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, 6 insertions, 2 deletions

diff --git a/sys/arch/sh/sh/mem.c b/sys/arch/sh/sh/mem.c
index fdbe75a5b71..596864a52ca 100644
--- a/sys/arch/sh/sh/mem.c
+++ b/sys/arch/sh/sh/mem.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: mem.c,v 1.8 2016/08/16 18:21:54 tedu Exp $	*/
+/*	$OpenBSD: mem.c,v 1.9 2016/09/25 15:23:37 deraadt Exp $	*/
 /*	$NetBSD: mem.c,v 1.21 2006/07/23 22:06:07 ad Exp $	*/
 
 /*
@@ -101,16 +101,20 @@ cdev_decl(mm);
 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:
 	case 12:
 		break;
 	default:
 		return (ENXIO);
 	}
-
 	return (0);
 }