Add a sysctl to option USER_LDT, to control its behaviour, which will be

disabled by default.

Enable with sysctl -w machdep.userldt=1

This will allow people to use the few ports that require this functionality
to work without requiring the user to recompile a kernel.

The option USER_LDT remains in order to not increase size on the
installation media. It is now enabled in GENERIC.

Per espie@'s idea, but my diff was much simpler than his; ok deraadt@

6 files changed, 37 insertions, 11 deletions

diff --git a/sys/arch/i386/conf/GENERIC b/sys/arch/i386/conf/GENERIC
index 591351f0207..5eb63404036 100644
--- a/sys/arch/i386/conf/GENERIC
+++ b/sys/arch/i386/conf/GENERIC
@@ -1,4 +1,4 @@
-#	$OpenBSD: GENERIC,v 1.331 2003/03/09 01:54:20 tedu Exp $
+#	$OpenBSD: GENERIC,v 1.332 2003/03/28 00:49:13 miod Exp $
 #	$NetBSD: GENERIC,v 1.48 1996/05/20 18:17:23 mrg Exp $
 #
 #	GENERIC -- everything that's currently supported
@@ -17,7 +17,7 @@ option		GPL_MATH_EMULATE	# floating point emulation.
 option		USER_PCICONF	# user-space PCI configuration
 
 #option		VM86		# Virtual 8086 emulation
-#option		USER_LDT	# user-settable LDT; see i386_set_ldt(2)
+option		USER_LDT	# user-settable LDT; see i386_set_ldt(2)
 option		APERTURE	# in-kernel aperture driver for XFree86
 
 #option		KGDB		# Remote debugger support; exclusive of DDB
diff --git a/sys/arch/i386/i386/linux_machdep.c b/sys/arch/i386/i386/linux_machdep.c
index 8d580b53ec1..fd8dd6dc4c9 100644
--- a/sys/arch/i386/i386/linux_machdep.c
+++ b/sys/arch/i386/i386/linux_machdep.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: linux_machdep.c,v 1.24 2003/01/09 22:27:09 miod Exp $	*/
+/*	$OpenBSD: linux_machdep.c,v 1.25 2003/03/28 00:49:13 miod Exp $	*/
 /*	$NetBSD: linux_machdep.c,v 1.29 1996/05/03 19:42:11 christos Exp $	*/
 
 /*
@@ -295,6 +295,9 @@ linux_read_ldt(p, uap, retval)
 	caddr_t sg;
 	char *parms;
 
+	if (user_ldt_enable == 0)
+		return (ENOSYS);
+
 	sg = stackgap_init(p->p_emul);
 
 	gl.start = 0;
@@ -341,6 +344,9 @@ linux_write_ldt(p, uap, retval)
 	caddr_t sg;
 	char *parms;
 
+	if (user_ldt_enable == 0)
+		return (ENOSYS);
+
 	if (SCARG(uap, bytecount) != sizeof(ldt_info))
 		return (EINVAL);
 	if ((error = copyin(SCARG(uap, ptr), &ldt_info, sizeof(ldt_info))) != 0)
diff --git a/sys/arch/i386/i386/machdep.c b/sys/arch/i386/i386/machdep.c
index f52c4133b5d..473c2e4c8ad 100644
--- a/sys/arch/i386/i386/machdep.c
+++ b/sys/arch/i386/i386/machdep.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: machdep.c,v 1.223 2003/03/28 00:28:22 weingart Exp $	*/
+/*	$OpenBSD: machdep.c,v 1.224 2003/03/28 00:49:13 miod Exp $	*/
 /*	$NetBSD: machdep.c,v 1.214 1996/11/10 03:16:17 thorpej Exp $	*/
 
 /*-
@@ -196,6 +196,10 @@ char machine_arch[] = "i386";		/* machine == machine_arch */
 int	cpu_apmhalt = 0;	/* sysctl'd to 1 for halt -p hack */
 #endif
 
+#ifdef USER_LDT
+int	user_ldt_enable = 0;	/* sysctl'd to 1 to enable */
+#endif
+
 #ifdef	NBUF
 int	nbuf = NBUF;
 #else
@@ -2621,6 +2625,11 @@ cpu_sysctl(name, namelen, oldp, oldlenp, newp, newlen, p)
 		else
 			return (sysctl_int(oldp, oldlenp, newp, newlen, 
 			    &kbd_reset));
+#ifdef USER_LDT
+	case CPU_USERLDT:
+		return (sysctl_int(oldp, oldlenp, newp, newlen,
+		    &user_ldt_enable));
+#endif
 	default:
 		return EOPNOTSUPP;
 	}
diff --git a/sys/arch/i386/i386/svr4_machdep.c b/sys/arch/i386/i386/svr4_machdep.c
index a0569208045..cd36a59e9e7 100644
--- a/sys/arch/i386/i386/svr4_machdep.c
+++ b/sys/arch/i386/i386/svr4_machdep.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: svr4_machdep.c,v 1.16 2002/07/20 19:24:56 art Exp $	*/
+/*	$OpenBSD: svr4_machdep.c,v 1.17 2003/03/28 00:49:13 miod Exp $	*/
 /*	$NetBSD: svr4_machdep.c,v 1.24 1996/05/03 19:42:26 christos Exp $	 */
 
