From: sf <sf@openbsd.org>
Date: Sat, 1 Jul 2017 19:38:41 +0000 (+0000)
Subject: Use absolute pointers in codepatch entries
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=2daa523994d9464fa02a5384e7a44ef5b457cf06;p=openbsd

Use absolute pointers in codepatch entries

Instead of offsets to KERNBASE, store absolute pointers in the
codepatch entries. This makes the resulting kernel a few KB larger on
amd64, but KERNBASE will go away when ASLR is introduced.

Requested by deraadt@
---

diff --git a/sys/arch/amd64/amd64/codepatch.c b/sys/arch/amd64/amd64/codepatch.c
index 41bd08fc906..323704415a7 100644
--- a/sys/arch/amd64/amd64/codepatch.c
+++ b/sys/arch/amd64/amd64/codepatch.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: codepatch.c,v 1.3 2017/03/26 23:27:44 jca Exp $    */
+/*      $OpenBSD: codepatch.c,v 1.4 2017/07/01 19:38:41 sf Exp $    */
 /*
  * Copyright (c) 2014-2015 Stefan Fritsch <sf@sfritsch.de>
  *
@@ -26,10 +26,12 @@
 #endif
 
 struct codepatch {
-	uint32_t offset;
+	vaddr_t addr;
 	uint16_t len;
 	uint16_t tag;
+	uint32_t _padding;
 };
+CTASSERT(sizeof(struct codepatch) % 8 == 0);
 
 extern struct codepatch codepatch_begin;
 extern struct codepatch codepatch_end;
@@ -104,7 +106,7 @@ codepatch_nop(uint16_t tag)
 {
 	struct codepatch *patch;
 	unsigned char *rwaddr;
-	vaddr_t addr, rwmap = 0;
+	vaddr_t rwmap = 0;
 	int i = 0;
 
 	DBGPRINT("patching tag %u", tag);
@@ -112,8 +114,7 @@ codepatch_nop(uint16_t tag)
 	for (patch = &codepatch_begin; patch < &codepatch_end; patch++) {
 		if (patch->tag != tag)
 			continue;
-		addr = KERNBASE + patch->offset;
-		rwaddr = codepatch_maprw(&rwmap, addr);
+		rwaddr = codepatch_maprw(&rwmap, patch->addr);
 		codepatch_fill_nop(rwaddr, patch->len);
 		i++;
 	}
@@ -127,7 +128,7 @@ codepatch_replace(uint16_t tag, void *code, size_t len)
 {
 	struct codepatch *patch;
 	unsigned char *rwaddr;
-	vaddr_t addr, rwmap = 0;
+	vaddr_t rwmap = 0;
 	int i = 0;
 
 	DBGPRINT("patching tag %u with %p", tag, code);
@@ -135,13 +136,12 @@ codepatch_replace(uint16_t tag, void *code, size_t len)
 	for (patch = &codepatch_begin; patch < &codepatch_end; patch++) {
 		if (patch->tag != tag)
 			continue;
-		addr = KERNBASE + patch->offset;
 
 		if (len > patch->len) {
 			panic("%s: can't replace len %u with %zu at %#lx",
-			    __func__, patch->len, len, addr);
+			    __func__, patch->len, len, patch->addr);
 		}
-		rwaddr = codepatch_maprw(&rwmap, addr);
+		rwaddr = codepatch_maprw(&rwmap, patch->addr);
 		memcpy(rwaddr, code, len);
 		codepatch_fill_nop(rwaddr + len, patch->len - len);
 		i++;
@@ -158,20 +158,19 @@ codepatch_call(uint16_t tag, void *func)
 	unsigned char *rwaddr;
 	int32_t offset;
 	int i = 0;
-	vaddr_t addr, rwmap = 0;
+	vaddr_t rwmap = 0;
 
 	DBGPRINT("patching tag %u with call %p", tag, func);
 
 	for (patch = &codepatch_begin; patch < &codepatch_end; patch++) {
 		if (patch->tag != tag)
 			continue;
-		addr = KERNBASE + patch->offset;
 		if (patch->len < 5)
 			panic("%s: can't replace len %u with call at %#lx",
-			    __func__, patch->len, addr);
+			    __func__, patch->len, patch->addr);
 
-		offset = (vaddr_t)func - (addr + 5);
-		rwaddr = codepatch_maprw(&rwmap, addr);
+		offset = (vaddr_t)func - (patch->addr + 5);
+		rwaddr = codepatch_maprw(&rwmap, patch->addr);
 		rwaddr[0] = 0xe8; /* call near */
 		memcpy(rwaddr + 1, &offset, sizeof(offset));
 		codepatch_fill_nop(rwaddr + 5, patch->len - 5);
diff --git a/sys/arch/amd64/include/codepatch.h b/sys/arch/amd64/include/codepatch.h
index 9a29b3aaf77..92cd2db51a2 100644
--- a/sys/arch/amd64/include/codepatch.h
+++ b/sys/arch/amd64/include/codepatch.h
@@ -1,4 +1,4 @@
-/*      $OpenBSD: codepatch.h,v 1.2 2015/04/19 19:45:21 sf Exp $    */
+/*      $OpenBSD: codepatch.h,v 1.3 2017/07/01 19:38:41 sf Exp $    */
 /*
  * Copyright (c) 2014-2015 Stefan Fritsch <sf@sfritsch.de>
  *
@@ -41,9 +41,10 @@ void codepatch_call(uint16_t tag, void *func);
 #define	CODEPATCH_END(tag)			 \
 	999:					 \
 	.section .codepatch, "a"		;\
-	.int (998b - KERNBASE)			;\
+	.quad 998b				;\
 	.short (999b - 998b)			;\
 	.short tag				;\
+	.int 0					;\
 	.previous
 
 #define CPTAG_STAC		1