From 2149600d129944f60cbc858bc669193af0523409 Mon Sep 17 00:00:00 2001
From: cinap_lenrek <cinap_lenrek@felloff.net>
Date: Tue, 27 Aug 2019 03:47:18 +0200
Subject: kernel: catch execution read fault on SG_NOEXEC segment

fault() now has an additional pc argument that is
used to detect fault on a non-executable segment.
that is, we check on read fault if the segment
has the SG_NOEXEC attribute and the program counter
is within faulting page.
---
 sys/src/9/port/fault.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

(limited to 'sys/src/9/port/fault.c')

diff --git a/sys/src/9/port/fault.c b/sys/src/9/port/fault.c
index f7732bbc3..4b6e12f67 100644
--- a/sys/src/9/port/fault.c
+++ b/sys/src/9/port/fault.c
@@ -142,7 +142,6 @@ done:
 static int
 fixfault(Segment *s, uintptr addr, int read)
 {
-	int type;
 	Pte **pte, *etp;
 	uintptr soff, mmuphys;
 	Page **pg, *old, *new;
@@ -159,8 +158,7 @@ fixfault(Segment *s, uintptr addr, int read)
 	if(pg > etp->last)
 		etp->last = pg;
 
-	type = s->type & SG_TYPE;
-	switch(type) {
+	switch(s->type & SG_TYPE) {
 	default:
 		panic("fault");
 		return -1;
@@ -221,6 +219,12 @@ fixfault(Segment *s, uintptr addr, int read)
 		(*pg)->modref = PG_MOD|PG_REF;
 		break;
 	}
+
+#ifdef PTENOEXEC
+	if((s->type & SG_NOEXEC) != 0)
+		mmuphys |= PTENOEXEC;
+#endif
+
 	qunlock(s);
 
 	putmmu(addr, mmuphys, *pg);
@@ -246,12 +250,12 @@ mapphys(Segment *s, uintptr addr, int attr)
 		mmuphys |= PTERONLY;
 
 #ifdef PTENOEXEC
-	if((attr & SG_NOEXEC) == SG_NOEXEC)
+	if((attr & SG_NOEXEC) != 0)
 		mmuphys |= PTENOEXEC;
 #endif
 
 #ifdef PTEDEVICE
-	if((attr & SG_DEVICE) == SG_DEVICE)
+	if((attr & SG_DEVICE) != 0)
 		mmuphys |= PTEDEVICE;
 	else
 #endif
@@ -266,7 +270,7 @@ mapphys(Segment *s, uintptr addr, int attr)
 }
 
 int
-fault(uintptr addr, int read)
+fault(uintptr addr, uintptr pc, int read)
 {
 	Segment *s;
 	char *sps;
@@ -298,7 +302,9 @@ fault(uintptr addr, int read)
 		if((attr & SG_TYPE) == SG_PHYSICAL)
 			attr |= s->pseg->attr;
 
-		if((attr & SG_FAULT) != 0 || !read && (attr & SG_RONLY) != 0) {
+		if((attr & SG_FAULT) != 0
+		|| read? (attr & SG_NOEXEC) != 0 && (addr & -BY2PG) == (pc & -BY2PG):
+			 (attr & SG_RONLY) != 0) {
 			qunlock(s);
 			up->psstate = sps;
 			if(up->kp && up->nerrlab)	/* for segio */
-- 
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