lkml.org 
[lkml]   [2008]   [Aug]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: PATCH] debug: add notifier chain debugging
On Mon, 25 Aug 2008 22:08:00 -0700
"Tony Luck" <tony.luck@intel.com> wrote:

> >> This breaks on ia64 (and pa-risc I think) where function pointers
> >> don't point directly at the code, they point to a {code,data}
> >> structure which is itself located in data space, not text space.
> >
> > is there a way to go to the actual address? I'm sure this is a bit
> > more common.... (like kallsyms!)
>
> See dereference_function_descriptor() in lib/vsprintf.c (where it will
> be clear that my memory was wrong and that PPC64 is the other
> architecture that needs this).
>

The patch below fixes this;
Ingo, please replace the patch with this one.


From: Arjan van de Ven <arjan@linux.intel.com>
Subject: [PATCH] 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>
Acked-by: Tony Luck <tony.luck@intel.com>
---
include/linux/kernel.h | 3 +++
kernel/extable.c | 16 ++++++++++++++++
kernel/notifier.c | 6 ++++++
lib/vsprintf.c | 2 +-
4 files changed, 26 insertions(+), 1 deletions(-)
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 2651f80..4e1366b 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 823be11..522277c 100644
--- a/kernel/notifier.c
+++ b/kernel/notifier.c
@@ -82,6 +82,12 @@ static int __kprobes notifier_call_chain(struct notifier_block **nl,

while (nb && nr_to_call) {
next_nb = rcu_dereference(nb->next);
+ if (!func_ptr_is_kernel_text(nb->notifier_call)) {
+ WARN(1, "Invalid notifier called!");
+ nb = next_nb;
+ continue;
+ }
+
ret = nb->notifier_call(nb, val, v);

if (nr_calls)
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;
--
1.5.5.1


\
 
 \ /
  Last update: 2008-08-26 18:25    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site