xen/pvcalls: use alloc/free_pages_exact()

Instead of __get_free_pages() and free_pages() use alloc_pages_exact()
and free_pages_exact(). This is in preparation of a change of
gnttab_end_foreign_access() which will prohibit use of high-order
pages.

This is part of CVE-2022-23041 / XSA-396.

Reported-by: Simon Gaiser <simon@invisiblethingslab.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
V4:
- new patch

diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
index 3c9ae15..0ca351f 100644 (file)
--- a/drivers/xen/pvcalls-front.c
+++ b/drivers/xen/pvcalls-front.c
@@ -337,8 +337,8 @@ static void free_active_ring(struct sock_mapping *map)
        if (!map->active.ring)
                return;
 
-       free_pages((unsigned long)map->active.data.in,
-                       map->active.ring->ring_order);
+       free_pages_exact(map->active.data.in,
+                        PAGE_SIZE << map->active.ring->ring_order);
        free_page((unsigned long)map->active.ring);
 }
 
@@ -352,8 +352,8 @@ static int alloc_active_ring(struct sock_mapping *map)
                goto out;
 
        map->active.ring->ring_order = PVCALLS_RING_ORDER;
-       bytes = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
-                                       PVCALLS_RING_ORDER);
+       bytes = alloc_pages_exact(PAGE_SIZE << PVCALLS_RING_ORDER,
+                                 GFP_KERNEL | __GFP_ZERO);
        if (!bytes)
                goto out;