[PATCH 4.9 109/207] s390/gmap: dont unconditionally call pte_unmap_unlock() in __gmap_zap()

[Greg Kroah-Hartman]

From: David Hildenbrand <david@xxxxxxxxxx>

[ Upstream commit b159f94c86b43cf7e73e654bc527255b1f4eafc4 ]

... 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@xxxxxxxxxx>
Reviewed-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
Acked-by: Heiko Carstens <hca@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210909162248.14969-3-david@xxxxxxxxxx
Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 arch/s390/mm/gmap.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -662,9 +662,10 @@ void __gmap_zap(struct gmap *gmap, unsig
 		vmaddr |= gaddr & ~PMD_MASK;
 		/* 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);