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=-5.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 0A5C9C2D0A3 for ; Tue, 3 Nov 2020 12:50:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9D58E20731 for ; Tue, 3 Nov 2020 12:50:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="VMsEE6Y1" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728745AbgKCMuq (ORCPT ); Tue, 3 Nov 2020 07:50:46 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:34873 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726388AbgKCMuq (ORCPT ); Tue, 3 Nov 2020 07:50:46 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1604407844; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=czYSHEkJZRKBHJc6+H3B9w8RmjDMKNgYyM8LaMqolZw=; b=VMsEE6Y1zplAdZk7YralgLB5F1aOY65et04JnOngvOJSf9ocAandXhEcmmFWSM/68/yzG6 G2xGRywXTuWACnzWV20St/YTNkD5I25Rxxf48IhDOorAP0jsbazYlAxdg7bQKCMiSBnq2z qMsNgN2mQWUUwTSoPTSbzNJfhQY6VzE= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-572-8apJzIFdN-egZ6oA7GB6Hw-1; Tue, 03 Nov 2020 07:50:41 -0500 X-MC-Unique: 8apJzIFdN-egZ6oA7GB6Hw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id CFC81106C10A; Tue, 3 Nov 2020 12:50:38 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.195.6]) by smtp.corp.redhat.com (Postfix) with SMTP id CF925672C0; Tue, 3 Nov 2020 12:50:35 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 3 Nov 2020 13:50:38 +0100 (CET) Date: Tue, 3 Nov 2020 13:50:34 +0100 From: Oleg Nesterov To: Mark Mossberg Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, linux-kernel@vger.kernel.org, hpa@zytor.com, jannh@google.com, kyin@redhat.com Subject: Re: [PATCH v2] x86/dumpstack: Fix misleading instruction pointer error message Message-ID: <20201103125034.GA30391@redhat.com> References: <20201002042915.403558-1-mark.mossberg@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201002042915.403558-1-mark.mossberg@gmail.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/02, Mark Mossberg wrote: > > Printing "Bad RIP value" if copy_code() fails can be misleading for > userspace pointers, since copy_code() can fail if the instruction > pointer is valid, but the code is paged out. Another problem is that show_opcodes() makes no sense if user_mode(regs) and tsk is not current. Try "echo t > /proc/sysrq-trigger". In this case copy_from_user_nmi() will either fail, or (worse) it will read the "random" memory from current->mm. Perhaps we can add something like if (user_mode(regs) && regs != task_pt_regs(current)) return; at the start of show_opcodes() ? > --- a/arch/x86/kernel/dumpstack.c > +++ b/arch/x86/kernel/dumpstack.c > @@ -115,7 +115,8 @@ void show_opcodes(struct pt_regs *regs, const char *loglvl) > unsigned long prologue = regs->ip - PROLOGUE_SIZE; > > if (copy_code(regs, opcodes, prologue, sizeof(opcodes))) { > - printk("%sCode: Bad RIP value.\n", loglvl); > + printk("%sCode: Unable to access opcode bytes at RIP 0x%lx.\n", > + loglvl, prologue); > } else { > printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %" > __stringify(EPILOGUE_SIZE) "ph\n", loglvl, opcodes, > -- > 2.25.1 >