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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 25662C48BE5 for ; Mon, 21 Jun 2021 03:44:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DCE616120D for ; Mon, 21 Jun 2021 03:44:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230205AbhFUDq5 (ORCPT ); Sun, 20 Jun 2021 23:46:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54530 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229905AbhFUDq4 (ORCPT ); Sun, 20 Jun 2021 23:46:56 -0400 Received: from zeniv-ca.linux.org.uk (zeniv-ca.linux.org.uk [IPv6:2607:5300:60:148a::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 02863C061574; Sun, 20 Jun 2021 20:44:42 -0700 (PDT) Received: from viro by zeniv-ca.linux.org.uk with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1lvArR-00AhLi-66; Mon, 21 Jun 2021 03:44:33 +0000 Date: Mon, 21 Jun 2021 03:44:33 +0000 From: Al Viro To: Michael Schmitz Cc: Linus Torvalds , "Eric W. Biederman" , linux-arch , Jens Axboe , Oleg Nesterov , Linux Kernel Mailing List , Richard Henderson , Ivan Kokshaysky , Matt Turner , alpha , Geert Uytterhoeven , linux-m68k , Arnd Bergmann , Ley Foon Tan , Tejun Heo , Kees Cook Subject: Re: [PATCH 1/2] alpha/ptrace: Record and handle the absence of switch_stack Message-ID: References: <5929e116-fa61-b211-342a-c706dcb834ca@gmail.com> <87fsxjorgs.fsf@disp2133> <87zgvqor7d.fsf_-_@disp2133> <87mtrpg47k.fsf@disp2133> <87pmwlek8d.fsf_-_@disp2133> <87k0mtek4n.fsf_-_@disp2133> <393c37de-5edf-effc-3d06-d7e63f34a317@gmail.com> <60c0fe00-b966-6385-d348-f6dd45277113@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <60c0fe00-b966-6385-d348-f6dd45277113@gmail.com> Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 21, 2021 at 03:18:35PM +1200, Michael Schmitz wrote: > This is what I get from WARN_ONCE: > > ------------[ cut here ]------------ > WARNING: CPU: 0 PID: 1177 at arch/m68k/kernel/ptrace.c:91 get_reg+0x90/0xb8 > Modules linked in: > CPU: 0 PID: 1177 Comm: strace Not tainted 5.13.0-rc1-atari-fpuemu-exitfix+ > #1146 > Stack from 014b7f04: > 014b7f04 00336401 00336401 000278f0 0032c015 0000005b 00000005 > 0002795a > 0032c015 0000005b 0000338c 00000009 00000000 00000000 ffffffe4 > 00000005 > 00000003 00000014 00000003 00000014 efc2b90c 0000338c 0032c015 > 0000005b > 00000009 00000000 efc2b908 00912540 efc2b908 000034cc 00912540 > 00000005 > 00000000 efc2b908 00000003 00912540 8000110c c010b0a4 efc2b90c > 0002d1d8 > 00912540 00000003 00000014 efc2b908 0000049a 00000014 efc2b908 > 800acaa8 > Call Trace: [<000278f0>] __warn+0x9e/0xb4 > [<0002795a>] warn_slowpath_fmt+0x54/0x62 > [<0000338c>] get_reg+0x90/0xb8 > [<0000338c>] get_reg+0x90/0xb8 > [<000034cc>] arch_ptrace+0x7e/0x250 > [<0002d1d8>] sys_ptrace+0x232/0x2f8 > [<00002ab6>] syscall+0x8/0xc > [<0000c00b>] lower+0x7/0x20 > > ---[ end trace ee4be53b94695793 ]--- > > Syscall numbers are actually 90 and 192 - sys_old_mmap and sys_mmap2 on > m68k. Used the calculator on my Ubuntu desktop, that appears to be a little > confused about hex to decimal conversions. > > I hope that makes more sense? Not really; what is the condition you are checking? The interesting trace is not that with get_reg() - it's that of the process being traced. You are not accessing the stack of caller of ptrace(2) here, so you want to know that SAVE_SWITCH_STACK had been done by the tracee, not tracer. And if that had been strace ls, you have TIF_SYSCALL_TRACE set for ls, so * ls hits system_call * notices TIF_SYSCALL_TRACE and goes to do_trace_entry * does SAVE_SWITCH_STACK there * calls syscall_trace(), which calls ptrace_notify() * ptrace_notify() calls ptrace_do_notify(), which calls ptrace_stop() * ptrace_stop() arranges for tracer to be woken up and gives CPU up, with TASK_TRACED as process state. That's the callchain in ls, and switch_stack accessed by get_reg() from strace is the one on ls(1) stack created by SAVE_SWITCH_STACK.