Messages in this thread Patch in this message |  | | | Date | Thu, 06 Nov 2008 10:37:48 -0500 | | From | Masami Hiramatsu <> | | Subject | [PATCH] kprobes: disable preempt for module_text_address() and kernel_text_address() |
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__register_kprobe() can be preempted after checking probing address but before module_text_address() or try_module_get(), and in this interval the module can be unloaded. In that case, try_module_get(probed_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> --- >> @@ -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(); > > this is bad fix, we have had a reference to mod. we don't need > preempt_disable() before module_put(mod).
Hmm, Indeed. So let's add a comment there.
kernel/kprobes.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 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); @@ -718,6 +725,10 @@ static void __kprobes __unregister_kprob struct kprobe *old_p;
if (p->mod_refcounted) { + /* + * Since we've already incremented refcount, + * we don't need to disable preemption. + */ mod = module_text_address((unsigned long)p->addr); if (mod) module_put(mod); -- Masami Hiramatsu
Software Engineer Hitachi Computer Products (America) Inc. Software Solutions Division
e-mail: mhiramat@redhat.com
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