From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754832Ab3KELiO (ORCPT ); Tue, 5 Nov 2013 06:38:14 -0500 Received: from mail9.hitachi.co.jp ([133.145.228.44]:57464 "EHLO mail9.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754815Ab3KELiK (ORCPT ); Tue, 5 Nov 2013 06:38:10 -0500 Message-ID: <5278D89B.1070806@hitachi.com> Date: Tue, 05 Nov 2013 20:38:03 +0900 From: Masami Hiramatsu Organization: Hitachi, Ltd., Japan User-Agent: Mozilla/5.0 (Windows NT 5.2; rv:13.0) Gecko/20120614 Thunderbird/13.0.1 MIME-Version: 1.0 To: Ingo Molnar Cc: Steven Rostedt , Ananth N Mavinakayanahalli , x86@kernel.org, lkml , =?UTF-8?B?VXdlIEtsZQ==?= =?UTF-8?B?aW5lLUvDtm5pZw==?= , Andrew Morton , Borislav Petkov Subject: Re: [PATCH -tip v2 3/3] [BUGFIX] kprobes: Prohibit probing on func_ptr_is_kernel_text References: <20131101112530.14657.87835.stgit@kbuild-fedora.novalocal> <20131101112537.14657.88496.stgit@kbuild-fedora.novalocal> <20131104210053.76c37210@gandalf.local.home> <20131105060901.GA29936@gmail.com> <5278973A.1010705@hitachi.com> <20131105070537.GA2007@gmail.com> In-Reply-To: <20131105070537.GA2007@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (2013/11/05 16:05), Ingo Molnar wrote: > > * Masami Hiramatsu wrote: > >> (2013/11/05 15:09), Ingo Molnar wrote: >>> >>> * Steven Rostedt wrote: >>> >>>> On Fri, 01 Nov 2013 11:25:37 +0000 >>>> Masami Hiramatsu 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 >>>>> Cc: Andrew Morton >>>>> Cc: "Uwe Kleine-König" >>>>> Cc: Borislav Petkov >>>>> Cc: Ingo Molnar >>>>> --- >>>>> 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@hitachi.com