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

Christophe Leroy
2021-11-22T08:49:15Z

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.leroy@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