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 2E08EC0044C for ; Wed, 7 Nov 2018 16:44:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F0F942086C for ; Wed, 7 Nov 2018 16:44:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F0F942086C 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 S1731393AbeKHCQA (ORCPT ); Wed, 7 Nov 2018 21:16:00 -0500 Received: from mx1.redhat.com ([209.132.183.28]:39672 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727627AbeKHCQA (ORCPT ); Wed, 7 Nov 2018 21:16:00 -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 250054E33B; Wed, 7 Nov 2018 16:44:52 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.205.86]) by smtp.corp.redhat.com (Postfix) with SMTP id B1ABD105704E; Wed, 7 Nov 2018 16:44:45 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 7 Nov 2018 17:44:51 +0100 (CET) Date: Wed, 7 Nov 2018 17:44:44 +0100 From: Oleg Nesterov To: Andy Lutomirski Cc: Elvira Khabirova , rostedt@goodmis.org, mingo@redhat.com, linux-kernel@vger.kernel.org, ldv@altlinux.org, esyr@redhat.com, luto@kernel.org, strace-devel@lists.strace.io Subject: Re: [RFC PATCH] ptrace: add PTRACE_GET_SYSCALL_INFO request Message-ID: <20181107164443.GA8726@redhat.com> References: <20181107042751.3b519062@akathisia> <20181107112100.GA20419@redhat.com> <3BDB914D-12F3-4703-A033-EBE02226EC45@amacapital.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <3BDB914D-12F3-4703-A033-EBE02226EC45@amacapital.net> 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 [10.5.110.38]); Wed, 07 Nov 2018 16:44:52 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/07, Andy Lutomirski wrote: > > > > On Nov 7, 2018, at 3:21 AM, Oleg Nesterov wrote: > > > >> On 11/07, Elvira Khabirova wrote: > >> > >> In short, if a 64-bit task performs a syscall through int 0x80, its tracer > >> has no reliable means to find out that the syscall was, in fact, > >> a compat syscall, and misidentifies it. > >> * Syscall-enter-stop and syscall-exit-stop look the same for the tracer. > > > > Yes, this was discussed many times... > > > > So perhaps it makes sense to encode compat/is_enter in ->ptrace_message, > > debugger can use PTRACE_GETEVENTMSG to get this info. > > As I said before, I strongly object to the use of “compat” here. Not sure I understand you... I do not like "compat" too, but this patch uses is_compat/etc and I agree with any naming. > >> Secondly, ptracers also have to support a lot of arch-specific code for > >> obtaining information about the tracee. For some architectures, this > >> requires a ptrace(PTRACE_PEEKUSER, ...) invocation for every syscall > >> argument and return value. > > > > I am not sure about this change... I won't really argue, but imo this > > needs a separate patch. > > Why? Having a single struct that the tracer can read to get the full state is extremely helpful. As I said, I won't argue, but why can't it come as a separate change? More info in ->ptrace_message looks usable even without PTRACE_GET_SYSCALL_INFO, while ptrace_syscall_info layout/API may need more discussion. > Also, we really want it to work for seccomp events as well as PTRACE_SYSCALL, and the event info trick doesn’t make sense for seccomp events. I too thought about PTRACE_EVENT_SECCOMP (or I misunderstoo you?), looks like another reason to make a separate patch. > >> +#define PT_IN_SYSCALL_STOP 0x00000004 /* task is in a syscall-stop */ > > ... > >> -static inline int ptrace_report_syscall(struct pt_regs *regs) > >> +static inline int ptrace_report_syscall(struct pt_regs *regs, > >> + unsigned long message) > >> { > >> int ptrace = current->ptrace; > >> > >> if (!(ptrace & PT_PTRACED)) > >> return 0; > >> + current->ptrace |= PT_IN_SYSCALL_STOP; > >> > >> + current->ptrace_message = message; > >> ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0)); > >> > >> /* > >> @@ -76,6 +79,7 @@ static inline int ptrace_report_syscall(struct pt_regs *regs) > >> current->exit_code = 0; > >> } > >> > >> + current->ptrace &= ~PT_IN_SYSCALL_STOP; > >> return fatal_signal_pending(current); > > ... > > > >> + case PTRACE_GET_SYSCALL_INFO: > >> + if (child->ptrace & PT_IN_SYSCALL_STOP) > >> + ret = ptrace_get_syscall(child, datavp); > >> + break; > > > > Why? If debugger uses PTRACE_O_TRACESYSGOOD it can know if the tracee reported > > syscall entry/exit or not. PTRACE_GET_SYSCALL_INFO is pointless if not, but > > nothing bad can happen. > > I think it’s considerably nicer to the user to avoid reporting garbage if the user misused the API. (And Elvira got this right in the patch — I just missed it.) To me PT_IN_SYSCALL_STOP makes no real sense, but I won't argue. At least I'd ask to not abuse task->ptrace. ptrace_report_syscall() can clear ->ptrace_message on exit if we really want PTRACE_GET_SYSCALL_INFO to fail after that. Oleg.