Messages in this thread Patch in this message | | | Date | Wed, 05 Nov 2008 16:40:16 -0500 | From | Masami Hiramatsu <> | Subject | Re: [PATCH] kprobes: disable preempt for module_text_address() |
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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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