s390: standardize mmap_rnd() usage

In preparation for splitting out ET_DYN ASLR, this refactors the use of
mmap_rnd() to be used similarly to arm and x86, and extracts the
checking of PF_RANDOMIZE.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 23 insertions, 11 deletions

diff --git a/arch/s390/mm/mmap.c b/arch/s390/mm/mmap.c
index 179a2c20b01f..db57078075c5 100644
--- a/arch/s390/mm/mmap.c
+++ b/arch/s390/mm/mmap.c
@@ -62,20 +62,18 @@ static inline int mmap_is_legacy(void)
 
 static unsigned long mmap_rnd(void)
 {
-        if (!(current->flags & PF_RANDOMIZE))
-                return 0;
         if (is_32bit_task())
                 return (get_random_int() & 0x7ff) << PAGE_SHIFT;
         else
                 return (get_random_int() & mmap_rnd_mask) << PAGE_SHIFT;
 }
 
-static unsigned long mmap_base_legacy(void)
+static unsigned long mmap_base_legacy(unsigned long rnd)
 {
-        return TASK_UNMAPPED_BASE + mmap_rnd();
+        return TASK_UNMAPPED_BASE + rnd;
 }
 
-static inline unsigned long mmap_base(void)
+static inline unsigned long mmap_base(unsigned long rnd)
 {
         unsigned long gap = rlimit(RLIMIT_STACK);
 
@@ -84,7 +82,7 @@ static inline unsigned long mmap_base(void)
         else if (gap > MAX_GAP)
                 gap = MAX_GAP;
         gap &= PAGE_MASK;
-        return STACK_TOP - stack_maxrandom_size() - mmap_rnd() - gap;
+        return STACK_TOP - stack_maxrandom_size() - rnd - gap;
 }
 
 unsigned long
@@ -187,7 +185,11 @@ unsigned long randomize_et_dyn(void)
         if (!is_32bit_task())
                 /* Align to 4GB */
                 base &= ~((1UL << 32) - 1);
-        return base + mmap_rnd();
+
+        if (current->flags & PF_RANDOMIZE)
+                base += mmap_rnd();
+
+        return base;
 }
 
 #ifndef CONFIG_64BIT
@@ -198,15 +200,20 @@ unsigned long randomize_et_dyn(void)
  */
 void arch_pick_mmap_layout(struct mm_struct *mm)
 {
+        unsigned long random_factor = 0UL;
+
+        if (current->flags & PF_RANDOMIZE)
+                random_factor = mmap_rnd();
+
         /*
          * Fall back to the standard layout if the personality
          * bit is set, or if the expected stack growth is unlimited:
          */
         if (mmap_is_legacy()) {
-                mm->mmap_base = mmap_base_legacy();
+                mm->mmap_base = mmap_base_legacy(random_factor);
                 mm->get_unmapped_area = arch_get_unmapped_area;
         } else {
-                mm->mmap_base = mmap_base();
+                mm->mmap_base = mmap_base(random_factor);
                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
         }
 }
@@ -273,15 +280,20 @@ s390_get_unmapped_area_topdown(struct file *filp, const unsigned long addr,
  */
 void arch_pick_mmap_layout(struct mm_struct *mm)
 {
+        unsigned long random_factor = 0UL;
+
+        if (current->flags & PF_RANDOMIZE)
+                random_factor = mmap_rnd();
+
         /*
          * Fall back to the standard layout if the personality
          * bit is set, or if the expected stack growth is unlimited:
          */
         if (mmap_is_legacy()) {
-                mm->mmap_base = mmap_base_legacy();
+                mm->mmap_base = mmap_base_legacy(random_factor);
                 mm->get_unmapped_area = s390_get_unmapped_area;
         } else {
-                mm->mmap_base = mmap_base();
+                mm->mmap_base = mmap_base(random_factor);
                 mm->get_unmapped_area = s390_get_unmapped_area_topdown;
         }
 }