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

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Message-Id: <0ee9001d347a2b7017cea9881663201f4f660484.1637570556.git.christophe.leroy@csgroup.eu>
Date:   Mon, 22 Nov 2021 09:48:28 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, alex@...ti.fr
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-mm@...ck.org
Subject: [PATCH 8/8] powerpc/mm: Properly randomise mmap with slices

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@...roup.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