include <linux/err.h>
#include <linux/page_ref.h>
#include <linux/memremap.h>
+#include <linux/sched.h>

struct mempolicy;
struct anon_vma;
@@ -2253,6 +2254,13 @@ struct vm_unmapped_area_info {
unsigned long align_offset;
};

+#ifndef CONFIG_MMU
+#define randomize_va_space 0
+#else
+extern int randomize_va_space;
+#endif
+
+extern unsigned long unmapped_area_random(struct vm_unmapped_area_info *info);
extern unsigned long unmapped_area(struct vm_unmapped_area_info *info);
extern unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info);

@@ -2268,6 +2276,9 @@ extern unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info);
static inline unsigned long
vm_unmapped_area(struct vm_unmapped_area_info *info)
{
+ /* How about 32 bit process?? */
+ if ((current->flags & PF_RANDOMIZE) && randomize_va_space > 3)
+ return unmapped_area_random(info);
if (info->flags & VM_UNMAPPED_AREA_TOPDOWN)
return unmapped_area_topdown(info);
else
@@ -2529,11 +2540,6 @@ int drop_caches_sysctl_handler(struct ctl_table *, int,
void drop_slab(void);
void drop_slab_node(int nid);

-#ifndef CONFIG_MMU
-#define randomize_va_space 0
-#else
-extern int randomize_va_space;
-#endif

const char * arch_vma_name(struct vm_area_struct *vma);
void print_vma_addr(char *prefix, unsigned long rip);
diff --git a/mm/mmap.c b/mm/mmap.c
index 9efdc021..ba9cebb 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -45,6 +45,7 @@
#include <linux/moduleparam.h>
#include <linux/pkeys.h>
#include <linux/oom.h>
+#include <linux/random.h>

#include <linux/uaccess.h>
#include <asm/cacheflush.h>
@@ -1780,6 +1781,169 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
return error;
}

