s390/mm: don't fault everything in read-write in gmap_pte_op_fixup()

Let's not fault in everything in read-write but limit it to read-only
where possible.

When restricting access rights, we already have the required protection
level in our hands. When reading from guest 2 storage (gmap_read_table),
it is obviously PROT_READ. When shadowing a pte, the required protection
level is given via the guest 2 provided pte.

Based on an initial patch by Martin Schwidefsky.

Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

1 files changed, 11 insertions, 6 deletions

diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index d00e4abb559e..738d75495e56 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -811,19 +811,22 @@ static pte_t *gmap_pte_op_walk(struct gmap *gmap, unsigned long gaddr,
  * @gmap: pointer to guest mapping meta data structure
  * @gaddr: virtual address in the guest address space
  * @vmaddr: address in the host process address space
+ * @prot: indicates access rights: PROT_NONE, PROT_READ or PROT_WRITE
  *
  * Returns 0 if the caller can retry __gmap_translate (might fail again),
  * -ENOMEM if out of memory and -EFAULT if anything goes wrong while fixing
  * up or connecting the gmap page table.
  */
 static int gmap_pte_op_fixup(struct gmap *gmap, unsigned long gaddr,
-                             unsigned long vmaddr)
+                             unsigned long vmaddr, int prot)
 {
         struct mm_struct *mm = gmap->mm;
+        unsigned int fault_flags;
         bool unlocked = false;
 
         BUG_ON(gmap_is_shadow(gmap));
-        if (fixup_user_fault(current, mm, vmaddr, FAULT_FLAG_WRITE, &unlocked))
+        fault_flags = (prot == PROT_WRITE) ? FAULT_FLAG_WRITE : 0;
+        if (fixup_user_fault(current, mm, vmaddr, fault_flags, &unlocked))
                 return -EFAULT;
         if (unlocked)
                 /* lost mmap_sem, caller has to retry __gmap_translate */
@@ -875,7 +878,7 @@ static int gmap_protect_range(struct gmap *gmap, unsigned long gaddr,
                         vmaddr = __gmap_translate(gmap, gaddr);
                         if (IS_ERR_VALUE(vmaddr))
                                 return vmaddr;
-                        rc = gmap_pte_op_fixup(gmap, gaddr, vmaddr);
+                        rc = gmap_pte_op_fixup(gmap, gaddr, vmaddr, prot);
                         if (rc)
                                 return rc;
                         continue;
@@ -957,7 +960,7 @@ int gmap_read_table(struct gmap *gmap, unsigned long gaddr, unsigned long *val)
                         rc = vmaddr;
                         break;
                 }
-                rc = gmap_pte_op_fixup(gmap, gaddr, vmaddr);
+                rc = gmap_pte_op_fixup(gmap, gaddr, vmaddr, PROT_READ);
                 if (rc)
                         break;
         }
@@ -1041,7 +1044,7 @@ static int gmap_protect_rmap(struct gmap *sg, unsigned long raddr,
                 radix_tree_preload_end();
                 if (rc) {
                         kfree(rmap);
-                        rc = gmap_pte_op_fixup(parent, paddr, vmaddr);
+                        rc = gmap_pte_op_fixup(parent, paddr, vmaddr, prot);
                         if (rc)
                                 return rc;
                         continue;
@@ -1910,10 +1913,12 @@ int gmap_shadow_page(struct gmap *sg, unsigned long saddr, pte_t pte)
         unsigned long vmaddr, paddr;
         spinlock_t *ptl;
         pte_t *sptep, *tptep;
+        int prot;
         int rc;
 
         BUG_ON(!gmap_is_shadow(sg));
         parent = sg->parent;
+        prot = (pte_val(pte) & _PAGE_PROTECT) ? PROT_READ : PROT_WRITE;
 
         rmap = kzalloc(sizeof(*rmap), GFP_KERNEL);
         if (!rmap)
@@ -1955,7 +1960,7 @@ int gmap_shadow_page(struct gmap *sg, unsigned long saddr, pte_t pte)
                 radix_tree_preload_end();
                 if (!rc)
                         break;
-                rc = gmap_pte_op_fixup(parent, paddr, vmaddr);
+                rc = gmap_pte_op_fixup(parent, paddr, vmaddr, prot);
                 if (rc)
                         break;
         }