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=-6.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 BEDC8C433DF for ; Thu, 20 Aug 2020 15:21:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 98EB1206DA for ; Thu, 20 Aug 2020 15:21:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="CdQPS5aH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728689AbgHTPVx (ORCPT ); Thu, 20 Aug 2020 11:21:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55028 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726852AbgHTPVw (ORCPT ); Thu, 20 Aug 2020 11:21:52 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6A500C061385 for ; Thu, 20 Aug 2020 08:21:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=WO117o7rJcvrbn+tJaLD6rskyy5H89U6ereeOLtJe1c=; b=CdQPS5aHR7EtJZbvyYojM200RK Oog4l+FWkvps1fksUvEm2LgpR8YoCNcGlaZ7ahdVeikJxopfqkNGCTKwbbDa0xO7fSURL6vdQVyIV GuTi0blZ33rKqdURzQq2jg4gdfXT03Bsy9zqMQoYYfC0ruwfmA3Q2Wv3Kzk1MktcCffSaNoSo8CWN y4UNc3bH35nfRVz+0Xp422bGg9aWyde/ukgOTbYJaqcJxxaseiFStDfHtsqM6ubv3zp929BzXsPKH a2Mn9KUzg+MJLWdetibJ938MrojI2GRnPohlrWp4y78KUX2QZUPjpiuJMZZfk7MER3nZCFgnHwLO+ E8rxPj9A==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1k8mNN-000654-0z; Thu, 20 Aug 2020 15:21:13 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id F3C16302526; Thu, 20 Aug 2020 17:21:11 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id DD97A21296C3B; Thu, 20 Aug 2020 17:21:11 +0200 (CEST) Date: Thu, 20 Aug 2020 17:21:11 +0200 From: peterz@infradead.org To: Josh Poimboeuf Cc: Brian Gerst , the arch/x86 maintainers , Linux Kernel Mailing List , Kyle Huey , Alexandre Chartre , Robert O'Callahan , "Paul E. McKenney" , Frederic Weisbecker , Paolo Bonzini , Sean Christopherson , Masami Hiramatsu , Petr Mladek , Steven Rostedt , Joel Fernandes , Boris Ostrovsky , Juergen Gross , Andy Lutomirski Subject: Re: [RFC][PATCH 4/7] x86/debug: Move historical SYSENTER junk into exc_debug_kernel() Message-ID: <20200820152111.GC1362448@hirez.programming.kicks-ass.net> References: <20200820103832.486877479@infradead.org> <20200820104905.294802764@infradead.org> <20200820150841.GB1362448@hirez.programming.kicks-ass.net> <20200820151659.b7q7hspe5zsf46eg@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200820151659.b7q7hspe5zsf46eg@treble> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 20, 2020 at 10:16:59AM -0500, Josh Poimboeuf wrote: > On Thu, Aug 20, 2020 at 05:08:41PM +0200, peterz@infradead.org wrote: > > On Thu, Aug 20, 2020 at 10:45:12AM -0400, Brian Gerst wrote: > > > On Thu, Aug 20, 2020 at 6:53 AM Peter Zijlstra wrote: > > > > > > > > > > > > Signed-off-by: Peter Zijlstra (Intel) > > > > --- > > > > arch/x86/kernel/traps.c | 24 ++++++++++++------------ > > > > 1 file changed, 12 insertions(+), 12 deletions(-) > > > > > > > > --- a/arch/x86/kernel/traps.c > > > > +++ b/arch/x86/kernel/traps.c > > > > @@ -820,18 +820,6 @@ static void handle_debug(struct pt_regs > > > > goto out; > > > > } > > > > > > > > - if (WARN_ON_ONCE((dr6 & DR_STEP) && !user_mode(regs))) { > > > > - /* > > > > - * Historical junk that used to handle SYSENTER single-stepping. > > > > - * This should be unreachable now. If we survive for a while > > > > - * without anyone hitting this warning, we'll turn this into > > > > - * an oops. > > > > - */ > > > > - tsk->thread.debugreg6 &= ~DR_STEP; > > > > - set_tsk_thread_flag(tsk, TIF_SINGLESTEP); > > > > - regs->flags &= ~X86_EFLAGS_TF; > > > > - } > > > > - > > > > si_code = get_si_code(tsk->thread.debugreg6); > > > > if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS) || user_icebp) > > > > send_sigtrap(regs, 0, si_code); > > > > @@ -874,6 +862,18 @@ static __always_inline void exc_debug_ke > > > > if (kprobe_debug_handler(regs)) > > > > goto out; > > > > > > > > + if (WARN_ON_ONCE(dr6 & DR_STEP)) { > > > > + /* > > > > + * Historical junk that used to handle SYSENTER single-stepping. > > > > + * This should be unreachable now. If we survive for a while > > > > + * without anyone hitting this warning, we'll turn this into > > > > + * an oops. > > > > + */ > > > > + dr6 &= ~DR_STEP; > > > > + set_thread_flag(TIF_SINGLESTEP); > > > > + regs->flags &= ~X86_EFLAGS_TF; > > > > + } > > > > + > > > > handle_debug(regs, dr6, false); > > > > > > > > out: > > > > > > Can this be removed or changed to a BUG()? The warning has been there > > > since 2016 and nobody has apparently complained about it. > > > > Something like: > > > > /* > > * The kernel doesn't do TF outside of Kprobes, so if we get > > * here, something's fishy. > > */ > > BUG_ON(dr6 & DR_STEP); > > > > ? > > What about kernel debuggers like kgdb and qemu gdb? qemu-gdb stub should eat the event before it lands in the guest, kgdb should eat it through the notifier. Thank you! Because that means I got the order wrong :/