Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754790Ab2KUOQL (ORCPT ); Wed, 21 Nov 2012 09:16:11 -0500 Received: from mx1.redhat.com ([209.132.183.28]:16764 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754675Ab2KUOQJ (ORCPT ); Wed, 21 Nov 2012 09:16:09 -0500 Date: Wed, 21 Nov 2012 15:16:27 +0100 From: Oleg Nesterov To: u3557@miso.sublimeip.com Cc: Steven Rostedt , Frederic Weisbecker , Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org Subject: Re: [PATCH] arch_check_bp_in_kernelspace: fix the range check Message-ID: <20121121141627.GB21030@redhat.com> References: <20121109182943.GA2789@redhat.com> <20121109183026.GA2719@redhat.com> <20121119174728.GA11365@redhat.com> <1353349500.6276.9.camel@gandalf.local.home> <20121120154824.GA17534@redhat.com> <20121120183243.GA31290@redhat.com> <3501c254c970c4dbd933022651622f79.squirrel@mail.sublimeip.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3501c254c970c4dbd933022651622f79.squirrel@mail.sublimeip.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1423 Lines: 53 Hi Amnon, Please read my previous email ;) http://marc.info/?l=linux-kernel&m=135342649119153 On 11/21, u3557@miso.sublimeip.com wrote: > > Hi Oleg, > > > Or. Perhaps we can define TRAP_VSYSCALL and change emulate_vsyscall() to > > do > > > > > > if (current->ptrace && test_thread_flag(TIF_SYSCALL_TRACE)) > > send_sigtrap(TRAP_VSYSCALL, ...); > > > > if it returns true? > > > > I wish it were possible, but the vsyscall page is entered in user-mode, Only in NATIVE mode. emulate_vsyscall() runs in kernel mode. And in the NATIVE mode PTRACE_SYSCALL should work just fine, because: > The vsyscall page was designed in order to avoid user/kernel context > switches, True, it was. But not today. Please look at __vsyscall_page: __vsyscall_page: mov $__NR_gettimeofday, %rax syscall ret If you want the "fast" sys_time() without entering the kernel, you can use __vdso_time(). And since vdso has the user-space mapping you can insert "int3" or use hw breakpoints. At least this is my understanding after I glanced at the new implementation. However. It is not that I think that TRAP_VSYSCALL is really good idea. At least it needs another option... Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/