Index: machdep.c =================================================================== --- machdep.c (revision 274382) +++ machdep.c (working copy) @@ -3858,7 +3858,8 @@ set_mcontext(struct thread *td, const mcontext_t * int eflags, ret; tp = td->td_frame; - if (mcp->mc_len != sizeof(*mcp)) + if (mcp->mc_len != sizeof(*mcp) || + (mcp->mc_flags & ~_MC_FLAG_MASK) != 0) return (EINVAL); eflags = (mcp->mc_eflags & PSL_USERCHANGE) | (tp->tf_eflags & ~PSL_USERCHANGE);