From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CA0EDC43441 for ; Wed, 28 Nov 2018 14:20:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 99453208E7 for ; Wed, 28 Nov 2018 14:20:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 99453208E7 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728590AbeK2BW2 (ORCPT ); Wed, 28 Nov 2018 20:22:28 -0500 Received: from mx1.redhat.com ([209.132.183.28]:54856 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728387AbeK2BW2 (ORCPT ); Wed, 28 Nov 2018 20:22:28 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 55FB84D4DF; Wed, 28 Nov 2018 14:20:39 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.12]) by smtp.corp.redhat.com (Postfix) with SMTP id A88AC1057042; Wed, 28 Nov 2018 14:20:07 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 28 Nov 2018 15:20:39 +0100 (CET) Date: Wed, 28 Nov 2018 15:20:06 +0100 From: Oleg Nesterov To: "Dmitry V. Levin" Cc: Kees Cook , Jann Horn , Michael Ellerman , Elvira Khabirova , Eugene Syromyatnikov , Steven Rostedt , linux-kernel@vger.kernel.org, Andy Lutomirski , linux-api@vger.kernel.org, Ingo Molnar , strace-devel@lists.strace.io Subject: Re: [PATCH v4 1/2] ptrace: save the type of syscall-stop in ptrace_message Message-ID: <20181128142006.GE30395@redhat.com> References: <20181128130439.GB28206@altlinux.org> <20181128130601.GC28206@altlinux.org> <20181128134913.GC30395@redhat.com> <20181128140533.GF28206@altlinux.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181128140533.GF28206@altlinux.org> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Wed, 28 Nov 2018 14:20:39 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/28, Dmitry V. Levin wrote: > > On Wed, Nov 28, 2018 at 02:49:14PM +0100, Oleg Nesterov wrote: > > On 11/28, Dmitry V. Levin wrote: > > > > > > +/* > > > + * These values are stored in task->ptrace_message by tracehook_report_syscall_* > > > + * to describe current syscall-stop. > > > + * > > > + * Values for these constants are chosen so that they do not appear > > > + * in task->ptrace_message by other means. > > > + */ > > > +#define PTRACE_EVENTMSG_SYSCALL_ENTRY 0x80000000U > > > +#define PTRACE_EVENTMSG_SYSCALL_EXIT 0x90000000U > > > > Again, I do not really understand the comment... Why should we care about > > "do not appear in task->ptrace_message by other means" ? > > > > 2/2 should detect ptrace_report_syscall() case correctly, so we can use any > > numbers, say, 1 and 2? > > > > If debugger does PTRACE_GETEVENTMSG it should know how to interpet the value > > anyway after wait(status). > > Given that without this patch the value returned by PTRACE_GETEVENTMSG > during syscall stop is undefined, we need two different ptrace_message > values that cannot be set by other ptrace events to enable reliable > identification of syscall-enter-stop and syscall-exit-stop in userspace: > if we make PTRACE_GETEVENTMSG return 0 or any other value routinely set by > other ptrace events, it would be hard for userspace to find out whether > the kernel implements new semantics or not. Hmm, why? Debugger can just do ptrace(PTRACE_GET_SYSCALL_INFO, NULL), if it returns EIO then it is not implemented? Oleg.