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=-0.8 required=3.0 tests=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 52745C4332D for ; Fri, 20 Mar 2020 18:18:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2EFDC20777 for ; Fri, 20 Mar 2020 18:18:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727324AbgCTSSw (ORCPT ); Fri, 20 Mar 2020 14:18:52 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:36798 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726956AbgCTSSv (ORCPT ); Fri, 20 Mar 2020 14:18:51 -0400 Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jFMEF-0001ar-Fw; Fri, 20 Mar 2020 19:18:43 +0100 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 68807100375; Fri, 20 Mar 2020 19:18:42 +0100 (CET) From: Thomas Gleixner To: Paolo Bonzini , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: syzbot+00be5da1d75f1cc95f6b@syzkaller.appspotmail.com, Sean Christopherson Subject: Re: [PATCH] KVM: x86: remove bogus user-triggerable WARN_ON In-Reply-To: References: <20200319174318.20752-1-pbonzini@redhat.com> <87o8sr59v9.fsf@nanos.tec.linutronix.de> <87lfnv59u8.fsf@nanos.tec.linutronix.de> Date: Fri, 20 Mar 2020 19:18:42 +0100 Message-ID: <87tv2i7uv1.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paolo Bonzini writes: > On 20/03/20 16:23, Thomas Gleixner wrote: >> Thomas Gleixner writes: >> >>> Paolo Bonzini writes: >>>> The WARN_ON is essentially comparing a user-provided value with 0. It is >>>> trivial to trigger it just by passing garbage to KVM_SET_CLOCK. Guests >>>> can break if you do so, but if it hurts when you do like this just do not >>>> do it. >>> >>> Yes, it's a user provided value and it's completely unchecked. If that >>> value is bogus then the guest will go sideways because timekeeping is >>> completely busted. At least you should explain WHY you don't care. >> >> Or why it does not matter.... > > I can change the commit message to "Guests can break if you do so, but > the same applies to every KVM_SET_* ioctl". It's impossible to be sure > that userspace doesn't ever send a bogus KVM_SET_CLOCK and later > rectifies it with the right value. Yes please.