From: deraadt <deraadt@openbsd.org>
Date: Sat, 20 Jan 2024 13:19:37 +0000 (+0000)
Subject: Early during mimmutable(2) development, we had a big problem with the
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=38558285c928dfef552f8b65b2631f0a433f7b4c;p=openbsd

Early during mimmutable(2) development, we had a big problem with the
chrome v8_flags variable's placement in bss, and as a workaround made
it possible to demote a mimmutable mapping's permissions from RW to R.
Further mimmutable-related work in libc's malloc created the same
problem, which led to a better design: objects could be placed into
.openbsd.mutable region, and then at runtime their permission and
immutability could be manipulated better.  So the RW to R demotion
logic is no longer being used, and now this semantic is being deleted.
ok kettenis
---

diff --git a/lib/libc/sys/mimmutable.2 b/lib/libc/sys/mimmutable.2
index b97783559a7..03fff5cc747 100644
--- a/lib/libc/sys/mimmutable.2
+++ b/lib/libc/sys/mimmutable.2
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: mimmutable.2,v 1.3 2022/11/06 20:15:44 jmc Exp $
+.\"	$OpenBSD: mimmutable.2,v 1.4 2024/01/20 13:19:37 deraadt Exp $
 .\"
 .\" Copyright (c) 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -29,7 +29,7 @@
 .\"
 .\"	@(#)mimmutable.2	8.1 (Berkeley) 6/9/93
 .\"
-.Dd $Mdocdate: November 6 2022 $
+.Dd $Mdocdate: January 20 2024 $
 .Dt MIMMUTABLE 2
 .Os
 .Sh NAME
@@ -81,16 +81,3 @@ The
 .Fn mimmutable
 function first appeared in
 .Ox 7.3 .
-.Sh CAVEATS
-At present,
-.Xr mprotect 2
-may reduce permissions on immutable pages marked
-.Dv PROT_READ | PROT_WRITE
-to the less permissive
-.Dv PROT_READ .
-This one-way operation is permitted for an introductory period to observe how
-software uses this mechanism.
-It may change to require explicit mutable region annotation with
-.Va __attribute__((section(".openbsd.mutable")))
-and explicit calls to
-.Fn mimmutable .
diff --git a/sys/uvm/uvm_map.c b/sys/uvm/uvm_map.c
index 5164357733f..5078f3a229d 100644
--- a/sys/uvm/uvm_map.c
+++ b/sys/uvm/uvm_map.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: uvm_map.c,v 1.320 2024/01/16 19:05:01 deraadt Exp $	*/
+/*	$OpenBSD: uvm_map.c,v 1.321 2024/01/20 13:19:39 deraadt Exp $	*/
 /*	$NetBSD: uvm_map.c,v 1.86 2000/11/27 08:40:03 chs Exp $	*/
 
 /*
@@ -3144,16 +3144,9 @@ uvm_map_protect(struct vm_map *map, vaddr_t start, vaddr_t end,
 		if (iter->start == iter->end || UVM_ET_ISHOLE(iter))
 			continue;
 
-		if (checkimmutable &&
-		    (iter->etype & UVM_ET_IMMUTABLE)) {
-			if (iter->protection == (PROT_READ | PROT_WRITE) &&
-			    new_prot == PROT_READ) {
-				/* Permit RW to R as a data-locking mechanism */
-				;
-			} else {
-				error = EPERM;
-				goto out;
-			}
+		if (checkimmutable && (iter->etype & UVM_ET_IMMUTABLE)) {
+			error = EPERM;
+			goto out;
 		}
 		old_prot = iter->protection;
 		if (old_prot == PROT_NONE && new_prot != old_prot) {