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

... 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: 1e133ab296f3 ("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>

diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index e0735c3..d63c0cc 100644 (file)
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -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);