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SubjectRe: [PATCH] kprobes: disable preempt for module_text_address()
Masami Hiramatsu wrote:
> 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) {

One question, off topic.
If calling_mod is NULL, no try_module_get(), is that OK?

thanks,
Hiroshi Shimamoto

> - 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)) {
>
>



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