From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754168Ab3KEHFm (ORCPT ); Tue, 5 Nov 2013 02:05:42 -0500 Received: from mail-ea0-f182.google.com ([209.85.215.182]:54560 "EHLO mail-ea0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750759Ab3KEHFk (ORCPT ); Tue, 5 Nov 2013 02:05:40 -0500 Date: Tue, 5 Nov 2013 08:05:37 +0100 From: Ingo Molnar To: Masami Hiramatsu Cc: Steven Rostedt , Ananth N Mavinakayanahalli , x86@kernel.org, lkml , Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , Andrew Morton , Borislav Petkov Subject: Re: [PATCH -tip v2 3/3] [BUGFIX] kprobes: Prohibit probing on func_ptr_is_kernel_text Message-ID: <20131105070537.GA2007@gmail.com> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <5278973A.1010705@hitachi.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * 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. > [...] 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. It would be nice if there was a GCC extension that marked a function noinline and allowed the emitting of the function's address (and size) into a special section - but I'm not aware of any such compiler feature today. Thanks, Ingo