[PATCH 8/8] powerpc/mm: Properly randomise mmap with slices

[Christophe Leroy]

Now that powerpc switched to default topdown mmap layout,
mm->mmap_base is properly randomised.  However
slice_find_area_bottomup() doesn't use mm->mmap_base but
uses the fixed TASK_UNMAPPED_BASE instead.

slice_find_area_bottomup() being used as a fallback to
slice_find_area_topdown(), it can't use mm->mmap_base
directly.

Instead of always using TASK_UNMAPPED_BASE as base address, leave
it to the caller. When called from slice_find_area_topdown()
TASK_UNMAPPED_BASE is used. Otherwise mm->mmap_base is used.

Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu>
---
 arch/powerpc/mm/book3s64/slice.c | 18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/mm/book3s64/slice.c b/arch/powerpc/mm/book3s64/slice.c
index 8327a43d29cb..0fef63763e6d 100644
--- a/arch/powerpc/mm/book3s64/slice.c
+++ b/arch/powerpc/mm/book3s64/slice.c
@@ -276,20 +276,18 @@ static bool slice_scan_available(unsigned long addr,
 }
 
 static unsigned long slice_find_area_bottomup(struct mm_struct *mm,
-                                             unsigned long len,
+                                             unsigned long addr, unsigned long 
len,
                                              const struct slice_mask 
*available,
                                              int psize, unsigned long 
high_limit)
 {
        int pshift = max_t(int, mmu_psize_defs[psize].shift, PAGE_SHIFT);
-       unsigned long addr, found, next_end;
+       unsigned long found, next_end;
        struct vm_unmapped_area_info info;
 
        info.flags = 0;
        info.length = len;
        info.align_mask = PAGE_MASK & ((1ul << pshift) - 1);
        info.align_offset = 0;
-
-       addr = TASK_UNMAPPED_BASE;
        /*
         * Check till the allow max value for this mmap request
         */
@@ -322,12 +320,12 @@ static unsigned long slice_find_area_bottomup(struct 
mm_struct *mm,
 }
 
 static unsigned long slice_find_area_topdown(struct mm_struct *mm,
-                                            unsigned long len,
+                                            unsigned long addr, unsigned long 
len,
                                             const struct slice_mask *available,
                                             int psize, unsigned long 
high_limit)
 {
        int pshift = max_t(int, mmu_psize_defs[psize].shift, PAGE_SHIFT);
-       unsigned long addr, found, prev;
+       unsigned long found, prev;
        struct vm_unmapped_area_info info;
        unsigned long min_addr = max(PAGE_SIZE, mmap_min_addr);
 
@@ -335,8 +333,6 @@ static unsigned long slice_find_area_topdown(struct 
mm_struct *mm,
        info.length = len;
        info.align_mask = PAGE_MASK & ((1ul << pshift) - 1);
        info.align_offset = 0;
-
-       addr = mm->mmap_base;
        /*
         * If we are trying to allocate above DEFAULT_MAP_WINDOW
         * Add the different to the mmap_base.
@@ -377,7 +373,7 @@ static unsigned long slice_find_area_topdown(struct 
mm_struct *mm,
         * can happen with large stack limits and large mmap()
         * allocations.
         */
-       return slice_find_area_bottomup(mm, len, available, psize, high_limit);
+       return slice_find_area_bottomup(mm, TASK_UNMAPPED_BASE, len, available, 
psize, high_limit);
 }
 
 
@@ -386,9 +382,9 @@ static unsigned long slice_find_area(struct mm_struct *mm, 
unsigned long len,
                                     int topdown, unsigned long high_limit)
 {
        if (topdown)
-               return slice_find_area_topdown(mm, len, mask, psize, 
high_limit);
+               return slice_find_area_topdown(mm, mm->mmap_base, len, mask, 
psize, high_limit);
        else
-               return slice_find_area_bottomup(mm, len, mask, psize, 
high_limit);
+               return slice_find_area_bottomup(mm, mm->mmap_base, len, mask, 
psize, high_limit);
 }
 
 static inline void slice_copy_mask(struct slice_mask *dst,
-- 
2.33.1