 /*
@@ -407,7 +407,9 @@ svr4_sys_sysarch(p, v, retval)
 
 	case SVR4_SYSARCH_DSCR:
 #ifdef USER_LDT
-		{
+		if (user_ldt_enable == 0)
+			return (ENOSYS);
+		else {
 			struct i386_set_ldt_args sa, *sap;
 			struct sys_sysarch_args ua;
 
diff --git a/sys/arch/i386/i386/sys_machdep.c b/sys/arch/i386/i386/sys_machdep.c
index ee8f3ab8e0e..dc6f71f384a 100644
--- a/sys/arch/i386/i386/sys_machdep.c
+++ b/sys/arch/i386/i386/sys_machdep.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: sys_machdep.c,v 1.19 2002/08/02 00:19:18 nate Exp $	*/
+/*	$OpenBSD: sys_machdep.c,v 1.20 2003/03/28 00:49:13 miod Exp $	*/
 /*	$NetBSD: sys_machdep.c,v 1.28 1996/05/03 19:42:29 christos Exp $	*/
 
 /*-
@@ -111,6 +111,9 @@ i386_get_ldt(p, args, retval)
 	union descriptor *lp;
 	struct i386_get_ldt_args ua;
 
+	if (user_ldt_enable == 0)
+		return (ENOSYS);
+
 	if ((error = copyin(args, &ua, sizeof(ua))) != 0)
 		return (error);
 
@@ -157,6 +160,9 @@ i386_set_ldt(p, args, retval)
 	struct i386_set_ldt_args ua;
 	union descriptor desc;
 
+	if (user_ldt_enable == 0)
+		return (ENOSYS);
+
 	if ((error = copyin(args, &ua, sizeof(ua))) != 0)
 		return (error);
 
@@ -195,10 +201,10 @@ i386_set_ldt(p, args, retval)
 		bzero((caddr_t)new_ldt + old_len, new_len - old_len);
 		pmap->pm_ldt = new_ldt;
 
-		if (pmap->pm_flags & PCB_USER_LDT)
+		if (pmap->pm_flags & PMF_USER_LDT)
 			ldt_free(pmap);
 		else
-			pmap->pm_flags |= PCB_USER_LDT;
+			pmap->pm_flags |= PMF_USER_LDT;
 		ldt_alloc(pmap, new_ldt, new_len);
 		pcb->pcb_ldt_sel = pmap->pm_ldt_sel;
 		if (pcb == curpcb)
diff --git a/sys/arch/i386/include/cpu.h b/sys/arch/i386/include/cpu.h
index 373902d18ed..20d694e7e24 100644
--- a/sys/arch/i386/include/cpu.h
+++ b/sys/arch/i386/include/cpu.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: cpu.h,v 1.45 2003/01/16 04:16:00 art Exp $	*/
+/*	$OpenBSD: cpu.h,v 1.46 2003/03/28 00:49:13 miod Exp $	*/
 /*	$NetBSD: cpu.h,v 1.35 1996/05/05 19:29:26 christos Exp $	*/
 
 /*-
@@ -197,6 +197,7 @@ int	math_emulate(struct trapframe *);
 
 #ifdef USER_LDT
 /* sys_machdep.h */
+extern int user_ldt_enable;
 void	i386_user_cleanup(struct pcb *);
 int	i386_get_ldt(struct proc *, void *, register_t *);
 int	i386_set_ldt(struct proc *, void *, register_t *);
@@ -238,7 +239,8 @@ void	setconf(void);
 #define CPU_APMWARN		9	/* APM battery warning percentage */
 #define CPU_KBDRESET		10	/* keyboard reset under pcvt */
 #define CPU_APMHALT		11	/* halt -p hack */
-#define	CPU_MAXID		12	/* number of valid machdep ids */
+#define CPU_USERLDT		12
+#define	CPU_MAXID		13	/* number of valid machdep ids */
 
 #define	CTL_MACHDEP_NAMES { \
 	{ 0, 0 }, \
@@ -253,6 +255,7 @@ void	setconf(void);
 	{ "apmwarn", CTLTYPE_INT }, \
 	{ "kbdreset", CTLTYPE_INT }, \
 	{ "apmhalt", CTLTYPE_INT }, \
+	{ "userldt", CTLTYPE_INT }, \
 }
 
 #endif /* !_I386_CPU_H_ */