(2013/11/05 20:38), Masami Hiramatsu wrote: > (2013/11/05 16:05), Ingo Molnar wrote: >> >> * Masami Hiramatsu <[email protected]> wrote: >> >>> (2013/11/05 15:09), Ingo Molnar wrote: >>>> >>>> * Steven Rostedt <[email protected]> wrote: >>>> >>>>> On Fri, 01 Nov 2013 11:25:37 +0000 >>>>> Masami Hiramatsu <[email protected]> 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 <[email protected]> >>>>>> Cc: Andrew Morton <[email protected]> >>>>>> Cc: "Uwe Kleine-König" <[email protected]> >>>>>> Cc: Borislav Petkov <[email protected]> >>>>>> Cc: Ingo Molnar <[email protected]> >>>>>> --- >>>>>> 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) >
By the way, this method can be done in C file, but not in asm file. And there are many sensitive entries in the entry_*.S. I think we have two options. (A) keep the kprobes.text(or nokprobe.text) section for such assembler parts. (B) Put a starter symbol and end symbol in such region and make a list of symbols between them in build time by using nm. Anyway, until removing all __kprobes from kernel, we can not remove the kprobes.text section. So, at the first step I just try to introduce above macro and apply it to only the symbols in kprobes_blacklist. After that, I'll try to classify the real unsafe entries and apply the new macro. Eventually, I think I can remove all __kprobes. Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: [email protected] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
