From 1b2439dbb703ae8d95a9ce7ece6b7800b80f41f0 Mon Sep 17 00:00:00 2001
From: Arjan van de Ven <arjan@linux.intel.com>
Date: Fri, 15 Aug 2008 15:29:38 -0700
Subject: debug: add notifier chain debugging

during some development we suspected a case where we left something
in a notifier chain that was from a module that was unloaded already...
and that sort of thing is rather hard to track down.

This patch adds a very simple sanity check (which isn't all that
expensive) to make sure the notifier we're about to call is
actually from either the kernel itself of from a still-loaded
module, avoiding a hard-to-chase-down crash.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 lib/Kconfig.debug | 10 ++++++++++
 1 file changed, 10 insertions(+)

(limited to 'lib')

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 8b5a7d304a5f..342858fbabbc 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -536,6 +536,16 @@ config DEBUG_SG
 
 	  If unsure, say N.
 
+config DEBUG_NOTIFIERS
+	bool "Debug notifier call chains"
+	depends on DEBUG_KERNEL
+	help
+	  Enable this to turn on sanity checking for notifier call chains.
+	  This is most useful for kernel developers to make sure that
+	  modules properly unregister themselves from notifier chains.
+	  This is a relatively cheap check but if you care about maximum
+	  performance, say N.
+
 config FRAME_POINTER
 	bool "Compile the kernel with frame pointers"
 	depends on DEBUG_KERNEL && \
-- 
cgit v1.2.3-70-g09d2


From ab7476cf76e560f0efda2a631a70aabe93009025 Mon Sep 17 00:00:00 2001
From: Arjan van de Ven <arjan@linux.intel.com>
Date: Fri, 15 Aug 2008 15:29:38 -0700
Subject: debug: add notifier chain debugging, v2

- unbreak ia64 (and powerpc) where function pointers dont
  point at code but at data (reported by Tony Luck)

[ mingo@elte.hu: various cleanups ]

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 include/linux/kernel.h |  3 +++
 kernel/extable.c       | 16 ++++++++++++++++
 kernel/notifier.c      | 10 +---------
 lib/vsprintf.c         |  2 +-
 4 files changed, 21 insertions(+), 10 deletions(-)

(limited to 'lib')

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 2651f805ba6d..4e1366b552ae 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -187,6 +187,9 @@ extern unsigned long long memparse(char *ptr, char **retptr);
 extern int core_kernel_text(unsigned long addr);
 extern int __kernel_text_address(unsigned long addr);
 extern int kernel_text_address(unsigned long addr);
+extern int func_ptr_is_kernel_text(void *ptr);
+extern void *dereference_function_descriptor(void *ptr);
+
 struct pid;
 extern struct pid *session_of_pgrp(struct pid *pgrp);
 
diff --git a/kernel/extable.c b/kernel/extable.c
index a26cb2e17023..adf0cc9c02d6 100644
--- a/kernel/extable.c
+++ b/kernel/extable.c
@@ -66,3 +66,19 @@ int kernel_text_address(unsigned long addr)
 		return 1;
 	return module_text_address(addr) != NULL;
 }
+
+/*
+ * On some architectures (PPC64, IA64) function pointers
+ * are actually only tokens to some data that then holds the
+ * real function address. As a result, to find if a function
+ * pointer is part of the kernel text, we need to do some
+ * special dereferencing first.
+ */
+int func_ptr_is_kernel_text(void *ptr)
+{
+	unsigned long addr;
+	addr = (unsigned long) dereference_function_descriptor(ptr);
+	if (core_kernel_text(addr))
+		return 1;
+	return module_text_address(addr) != NULL;
+}
diff --git a/kernel/notifier.c b/kernel/notifier.c
index 143fdd77dbf7..0f39e398ef60 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -21,10 +21,6 @@ BLOCKING_NOTIFIER_HEAD(reboot_notifier_list);
 static int notifier_chain_register(struct notifier_block **nl,
 		struct notifier_block *n)
 {
-	if (!kernel_text_address((unsigned long)n->notifier_call)) {
-		WARN(1, "Invalid notifier registered!");
-		return 0;
-	}
 	while ((*nl) != NULL) {
 		if (n->priority > (*nl)->priority)
 			break;
@@ -38,10 +34,6 @@ static int notifier_chain_register(struct notifier_block **nl,
 static int notifier_chain_cond_register(struct notifier_block **nl,
 		struct notifier_block *n)
 {
-	if (!kernel_text_address((unsigned long)n->notifier_call)) {
-		WARN(1, "Invalid notifier registered!");
-		return 0;
-	}
 	while ((*nl) != NULL) {
 		if ((*nl) == n)
 			return 0;
@@ -92,7 +84,7 @@ static int __kprobes notifier_call_chain(struct notifier_block **nl,
 		next_nb = rcu_dereference(nb->next);
 
 #ifdef CONFIG_DEBUG_NOTIFIERS
-		if (!kernel_text_address((unsigned long)nb->notifier_call)) {
+		if (unlikely(!func_ptr_is_kernel_text(nb->notifier_call))) {
 			WARN(1, "Invalid notifier called!");
 			nb = next_nb;
 			continue;
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index d8d1d1142248..f5e5ffb9942f 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -513,7 +513,7 @@ static char *string(char *buf, char *end, char *s, int field_width, int precisio
 	return buf;
 }
 
-static inline void *dereference_function_descriptor(void *ptr)
+void *dereference_function_descriptor(void *ptr)
 {
 #if defined(CONFIG_IA64) || defined(CONFIG_PPC64)
 	void *p;
-- 
cgit v1.2.3-70-g09d2