untrusted comment: signature from openbsd 5.9 base secret key
RWQJVNompF3pwTe7dOmOWMBWXdhiISZOviqukj22AGzB2QbNtvWN6YisOdPi0bX5ouCzQh72fL8c/womXb1bQkhHV341qqZHyQE=

OpenBSD 5.9 errata 16, Jul 14, 2016:

The mmap extension __MAP_NOFAULT could overcommit resources and crash
the system.

Apply by doing:
   signify -Vep /etc/signify/openbsd-59-base.pub -x 016_mmap.patch.sig \
       -m - | (cd /usr/src && patch -p0)

And then rebuild and install a kernel:
   cd /usr/src/sys/arch/`machine`/conf
   KK=`sysctl -n kern.osversion | cut -d# -f1`
   config $KK
   cd ../compile/$KK
   make
   make install

Index: sys/uvm/uvm_mmap.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_mmap.c,v
retrieving revision 1.122
diff -u -p -r1.122 uvm_mmap.c
--- sys/uvm/uvm_mmap.c  11 Nov 2015 15:59:33 -0000      1.122
+++ sys/uvm/uvm_mmap.c  14 Jul 2016 03:10:40 -0000
@@ -491,7 +491,7 @@ sys_mmap(struct proc *p, void *v, regist
                       /* MAP_PRIVATE mappings can always write to */
                       maxprot |= PROT_WRITE;
               }
-               if ((flags & MAP_ANON) != 0 ||
+               if ((flags & MAP_ANON) != 0 || (flags & __MAP_NOFAULT) != 0 ||
                   ((flags & MAP_PRIVATE) != 0 && (prot & PROT_WRITE) != 0)) {
                       if (size >
                           (p->p_rlimit[RLIMIT_DATA].rlim_cur - ptoa(p->p_vmspace->vm_dused))) {
@@ -510,7 +510,7 @@ sys_mmap(struct proc *p, void *v, regist

is_anon:       /* label for SunOS style /dev/zero */

-               if ((flags & MAP_ANON) != 0 ||
+               if ((flags & MAP_ANON) != 0 || (flags & __MAP_NOFAULT) != 0 ||
                   ((flags & MAP_PRIVATE) != 0 && (prot & PROT_WRITE) != 0)) {
                       if (size >
                           (p->p_rlimit[RLIMIT_DATA].rlim_cur - ptoa(p->p_vmspace->vm_dused))) {