Index: sys/kern/sys_ptrace_common.c
===================================================================
RCS file: /cvsroot/src/sys/kern/sys_ptrace_common.c,v
retrieving revision 1.65
diff -u -r1.65 sys_ptrace_common.c
--- sys/kern/sys_ptrace_common.c	8 Oct 2019 12:29:57 -0000	1.65
+++ sys/kern/sys_ptrace_common.c	9 Oct 2019 12:53:30 -0000
@@ -286,6 +286,7 @@
 	case PT_DUMPCORE:
 	case PT_RESUME:
 	case PT_SUSPEND:
+	case PT_STOP:
 		result = KAUTH_RESULT_ALLOW;
 		break;
 
@@ -493,6 +494,7 @@
 	case PT_GET_PROCESS_STATE:
 	case PT_RESUME:
 	case PT_SUSPEND:
+	case PT_STOP:
 		/*
 		 * You can't do what you want to the process if:
 		 *	(1) It's not being traced at all,
@@ -511,8 +513,11 @@
 
 		/*
 		 *	(3) it's not currently stopped.
+		 *
+		 *	As an exception allow PT_KILL and PT_STOP here.
 		 */
-		if (t->p_stat != SSTOP || !t->p_waited /* XXXSMP */) {
+		if (req != PT_KILL && req != PT_STOP &&
+		    (t->p_stat != SSTOP || !t->p_waited /* XXXSMP */)) {
 			DPRINTF(("stat %d flag %d\n", t->p_stat,
 			    !t->p_waited));
 			return EBUSY;
@@ -540,6 +545,7 @@
 	case PT_TRACE_ME:
 	case PT_GET_SIGINFO:
 	case PT_SET_SIGINFO:
+	case PT_STOP:
 		return 1;
 	default:
 		return 0;
@@ -891,7 +897,7 @@
 #endif
 
 static int
-ptrace_sendsig(struct proc *t, struct lwp *lt, int signo, int resume_all)
+ptrace_sendsig(struct lwp *l, int req, struct proc *t, struct lwp *lt, int signo, int resume_all)
 {
 	ksiginfo_t ksi;
 
@@ -919,23 +925,20 @@
 		return 0;
 	}
 
-	KSI_INIT_EMPTY(&ksi);
-	if (t->p_sigctx.ps_faked) {
-		if (signo != t->p_sigctx.ps_info._signo)
-			return EINVAL;
-		t->p_sigctx.ps_faked = false;
-		ksi.ksi_info = t->p_sigctx.ps_info;
-		ksi.ksi_lid = t->p_sigctx.ps_lwp;
-	} else if (signo == 0) {
-		return 0;
-	} else {
-		ksi.ksi_signo = signo;
-	}
+	KASSERT(req == PT_KILL || req == PT_STOP || req == PT_ATTACH);
+
+	KSI_INIT(&ksi);
+	ksi.ksi_signo = signo;
+	ksi.ksi_code = SI_USER;
+	ksi.ksi_pid = l->l_proc->p_pid;
+	ksi.ksi_uid = kauth_cred_geteuid(l->l_cred);
+
+	t->p_sigctx.ps_faked = false;
+
 	DPRINTF(("%s: pid=%d.%d signal=%d resume_all=%d\n", __func__, t->p_pid,
-	    t->p_sigctx.ps_lwp, signo, resume_all));
+	    lt->l_lid, signo, resume_all));
 
-	kpsignal2(t, &ksi);
-	return 0;
+	return kpsignal2(t, &ksi);
 }
 
 static int
@@ -1328,7 +1331,7 @@
 			CLR(lt->l_pflag, LP_SINGLESTEP);
 		}
 	sendsig:
-		error = ptrace_sendsig(t, lt, signo, resume_all);
+		error = ptrace_sendsig(l, req, t, lt, signo, resume_all);
 		break;
 
 	case PT_SYSCALLEMU:
@@ -1361,6 +1364,11 @@
 		signo = SIGKILL;
 		goto sendsig;	/* in PT_CONTINUE, above. */
 
+	case PT_STOP:
+		/* just send the process a STOP signal. */
+		signo = SIGSTOP;
+		goto sendsig;	/* in PT_CONTINUE, above. */
+
 	case PT_ATTACH:
 		/*
 		 * Go ahead and set the trace flag.
Index: sys/sys/ptrace.h
===================================================================
RCS file: /cvsroot/src/sys/sys/ptrace.h,v
retrieving revision 1.65
diff -u -r1.65 ptrace.h
--- sys/sys/ptrace.h	11 Jun 2019 23:18:55 -0000	1.65
+++ sys/sys/ptrace.h	9 Oct 2019 12:53:30 -0000
@@ -57,6 +57,7 @@
 #define	PT_GET_SIGINFO		20	/* get signal state, defined below */
 #define	PT_RESUME		21	/* allow execution of the LWP */
 #define	PT_SUSPEND		22	/* prevent execution of the LWP */
+#define	PT_STOP			23	/* stop the child process */
 
 #define	PT_FIRSTMACH		32	/* for machine-specific requests */
 #include <machine/ptrace.h>		/* machine-specific requests, if any */