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s390/gmap: don't unconditionally call pte_unmap_unlock() in __gmap_zap()

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... otherwise we will try unlocking a spinlock that was never locked via a
garbage pointer.

At the time we reach this code path, we usually successfully looked up
a PGSTE already; however, evil user space could have manipulated the VMA
layout in the meantime and triggered removal of the page table.

Fixes: 1e133ab296 ("s390/mm: split arch/s390/mm/pgtable.c")
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Link: https://lore.kernel.org/r/20210909162248.14969-3-david@redhat.com
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
This commit is contained in:
David Hildenbrand 2021-09-09 18:22:41 +02:00 committed by Christian Borntraeger
parent 2d8fb8f391
commit b159f94c86
1 changed files with 3 additions and 2 deletions
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5
arch/s390/mm/gmap.c
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@ -689,9 +689,10 @@ void __gmap_zap(struct gmap *gmap, unsigned long gaddr)
/* Get pointer to the page table entry */
ptep = get_locked_pte(gmap->mm, vmaddr, &ptl);
if (likely(ptep))
if (likely(ptep)) {
ptep_zap_unused(gmap->mm, vmaddr, ptep, 0);
pte_unmap_unlock(ptep, ptl);
pte_unmap_unlock(ptep, ptl);
}
}
}
EXPORT_SYMBOL_GPL(__gmap_zap);