[PATCH] debug: add notifier chain debugging, v2

From: Arjan van de Ven
Date: Fri Aug 15 2008 - 18:29:38 EST


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

[ mingo@xxxxxxx: various cleanups ]

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

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 1ceafa4..892529d 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 a26cb2e..adf0cc9 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 143fdd7..0f39e39 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 d8d1d11..f5e5ffb 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;
--
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