[PATCH 3.16 210/357] KVM: s390/mm: try a cow on read only pages for key ops

[Greg Kroah-Hartman]

3.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christian Borntraeger <borntraeger@xxxxxxxxxx>

commit ab3f285f227fec62868037e9b1b1fd18294a83b8 upstream.

The PFMF instruction handler  blindly wrote the storage key even if
the page was mapped R/O in the host. Lets try a COW before continuing
and bail out in case of errors.

Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Reviewed-by: Dominik Dingel <dingel@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/s390/mm/pgtable.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -986,11 +986,21 @@ int set_guest_storage_key(struct mm_stru
 	pte_t *ptep;
 
 	down_read(&mm->mmap_sem);
+retry:
 	ptep = get_locked_pte(current->mm, addr, &ptl);
 	if (unlikely(!ptep)) {
 		up_read(&mm->mmap_sem);
 		return -EFAULT;
 	}
+	if (!(pte_val(*ptep) & _PAGE_INVALID) &&
+	     (pte_val(*ptep) & _PAGE_PROTECT)) {
+			pte_unmap_unlock(*ptep, ptl);
+			if (fixup_user_fault(current, mm, addr, FAULT_FLAG_WRITE)) {
+				up_read(&mm->mmap_sem);
+				return -EFAULT;
+			}
+			goto retry;
+		}
 
 	new = old = pgste_get_lock(ptep);
 	pgste_val(new) &= ~(PGSTE_GR_BIT | PGSTE_GC_BIT |


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