[PATCH v4 06/10] s390: standardize mmap_rnd() usage

[Kees Cook]

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 <keesc...@chromium.org>
---
 arch/s390/mm/mmap.c | 34 +++++++++++++++++++++++-----------
 1 file 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;
        }
 }
-- 
1.9.1

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