KVM: s390/mm: try a cow on read only pages for key ops

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@de.ibm.com>
Reviewed-by: Dominik Dingel <dingel@linux.vnet.ibm.com>
Cc: stable@vger.kernel.org

diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 19daa53..5404a62 100644 (file)
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -986,11 +986,21 @@ int set_guest_storage_key(struct mm_struct *mm, unsigned long addr,
        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 |