slightly randomize the order that new pages populate their item lists in.

ok tedu@ deraadt@

diff --git a/sys/kern/subr_pool.c b/sys/kern/subr_pool.c
index cbcbffb..f1c0873 100644 (file)
--- a/sys/kern/subr_pool.c
+++ b/sys/kern/subr_pool.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: subr_pool.c,v 1.221 2018/01/18 18:08:51 bluhm Exp $   */
+/*     $OpenBSD: subr_pool.c,v 1.222 2018/02/06 22:35:32 dlg Exp $     */
 /*     $NetBSD: subr_pool.c,v 1.61 2001/09/26 07:14:56 chs Exp $       */
 
 /*-
@@ -917,6 +917,8 @@ pool_p_alloc(struct pool *pp, int flags, int *slowdown)
        struct pool_page_header *ph;
        struct pool_item *pi;
        caddr_t addr;
+       unsigned int order;
+       int o;
        int n;
 
        pl_assert_unlocked(pp, &pp->pr_lock);
@@ -951,10 +953,19 @@ pool_p_alloc(struct pool *pp, int flags, int *slowdown)
 #endif /* DIAGNOSTIC */
 
        n = pp->pr_itemsperpage;
+       o = 32;
        while (n--) {
                pi = (struct pool_item *)addr;
                pi->pi_magic = POOL_IMAGIC(ph, pi);
-               XSIMPLEQ_INSERT_TAIL(&ph->ph_items, pi, pi_list);
+
+               if (o == 32) {
+                       order = arc4random();
+                       o = 0;
+               }
+               if (ISSET(order, 1 << o++))
+                       XSIMPLEQ_INSERT_TAIL(&ph->ph_items, pi, pi_list);
+               else
+                       XSIMPLEQ_INSERT_HEAD(&ph->ph_items, pi, pi_list);
 
 #ifdef DIAGNOSTIC
                if (POOL_PHPOISON(ph))