From 1a48cf1747c39cd90cef462c6d8ba0cb89a74473 Mon Sep 17 00:00:00 2001
From: kettenis <kettenis@openbsd.org>
Date: Thu, 19 Jan 2023 20:17:11 +0000
Subject: [PATCH] Revise implementation of pmap_protect(9) in preparation for
 execute-only support.  The current implementation doesn't handle the
 transition from RWX to RW correctly.  Also generalize the
 pmap_write_protect() function in recognition of the fact that execute
 permission, write permission, and in the future read permission on executable
 pages, are handled by separate bits.

ok deraadt@, mpi@
---
 sys/arch/amd64/amd64/pmap.c   | 14 ++++++++------
 sys/arch/amd64/include/pmap.h | 12 +++++-------
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/sys/arch/amd64/amd64/pmap.c b/sys/arch/amd64/amd64/pmap.c
index 893f840baf8..ea9b2c142e3 100644
--- a/sys/arch/amd64/amd64/pmap.c
+++ b/sys/arch/amd64/amd64/pmap.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: pmap.c,v 1.156 2022/11/29 21:41:39 guenther Exp $	*/
+/*	$OpenBSD: pmap.c,v 1.157 2023/01/19 20:17:11 kettenis Exp $	*/
 /*	$NetBSD: pmap.c,v 1.3 2003/05/08 18:13:13 thorpej Exp $	*/
 
 /*
@@ -2105,7 +2105,8 @@ pmap_clear_attrs(struct vm_page *pg, unsigned long clearbits)
 void
 pmap_write_protect(struct pmap *pmap, vaddr_t sva, vaddr_t eva, vm_prot_t prot)
 {
-	pt_entry_t nx, *spte, *epte;
+	pt_entry_t *spte, *epte;
+	pt_entry_t clear = 0, set = 0;
 	vaddr_t blockend;
 	int shootall = 0, shootself;
 	vaddr_t va;
@@ -2118,9 +2119,10 @@ pmap_write_protect(struct pmap *pmap, vaddr_t sva, vaddr_t eva, vm_prot_t prot)
 	sva &= PG_FRAME;
 	eva &= PG_FRAME;
 
-	nx = 0;
+	if (!(prot & PROT_WRITE))
+		clear = PG_RW;
 	if (!(prot & PROT_EXEC))
-		nx = pg_nx;
+		set |= pg_nx;
 
 	if ((eva - sva > 32 * PAGE_SIZE) && sva < VM_MIN_KERNEL_ADDRESS)
 		shootall = 1;
@@ -2158,8 +2160,8 @@ pmap_write_protect(struct pmap *pmap, vaddr_t sva, vaddr_t eva, vm_prot_t prot)
 		for (/*null */; spte < epte ; spte++) {
 			if (!pmap_valid_entry(*spte))
 				continue;
-			pmap_pte_clearbits(spte, PG_RW);
-			pmap_pte_setbits(spte, nx);
+			pmap_pte_clearbits(spte, clear);
+			pmap_pte_setbits(spte, set);
 		}
 	}
 
diff --git a/sys/arch/amd64/include/pmap.h b/sys/arch/amd64/include/pmap.h
index 4cfd83eb244..3660f440138 100644
--- a/sys/arch/amd64/include/pmap.h
+++ b/sys/arch/amd64/include/pmap.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: pmap.h,v 1.83 2023/01/17 19:29:09 kettenis Exp $	*/
+/*	$OpenBSD: pmap.h,v 1.84 2023/01/19 20:17:12 kettenis Exp $	*/
 /*	$NetBSD: pmap.h,v 1.1 2003/04/26 18:39:46 fvdl Exp $	*/
 
 /*
@@ -475,12 +475,10 @@ pmap_page_protect(struct vm_page *pg, vm_prot_t prot)
 static inline void
 pmap_protect(struct pmap *pmap, vaddr_t sva, vaddr_t eva, vm_prot_t prot)
 {
-	if ((prot & PROT_WRITE) == 0) {
-		if (prot & (PROT_READ| PROT_EXEC)) {
-			pmap_write_protect(pmap, sva, eva, prot);
-		} else {
-			pmap_remove(pmap, sva, eva);
-		}
+	if (prot != PROT_NONE) {
+		pmap_write_protect(pmap, sva, eva, prot);
+	} else {
+		pmap_remove(pmap, sva, eva);
 	}
 }
 
-- 
2.20.1