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Message-ID: <5278D89B.1070806@hitachi.com>
Date: Tue, 05 Nov 2013 20:38:03 +0900
From: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Ananth N Mavinakayanahalli <ananth@...ibm.com>,
x86@...nel.org, lkml <linux-kernel@...r.kernel.org>,
Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>,
Andrew Morton <akpm@...ux-foundation.org>,
Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH -tip v2 3/3] [BUGFIX] kprobes: Prohibit probing on func_ptr_is_kernel_text
(2013/11/05 16:05), Ingo Molnar wrote:
>
> * Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:
>
>> (2013/11/05 15:09), Ingo Molnar wrote:
>>>
>>> * Steven Rostedt <rostedt@...dmis.org> wrote:
>>>
>>>> On Fri, 01 Nov 2013 11:25:37 +0000
>>>> Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:
>>>>
>>>>> Prohibit probing on func_ptr_is_kernel_text().
>>>>> Since the func_ptr_is_kernel_text() is called from
>>>>> notifier_call_chain() which is called from int3 handler,
>>>>> probing it may cause double int3 fault and kernel will
>>>>> reboot.
>>>>>
>>>>> This happenes when the kernel built with CONFIG_DEBUG_NOTIFIERS=y.
>>>>>
>>>>> Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
>>>>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>>>>> Cc: "Uwe Kleine-König" <u.kleine-koenig@...gutronix.de>
>>>>> Cc: Borislav Petkov <bp@...e.de>
>>>>> Cc: Ingo Molnar <mingo@...nel.org>
>>>>> ---
>>>>> kernel/extable.c | 2 +-
>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/kernel/extable.c b/kernel/extable.c
>>>>> index 832cb28..022fb25 100644
>>>>> --- a/kernel/extable.c
>>>>> +++ b/kernel/extable.c
>>>>> @@ -129,7 +129,7 @@ int kernel_text_address(unsigned long addr)
>>>>> * pointer is part of the kernel text, we need to do some
>>>>> * special dereferencing first.
>>>>> */
>>>>> -int func_ptr_is_kernel_text(void *ptr)
>>>>> +int nokprobe func_ptr_is_kernel_text(void *ptr)
>>>>> {
>>>>> unsigned long addr;
>>>>> addr = (unsigned long) dereference_function_descriptor(ptr);
>>>>>
>>>>
>>>> One thing I worry about the "nokprobe" annotation, is that it moves the
>>>> location of the function out of local. This function no exists in the
>>>> section with its users. Same with the debug functions in the other
>>>> patch.
>>>
>>> Well, it's a bit like noinline, that changes the position of the function
>>> as well. So it's not true that 'noxyz' attributes don't affect function
>>> placement - they often don't, but some do.
>>>
>>> The more important aspect is that 'noprobe' makes it really, really
>>> apparent what the tag is about, at first sight.
>>>
>>> _How_ the 'non probing' is achived is an implementational detail when
>>> kprobes are enabled: right now it puts a function into a separate section,
>>> but we could just a much build a list of function names and check against
>>> it at probe insertion time.
>>
>> Actually, kprobes already has it -- kprobes_blacklist. Currently the
>> list is manually maintained in kprobes.c separated from the function
>> definition. [...]
>
> Yes, I meant a list that is built automatically from the 'noprobe'
> annotations.
Agreed. That makes maintenance work simple, and we can remove
".kprobes.text" section.
>> [...] I hope to build the list when the kernel build time if possible...
>> Would you have any idea to classify some annotated(but no side-effect)
>> functions?
>
> The macro magic I can think of would need to change the syntax of the
> function definition - for example that is how the SYSCALL_DEFINE*() macros
> work.
Would you mean something like the below macro? :)
NOKPROBE_SYMBOL(int, func_ptr_is_kernel_text)(void *ptr)
which is expanded as;
static struct nokprobe_entry __used
__nokprobe_entry_func_ptr_is_kernel_text = {
.name = "func_ptr_is_kernel_text"
};
static struct kprobe_blacklist_entry __used
__attribute__((section("_nokprobe_list")))
__p_nokprobe_entry_func_ptr_is_kernel_text = &__nokprobe_entry_func_ptr_is_kernel_text;
int func_ptr_is_kernel_text(void *ptr)
Hmm, this looks worth to try.
Thank you,
--
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com
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