dda500d0d8
This blocks an easy exploit of kernel bugs leading to dereference of a NULL pointer on some architectures (eg i386). The check can be disabled in various ways: -by CPP definitions in machine/types.h (portmaster's choice) -by a kernel config option USER_VA0_DISABLED_DEFAULT=0 -at runtime by sysctl vm.user_va0_disabled (cannot be cleared at securelevel>0)