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

From: Greg Kroah-Hartman
Date: Fri Oct 03 2014 - 17:51:25 EST


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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