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=-4.0 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 F311DC433E0 for ; Wed, 12 Aug 2020 09:30:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D91232076B for ; Wed, 12 Aug 2020 09:30:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727032AbgHLJaz (ORCPT ); Wed, 12 Aug 2020 05:30:55 -0400 Received: from mx2.suse.de ([195.135.220.15]:33812 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726595AbgHLJaz (ORCPT ); Wed, 12 Aug 2020 05:30:55 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 99660AEAC; Wed, 12 Aug 2020 09:31:15 +0000 (UTC) Date: Wed, 12 Aug 2020 11:31:14 +0200 From: Cyril Hrubis To: Andy Lutomirski Cc: Peter Zijlstra , Alexandre Chartre , kernel test robot , LKML , lkp@lists.01.org, Thomas Gleixner , ltp@lists.linux.it Subject: Re: [LTP] [x86/entry] 2bbc68f837: ltp.ptrace08.fail Message-ID: <20200812093114.GA13676@yuki.lan> References: <87y2onbdtb.fsf@nanos.tec.linutronix.de> <8E41B15F-D567-4C52-94E9-367015480345@amacapital.net> <20200616132705.GW2531@hirez.programming.kicks-ass.net> <20200617131742.GD8389@yuki.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi! > do_debug is a bit of a red herring here. ptrace should not be able to > put a breakpoint on a kernel address, period. I would just pick a > fixed address that's in the kernel text range or even just in the > pre-KASLR text range and make sure it gets rejected. Maybe try a few > different addresses for good measure. I've looked at the code and it seems like this would be a bit more complicated since the breakpoint is set by an accident in a race and the call still fails. Which is why the test triggers the breakpoint and causes infinite loop in the kernel... I guess that we could instead read back the address with PTRACE_PEEKUSER, so something as: break_addr = ptrace(PTRACE_PEEKUSER, child_pid, (void *)offsetof(struct user, u_debugreg[0]), NULL); if (break_addr == kernel_addr) tst_res(TFAIL, "ptrace() set break on a kernel address"); -- Cyril Hrubis chrubis@suse.cz