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SubjectRe: [PATCH] kprobes: disable preempt for module_text_address()
Lai Jiangshan wrote:
> actually, calling __module_text_address() in __register_kprobe() is
> better after my fix applied. but I found that a line have exceed
> 80 characters, so I don't use __module_text_address().

I don't think that coding style is a good reason not to fix it...:(

Anyway, I think the issue that you pointed must be fixed.
I found there were same kind of issues in kprobes and updated
your patch. This includes fixes which Hiroshi pointed out.

Thanks a lot! :)

__register_kprobe() can be preempted after checking probing address
but before try_module_get() or module_put(), and in this interval the
module can be unloaded. In that case, try_module_get(probed_mod) or
module_put(mod) will access to invalid address, or kprobe will probe
invalid address.

this patch uses preempt_disable() to protect it and use
__module_text_address() and __kernel_text_address().

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
---
kernel/kprobes.c | 21 +++++++++++++++------
1 file changed, 15 insertions(+), 6 deletions(-)

Index: 2.6.28-rc3/kernel/kprobes.c
===================================================================
--- 2.6.28-rc3.orig/kernel/kprobes.c
+++ 2.6.28-rc3/kernel/kprobes.c
@@ -613,30 +613,37 @@ static int __kprobes __register_kprobe(s
return -EINVAL;
p->addr = addr;

- if (!kernel_text_address((unsigned long) p->addr) ||
- in_kprobes_functions((unsigned long) p->addr))
+ preempt_disable();
+ if (!__kernel_text_address((unsigned long) p->addr) ||
+ in_kprobes_functions((unsigned long) p->addr)) {
+ preempt_enable();
return -EINVAL;
+ }

p->mod_refcounted = 0;

/*
* Check if are we probing a module.
*/
- probed_mod = module_text_address((unsigned long) p->addr);
+ probed_mod = __module_text_address((unsigned long) p->addr);
if (probed_mod) {
- struct module *calling_mod = module_text_address(called_from);
+ struct module *calling_mod;
+ calling_mod = __module_text_address(called_from);
/*
* We must allow modules to probe themself and in this case
* avoid incrementing the module refcount, so as to allow
* unloading of self probing modules.
*/
if (calling_mod && calling_mod != probed_mod) {
- if (unlikely(!try_module_get(probed_mod)))
+ if (unlikely(!try_module_get(probed_mod))) {
+ preempt_enable();
return -EINVAL;
+ }
p->mod_refcounted = 1;
} else
probed_mod = NULL;
}
+ preempt_enable();

p->nmissed = 0;
INIT_LIST_HEAD(&p->list);
@@ -718,9 +725,11 @@ static void __kprobes __unregister_kprob
struct kprobe *old_p;

if (p->mod_refcounted) {
- mod = module_text_address((unsigned long)p->addr);
+ preempt_disable();
+ mod = __module_text_address((unsigned long)p->addr);
if (mod)
module_put(mod);
+ preempt_enable();
}

if (list_empty(&p->list) || list_is_singular(&p->list)) {

--
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com




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