mips: extract logic for mmap_rnd()

In preparation for splitting out ET_DYN ASLR, extract the mmap ASLR
selection into a separate function.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 8 deletions

diff --git a/arch/mips/mm/mmap.c b/arch/mips/mm/mmap.c
index f1baadd56e82..9a4f1f5c1f0e 100644
--- a/arch/mips/mm/mmap.c
+++ b/arch/mips/mm/mmap.c
@@ -142,18 +142,26 @@ unsigned long arch_get_unmapped_area_topdown(struct file *filp,
                         addr0, len, pgoff, flags, DOWN);
 }
 
+static unsigned long mmap_rnd(void)
+{
+        unsigned long rnd;
+
+        rnd = (unsigned long)get_random_int();
+        rnd <<= PAGE_SHIFT;
+        if (TASK_IS_32BIT_ADDR)
+                rnd &= 0xfffffful;
+        else
+                rnd &= 0xffffffful;
+
+        return rnd;
+}
+
 void arch_pick_mmap_layout(struct mm_struct *mm)
 {
         unsigned long random_factor = 0UL;
 
-        if (current->flags & PF_RANDOMIZE) {
-                random_factor = get_random_int();
-                random_factor = random_factor << PAGE_SHIFT;
-                if (TASK_IS_32BIT_ADDR)
-                        random_factor &= 0xfffffful;
-                else
-                        random_factor &= 0xffffffful;
-        }
+        if (current->flags & PF_RANDOMIZE)
+                random_factor = mmap_rnd();
 
         if (mmap_is_legacy()) {
                 mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;