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=-8.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 D650DC433E0 for ; Fri, 5 Jun 2020 16:42:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AAE432077D for ; Fri, 5 Jun 2020 16:42:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="C8r73mxW" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726192AbgFEQm5 (ORCPT ); Fri, 5 Jun 2020 12:42:57 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:50572 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725961AbgFEQm4 (ORCPT ); Fri, 5 Jun 2020 12:42:56 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1591375374; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=bdEGpZ06r/Y0nQCCHtiMh+9RZsiujmklfqlTK0kVMWY=; b=C8r73mxW26ju2I5z6ra4baQ3CTWB+HOr9bT0Tt+En3AIsd9jQMe5enfAEakHI8O91GOWZ9 Yq1ny3QitH7jN+UBGsu9niWDd5cK4MNedqsnXWOaskXhTyO0JkC+m7jdZLYcBHp+ngFgLV lYgmb+sf7MpHFHe+mITc17XYDMnWwsw= 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-212-1-nvlzMDPPOd3JyJIWPl1w-1; Fri, 05 Jun 2020 12:42:50 -0400 X-MC-Unique: 1-nvlzMDPPOd3JyJIWPl1w-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6E36A107ACF5; Fri, 5 Jun 2020 16:42:48 +0000 (UTC) Received: from prarit.bos.redhat.com (prarit-guest.7a2m.lab.eng.bos.redhat.com [10.16.222.26]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0EF8C19C58; Fri, 5 Jun 2020 16:42:45 +0000 (UTC) Subject: Re: [PATCH] x86/split_lock: Sanitize userspace and guest error output To: Xiaoyao Li , linux-kernel@vger.kernel.org Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Tony Luck , "Peter Zijlstra (Intel)" , Sean Christopherson , Rahul Tanwar , Ricardo Neri , Dave Hansen References: <20200605114459.22200-1-prarit@redhat.com> <96b5c5fa-6b4e-a5f4-34cc-682477a27370@intel.com> From: Prarit Bhargava Message-ID: <3e1f1fac-fa46-7a2a-1424-d5c931e521d7@redhat.com> Date: Fri, 5 Jun 2020 12:42:45 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <96b5c5fa-6b4e-a5f4-34cc-682477a27370@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/5/20 11:29 AM, Xiaoyao Li wrote: > On 6/5/2020 7:44 PM, Prarit Bhargava wrote: >> There are two problems with kernel messages in fatal mode that >> were found during testing of guests and userspace programs. >> >> The first is that no kernel message is output when the split lock detector >> is triggered with a userspace program.  As a result the userspace process >> dies from receiving SIGBUS with no indication to the user of what caused >> the process to die. >> >> The second problem is that only the first triggering guest causes a kernel >> message to be output because the message is output with pr_warn_once(). >> This also results in a loss of information to the user. >> >> While fixing these I noticed that the same message was being output >> three times so I'm cleaning that up too. >> >> Fix fatal mode output, and use consistent messages for fatal and >> warn modes for both userspace and guests. >> >> Signed-off-by: Prarit Bhargava >> Cc: Thomas Gleixner >> Cc: Ingo Molnar >> Cc: Borislav Petkov >> Cc: x86@kernel.org >> Cc: "H. Peter Anvin" >> Cc: Tony Luck >> Cc: "Peter Zijlstra (Intel)" >> Cc: Sean Christopherson >> Cc: Rahul Tanwar >> Cc: Xiaoyao Li >> Cc: Ricardo Neri >> Cc: Dave Hansen >> --- >>   arch/x86/kernel/cpu/intel.c | 24 ++++++++++-------------- >>   1 file changed, 10 insertions(+), 14 deletions(-) >> >> diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c >> index 166d7c355896..463022aa9b7a 100644 >> --- a/arch/x86/kernel/cpu/intel.c >> +++ b/arch/x86/kernel/cpu/intel.c >> @@ -1074,10 +1074,14 @@ static void split_lock_init(void) >>       split_lock_verify_msr(sld_state != sld_off); >>   } >>   -static void split_lock_warn(unsigned long ip) >> +static bool split_lock_warn(unsigned long ip, int fatal) >>   { >> -    pr_warn_ratelimited("#AC: %s/%d took a split_lock trap at address: 0x%lx\n", >> -                current->comm, current->pid, ip); >> +    pr_warn_ratelimited("#AC: %s/%d %ssplit_lock trap at address: 0x%lx\n", >> +                current->comm, current->pid, >> +                sld_state == sld_fatal ? "fatal " : "", ip); >> + >> +    if (sld_state == sld_fatal || fatal) >> +        return false; >>         /* >>        * Disable the split lock detection for this task so it can make >> @@ -1086,18 +1090,13 @@ static void split_lock_warn(unsigned long ip) >>        */ >>       sld_update_msr(false); >>       set_tsk_thread_flag(current, TIF_SLD); >> +    return true; >>   } >>     bool handle_guest_split_lock(unsigned long ip) >>   { >> -    if (sld_state == sld_warn) { >> -        split_lock_warn(ip); >> +    if (split_lock_warn(ip, 0)) >>           return true; >> -    } >> - >> -    pr_warn_once("#AC: %s/%d %s split_lock trap at address: 0x%lx\n", >> -             current->comm, current->pid, >> -             sld_state == sld_fatal ? "fatal" : "bogus", ip); >>         current->thread.error_code = 0; >>       current->thread.trap_nr = X86_TRAP_AC; >> @@ -1108,10 +1107,7 @@ EXPORT_SYMBOL_GPL(handle_guest_split_lock); >>     bool handle_user_split_lock(struct pt_regs *regs, long error_code) >>   { >> -    if ((regs->flags & X86_EFLAGS_AC) || sld_state == sld_fatal) >> -        return false; >> -    split_lock_warn(regs->ip); >> -    return true; >> +    return split_lock_warn(regs->ip, regs->flags & X86_EFLAGS_AC); > > It's incorrect. You change the behavior that it will print the split lock > warning even when CPL 3 Alignment Check is turned on. Do you want the message to be displayed in the fatal case of CPL 3 Alignment check? P.