MFC r315272, r315370

r315272:
Implement INHERIT_ZERO for minherit(2).

INHERIT_ZERO is an OpenBSD feature.

When a page is marked as such, it would be zeroed
upon fork().

This would be used in new arc4random(3) functions.

PR:	182610
Reviewed by:	kib (earlier version)
Differential Revision:	https://reviews.freebsd.org/D427

r315370:
The adj_free and max_free values of new_entry will be calculated and
assigned by subsequent vm_map_entry_link(), therefore, remove the
pointless copying.

Submitted by:	alc

2 files changed, 30 insertions, 0 deletions

diff --git a/sys/vm/vm.h b/sys/vm/vm.h
index 1df51fe..68bb4d1 100644
--- a/sys/vm/vm.h
+++ b/sys/vm/vm.h
@@ -68,6 +68,7 @@ typedef char vm_inherit_t;	/* inheritance codes */
 #define	VM_INHERIT_SHARE	((vm_inherit_t) 0)
 #define	VM_INHERIT_COPY		((vm_inherit_t) 1)
 #define	VM_INHERIT_NONE		((vm_inherit_t) 2)
+#define	VM_INHERIT_ZERO		((vm_inherit_t) 3)
 #define	VM_INHERIT_DEFAULT	VM_INHERIT_COPY
 
 typedef u_char vm_prot_t;	/* protection codes */
diff --git a/sys/vm/vm_map.c b/sys/vm/vm_map.c
index 2296fb1..2ef89bd 100644
--- a/sys/vm/vm_map.c
+++ b/sys/vm/vm_map.c
@@ -2294,6 +2294,7 @@ vm_map_inherit(vm_map_t map, vm_offset_t start, vm_offset_t end,
 	case VM_INHERIT_NONE:
 	case VM_INHERIT_COPY:
 	case VM_INHERIT_SHARE:
+	case VM_INHERIT_ZERO:
 		break;
 	default:
 		return (KERN_INVALID_ARGUMENT);
@@ -3452,6 +3453,34 @@ vmspace_fork(struct vmspace *vm1, vm_ooffset_t *fork_charge)
 			vm_map_copy_entry(old_map, new_map, old_entry,
 			    new_entry, fork_charge);
 			break;
+
+		case VM_INHERIT_ZERO:
+			/*
+			 * Create a new anonymous mapping entry modelled from
+			 * the old one.
+			 */
+			new_entry = vm_map_entry_create(new_map);
+			memset(new_entry, 0, sizeof(*new_entry));
+
+			new_entry->start = old_entry->start;
+			new_entry->end = old_entry->end;
+			new_entry->avail_ssize = old_entry->avail_ssize;
+			new_entry->eflags = old_entry->eflags &
+			    ~(MAP_ENTRY_USER_WIRED | MAP_ENTRY_IN_TRANSITION |
+			    MAP_ENTRY_VN_WRITECNT);
+			new_entry->protection = old_entry->protection;
+			new_entry->max_protection = old_entry->max_protection;
+			new_entry->inheritance = VM_INHERIT_ZERO;
+
+			vm_map_entry_link(new_map, new_map->header.prev,
+			    new_entry);
+			vmspace_map_entry_forked(vm1, vm2, new_entry);
+
+			new_entry->cred = curthread->td_ucred;
+			crhold(new_entry->cred);
+			*fork_charge += (new_entry->end - new_entry->start);
+
+			break;
 		}
 		old_entry = old_entry->next;
 	}