linux-kernel - [PATCH 4.9 109/207] s390/gmap: dont unconditionally call pte_unmap_unlock() in __gmap

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Date:   Wed, 24 Nov 2021 12:56:20 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, David Hildenbrand <david@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 109/207] s390/gmap: dont unconditionally call pte_unmap_unlock() in __gmap_zap()

From: David Hildenbrand <david@...hat.com>

[ 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@...hat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
Acked-by: Heiko Carstens <hca@...ux.ibm.com>
Link: https://lore.kernel.org/r/20210909162248.14969-3-david@redhat.com
Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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);