Make a move towards ending 4 decades of kernel snooping.

Add sysctl kern.allowkmem (default 0) which controls the ability to open
/dev/mem or /dev/kmem at securelevel > 0.  Over 15 years we converted 99%
of utilities in the tree to operate on sysctl-nodes (either by themselves
or via code hiding in the guts of -lkvm).

pstat -d and -v & procmap are affected and continued use of them will
require kern.allowkmem=1 in /etc/sysctl.conf.  acpidump (and it's
buddy sendbug) are affected, but we'll work out a solution soon.

There will be some impact in ports.

ok kettenis guenther

1 files changed, 10 insertions, 5 deletions

diff --git a/sys/arch/alpha/alpha/mem.c b/sys/arch/alpha/alpha/mem.c
index ad3812ae22c..9a971403c36 100644
--- a/sys/arch/alpha/alpha/mem.c
+++ b/sys/arch/alpha/alpha/mem.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: mem.c,v 1.30 2016/08/15 22:01:59 tedu Exp $ */
+/* $OpenBSD: mem.c,v 1.31 2016/09/25 15:23:36 deraadt Exp $ */
 /* $NetBSD: mem.c,v 1.26 2000/03/29 03:48:20 simonb Exp $ */
 
 /*
@@ -70,12 +70,18 @@ extern int allowaperture;
 int
 mmopen(dev_t dev, int flag, int mode, struct proc *p)
 {
+	extern int allowkmem;
 
 	switch (minor(dev)) {
 	case 0:
 	case 1:
+		if (securelevel <= 0 || allowkmem)
+			break;
+		return (EPERM);
+	}
 	case 2:
-		return (0);
+	case 12:
+		break;
 #ifdef APERTURE
 	case 4:
 	        if (suser(p, 0) != 0 || !allowaperture)
@@ -86,13 +92,12 @@ mmopen(dev_t dev, int flag, int mode, struct proc *p)
 		if (ap_open_count > 0 && allowaperture < 3)
 			return (EPERM);
 		ap_open_count++;
-		return (0);
+		break;
 #endif
-	case 12:
-		return (0);
 	default:
 		return (ENXIO);
 	}
+	return (0);
 }
 
 int