From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752788Ab3KEGJH (ORCPT ); Tue, 5 Nov 2013 01:09:07 -0500 Received: from mail-ea0-f178.google.com ([209.85.215.178]:45571 "EHLO mail-ea0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750774Ab3KEGJG (ORCPT ); Tue, 5 Nov 2013 01:09:06 -0500 Date: Tue, 5 Nov 2013 07:09:01 +0100 From: Ingo Molnar To: Steven Rostedt Cc: Masami Hiramatsu , 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: <20131105060901.GA29936@gmail.com> References: <20131101112530.14657.87835.stgit@kbuild-fedora.novalocal> <20131101112537.14657.88496.stgit@kbuild-fedora.novalocal> <20131104210053.76c37210@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20131104210053.76c37210@gandalf.local.home> 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 * 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. Thanks, Ingo