xen-gntdev: Avoid double-mapping memory

If an already-mapped area of the device was mapped into userspace a
second time, a hypercall was incorrectly made to remap the memory
again. Avoid the hypercall on later mmap calls, and fail the mmap call
if a writable mapping is attempted on a read-only range.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 12 insertions, 3 deletions

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 4687cd557c97..2c4cc940c429 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -258,6 +258,9 @@ static int map_grant_pages(struct grant_map *map)
         phys_addr_t addr;
 
         if (!use_ptemod) {
+                /* Note: it could already be mapped */
+                if (map->map_ops[0].handle)
+                        return 0;
                 for (i = 0; i < map->count; i++) {
                         addr = (phys_addr_t)
                                 pfn_to_kaddr(page_to_pfn(map->pages[i]));
@@ -668,9 +671,15 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
         if (use_ptemod)
                 map->vma = vma;
 
-        map->flags = GNTMAP_host_map;
-        if (!(vma->vm_flags & VM_WRITE))
-                map->flags |= GNTMAP_readonly;
+        if (map->flags) {
+                if ((vma->vm_flags & VM_WRITE) &&
+                                (map->flags & GNTMAP_readonly))
+                        return -EINVAL;
+        } else {
+                map->flags = GNTMAP_host_map;
+                if (!(vma->vm_flags & VM_WRITE))
+                        map->flags |= GNTMAP_readonly;
+        }
 
         spin_unlock(&priv->lock);