powerpc: 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.

(Can mmap ASLR be safely enabled in the legacy mmap case here?  Other
archs use "mm->mmap_base = TASK_UNMAPPED_BASE + random_factor".)

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/powerpc/mm/mmap.c b/arch/powerpc/mm/mmap.c
index cb8bdbe4972fa8bbe4c63039537ab9cbd4ccb233..1ad2299d795dd0689d2f693b80b928f8d52c3bd2 100644 (file)
--- a/arch/powerpc/mm/mmap.c
+++ b/arch/powerpc/mm/mmap.c
@@ -55,19 +55,18 @@ static inline int mmap_is_legacy(void)
 
 static unsigned long mmap_rnd(void)
 {
-       unsigned long rnd = 0;
+       unsigned long rnd;
+
+       /* 8MB for 32bit, 1GB for 64bit */
+       if (is_32bit_task())
+               rnd = (unsigned long)get_random_int() % (1<<(23-PAGE_SHIFT));
+       else
+               rnd = (unsigned long)get_random_int() % (1<<(30-PAGE_SHIFT));
 
-       if (current->flags & PF_RANDOMIZE) {
-               /* 8MB for 32bit, 1GB for 64bit */
-               if (is_32bit_task())
-                       rnd = (long)(get_random_int() % (1<<(23-PAGE_SHIFT)));
-               else
-                       rnd = (long)(get_random_int() % (1<<(30-PAGE_SHIFT)));
-       }
        return rnd << PAGE_SHIFT;
 }
 
-static inline unsigned long mmap_base(void)
+static inline unsigned long mmap_base(unsigned long rnd)
 {
        unsigned long gap = rlimit(RLIMIT_STACK);
 
@@ -76,7 +75,7 @@ static inline unsigned long mmap_base(void)
        else if (gap > MAX_GAP)
                gap = MAX_GAP;
 
-       return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd());
+       return PAGE_ALIGN(TASK_SIZE - gap - rnd);
 }
 
 /*
@@ -85,6 +84,11 @@ static inline unsigned long mmap_base(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:
@@ -93,7 +97,7 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
                mm->mmap_base = TASK_UNMAPPED_BASE;
                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;
        }
 }