powerpc/mm/hash64: Zero PGD pages on allocation

[ Upstream commit fc5c2f4a55a2c258e12013cdf287cf266dbcd2a7 ]

On powerpc we allocate page table pages from slab caches of different
sizes. Currently we have a constructor that zeroes out the objects when
we allocate them for the first time.

We expect the objects to be zeroed out when we free the the object
back to slab cache. This happens in the unmap path. For hugetlb pages
we call huge_pte_get_and_clear() to do that.

With the current configuration of page table size, both PUD and PGD
level tables are allocated from the same slab cache. At the PUD level,
we use the second half of the table to store the slot information. But
we never clear that when unmapping.

When such a freed object is then allocated for a PGD page, the second
half of the page table page will not be zeroed as expected. This
results in a kernel crash.

Fix it by always clearing PGD pages when they're allocated.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
[mpe: Change log wording and formatting, add whitespace]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/powerpc/include/asm/book3s/64/pgalloc.h b/arch/powerpc/include/asm/book3s/64/pgalloc.h
index 1fcfa425cefaf205fe787cc9a480265aec758e0f..f326b40b7c7bb2884ef90708d474949d83f0621c 100644 (file)
--- a/arch/powerpc/include/asm/book3s/64/pgalloc.h
+++ b/arch/powerpc/include/asm/book3s/64/pgalloc.h
@@ -73,10 +73,16 @@ static inline void radix__pgd_free(struct mm_struct *mm, pgd_t *pgd)
 
 static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 {
+       pgd_t *pgd;
+
        if (radix_enabled())
                return radix__pgd_alloc(mm);
-       return kmem_cache_alloc(PGT_CACHE(PGD_INDEX_SIZE),
-               pgtable_gfp_flags(mm, GFP_KERNEL));
+
+       pgd = kmem_cache_alloc(PGT_CACHE(PGD_INDEX_SIZE),
+                              pgtable_gfp_flags(mm, GFP_KERNEL));
+       memset(pgd, 0, PGD_TABLE_SIZE);
+
+       return pgd;
 }
 
 static inline void pgd_free(struct mm_struct *mm, pgd_t *pgd)