+unsigned long unmapped_area_random(struct vm_unmapped_area_info *info)
+{
+ struct mm_struct *mm = current->mm;
+ struct vm_area_struct *vma = NULL;
+ struct vm_area_struct *visited_vma = NULL;
+ unsigned long entropy[2];
+ unsigned long length, low_limit, high_limit, gap_start, gap_end;
+ unsigned long addr = 0;
+
+ /* get entropy with prng */
+ prandom_bytes(&entropy, sizeof(entropy));
+ /* small hack to prevent EPERM result */
+ info->low_limit = max(info->low_limit, mmap_min_addr);
+
+ /* Adjust search length to account for worst case alignment overhead */
+ length = info->length + info->align_mask;
+ if (length < info->length)
+ return -ENOMEM;
+
+ /*
+ * Adjust search limits by the desired length.
+ * See implementation comment at top of unmapped_area().
+ */
+ gap_end = info->high_limit;
+ if (gap_end < length)
+ return -ENOMEM;
+ high_limit = gap_end - length;
+
+ low_limit = info->low_limit + info->align_mask;
+ if (low_limit >= high_limit)
+ return -ENOMEM;
+
+ /* Choose random addr in limit range */
+ addr = entropy[0] % ((high_limit - low_limit) >> PAGE_SHIFT);
+ addr = low_limit + (addr << PAGE_SHIFT);
+ addr += (info->align_offset - addr) & info->align_mask;
+
+ /* Check if rbtree root looks promising */
+ if (RB_EMPTY_ROOT(&mm->mm_rb))
+ return -ENOMEM;
+
+ vma = rb_entry(mm->mm_rb.rb_node, struct vm_area_struct, vm_rb);
+ if (vma->rb_subtree_gap < length)
+ return -ENOMEM;
+ /* use randomly chosen address to find closest suitable gap */
+ while (true) {
+ gap_start = vma->vm_prev ? vm_end_gap(vma->vm_prev) : 0;
+ gap_end = vm_start_gap(vma);
+ if (gap_end < low_limit)
+ break;
+ if (addr < vm_start_gap(vma)) {
+ /* random said check left */
+ if (vma->vm_rb.rb_left) {
+ struct vm_area_struct *left + rb_entry(vma->vm_rb.rb_left,
+ struct vm_area_struct, vm_rb);
+ if (addr <= vm_start_gap(left) &&
+ left->rb_subtree_gap >= length) {
+ vma = left;
+ continue;
+ }
+ }
+ } else if (addr >= vm_end_gap(vma)) {
+ /* random said check right */
+ if (vma->vm_rb.rb_right) {
+ struct vm_area_struct *right + rb_entry(vma->vm_rb.rb_right,
+ struct vm_area_struct, vm_rb);
+ /* it want go to the right */
+ if (right->rb_subtree_gap >= length) {
+ vma = right;
+ continue;
+ }
+ }
+ }
+ if (gap_start < low_limit) {
+ if (gap_end <= low_limit)
+ break;
+ gap_start = low_limit;
+ } else if (gap_end > info->high_limit) {
+ if (gap_start >= info->high_limit)
+ break;
+ gap_end = info->high_limit;
+ }
+ if (gap_end > gap_start &&
+ gap_end - gap_start >= length)
+ goto found;
+ visited_vma = vma;
+ break;
+ }
+ /* not found */
+ while (true) {
+ gap_start = vma->vm_prev ? vm_end_gap(vma->vm_prev) : 0;
+
+ if (gap_start <= high_limit && vma->vm_rb.rb_right) {
+ struct vm_area_struct *right + rb_entry(vma->vm_rb.rb_right,
+ struct vm_area_struct, vm_rb);
+ if (right->rb_subtree_gap >= length &&
+ right != visited_vma) {
+ vma = right;
+ continue;
+ }
+ }
+
+check_current:
+ /* Check if current node has a suitable gap */
+ gap_end = vm_start_gap(vma);
+ if (gap_end <= low_limit)
+ goto go_back;
+
+ if (gap_start < low_limit)
+ gap_start = low_limit;
+
+ if (gap_start <= high_limit &&
+ gap_end > gap_start && gap_end - gap_start >= length)
+ goto found;
+
+ /* Visit left subtree if it looks promising */
+ if (vma->vm_rb.rb_left) {
+ struct vm_area_struct *left + rb_entry(vma->vm_rb.rb_left,
+ struct vm_area_struct, vm_rb);
+ if (left->rb_subtree_gap >= length &&
+ vm_end_gap(left) > low_limit &&
+ left != visited_vma) {
+ vma = left;
+ continue;
+ }
+ }
+go_back:
+ /* Go back up the rbtree to find next candidate node */
+ while (true) {
+ struct rb_node *prev = &vma->vm_rb;
+
+ if (!rb_parent(prev))
+ return -ENOMEM;
+ visited_vma = vma;
+ vma = rb_entry(rb_parent(prev),
+ struct vm_area_struct, vm_rb);
+ if (prev = vma->vm_rb.rb_right) {
+ gap_start = vma->vm_prev ?
+ vm_end_gap(vma->vm_prev) : low_limit;
+ goto check_current;
+ }
+ }
+ }
+found:
+ /* We found a suitable gap. Clip it with the original high_limit. */
+ if (gap_end > info->high_limit)
+ gap_end = info->high_limit;
+ gap_end -= info->length;
+ gap_end -= (gap_end - info->align_offset) & info->align_mask;
+ /* only one suitable page */
+ if (gap_end = gap_start)
+ return gap_start;
+ addr = entropy[1] % (min((gap_end - gap_start) >> PAGE_SHIFT,
+ 0x10000UL));
+ addr = gap_end - (addr << PAGE_SHIFT);
+ addr += (info->align_offset - addr) & info->align_mask;
+ return addr;
+}
+
unsigned long unmapped_area(struct vm_unmapped_area_info *info)
{
/*
--
2.7.4