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Fixed a shadow object search logic error.

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R/W shadow objects must be made read-only during a fork.
When searching for a writeable shadow object, it can only be the first
object on the vma object chain, therefore not traversing the object
chain and checking only the first object is sufficient.
This commit is contained in:
Bahadir Balban
2008-08-27 14:08:32 +03:00
parent 1ca3fce49b
commit f1b3a9b95d
1 changed files with 29 additions and 24 deletions
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53
tasks/mm0/src/fault.c
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@@ -503,7 +503,7 @@ out_success:
/*
* Sets all r/w shadow objects as read-only for the process
* so that as expected after a fork() operation, writes to those
* objects cause copy-on-write incidents.
* objects cause copy-on-write events.
*/
int vm_freeze_shadows(struct tcb *task)
{
@@ -520,34 +520,39 @@ int vm_freeze_shadows(struct tcb *task)
continue;
/* Get the first object */
while ((vmo_link = vma_next_link(&vma->vm_obj_list,
&vma->vm_obj_list))) {
vmo = vmo_link->obj;
BUG_ON(list_empty(&vma->vm_obj_list));
vmo_link = list_entry(vma->vm_obj_list.next,
struct vm_obj_link, list);
vmo = vmo_link->obj;
/* Is this a writeable shadow? */
if ((vmo->flags & VM_OBJ_SHADOW) &&
(vmo->flags & VM_WRITE)) {
/*
* Is this a writeable shadow?
*
* The only R/W shadow in a vma object chain
* can be the first one, so we don't check further
* objects if first one is not what we want.
*/
if (!((vmo->flags & VM_OBJ_SHADOW) &&
(vmo->flags & VM_WRITE)))
continue;
/* Make the object read only */
vmo->flags &= ~VM_WRITE;
vmo->flags |= VM_READ;
/* Make the object read only */
vmo->flags &= ~VM_WRITE;
vmo->flags |= VM_READ;
/*
* Make all pages on it read-only
* in the page tables.
*/
list_for_each_entry(p, &vmo->page_cache, list) {
/*
* Make all pages on it read-only
* in the page tables.
*/
list_for_each_entry(p, &vmo->page_cache, list) {
/* Find virtual address of each page */
virtual = vma_page_to_virtual(vma, p);
/* Find virtual address of each page */
virtual = vma_page_to_virtual(vma, p);
/* Map the page as read-only */
l4_map((void *)page_to_phys(p),
(void *)virtual, 1,
MAP_USR_RO_FLAGS, task->tid);
}
break;
}
/* Map the page as read-only */
l4_map((void *)page_to_phys(p),
(void *)virtual, 1,
MAP_USR_RO_FLAGS, task->tid);
}
}