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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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