[Xen-devel] [PATCH] xen-gntdev: Avoid double-mapping memory

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

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@xxxxxxxxxxxxx>
---
 drivers/xen/gntdev.c |   15 ++++++++++++---
 1 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 00e4644..e9d9180 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]));
@@ -674,9 +677,15 @@ 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);
 
-- 
1.7.3.4


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