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=-6.8 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 4A0BFC433E7 for ; Wed, 2 Sep 2020 15:46:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 18A18208B3 for ; Wed, 2 Sep 2020 15:46:43 +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="Zke8VF7u" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728508AbgIBPqk (ORCPT ); Wed, 2 Sep 2020 11:46:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60964 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727041AbgIBNj3 (ORCPT ); Wed, 2 Sep 2020 09:39:29 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8E2F2C06125F for ; Wed, 2 Sep 2020 06:38:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-ID:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:In-Reply-To; bh=/Oowka1+4HYHH/M2f74f3FfCfCIjB94/ju74cCoLjd0=; b=Zke8VF7uLsaMj/PYECiOBSSFvx H2sjuKM4vy4ESU9+EBXJmoBD3INTmxkO22LgyRbJy3XGaGiDc1c7NJ5Nf1uYo09Aufh7zIxfWZWEV 3gW3xO6vmhkvQ+CL65ZwbEWsrrZTi7CH+qnRotbRdH8VTd7ZDf1w8w3IAPm+xdI/ZDTbm93OrO1aR JtoVSMaYM9RrOaFJDe7p71yQYsB8NN+ZAkHQe5HFla6vPjXbK9uz1ZeWsRy4gXHXyiCyprdbyk+UB GN6evDmF/s1hssbSrL8CklkQusl9WZcyh0BwihIxbafiyU9gu5KkGLa3t6cJsAk8DT2AWmFjNtBf0 do3L5JTg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kDSxs-0002dn-7k; Wed, 02 Sep 2020 13:38:16 +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 A7256307697; Wed, 2 Sep 2020 15:38:12 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id E2A4E29A82C29; Wed, 2 Sep 2020 15:38:11 +0200 (CEST) Message-ID: <20200902133201.354220797@infradead.org> User-Agent: quilt/0.66 Date: Wed, 02 Sep 2020 15:26:01 +0200 From: Peter Zijlstra To: x86@kernel.org Cc: linux-kernel@vger.kernel.org, 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 , Brian Gerst , Andy Lutomirski , Josh Poimboeuf , Daniel Thompson , Peter Zijlstra , Andrew Cooper Subject: [RFC][PATCH 12/13] x86/debug: Support negative polarity DR6 bits References: <20200902132549.496605622@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org DR6 has a whole bunch of bits that have negative polarity; they were architecturally reserved and defined to be 1 and are now getting used. Since they're 1 by default, 0 becomes the signal value. Handle this by xor'ing the read DR6 value by the reserved mask, this will flip them around such that 1 is the signal value (positive polarity). Current Linux doesn't yet support any of these bits, but there's two defined: - DR6[11] Bus Lock Debug Exception (ISEr39) - DR6[16] Restricted Transactional Memory (SDM) Update ptrace_{set,get}_debugreg() to provide/consume the value in architectural polarity. Although afaict ptrace_set_debugreg(6) is pointless, the value is not consumed anywhere. Change hw_breakpoint_restore() to alway write the DR6_RESERVED value to DR6, again, no consumer for that write. Suggested-by: Andrew Cooper Signed-off-by: Peter Zijlstra (Intel) --- arch/x86/kernel/hw_breakpoint.c | 2 +- arch/x86/kernel/ptrace.c | 4 ++-- arch/x86/kernel/traps.c | 5 ++--- 3 files changed, 5 insertions(+), 6 deletions(-) --- a/arch/x86/kernel/hw_breakpoint.c +++ b/arch/x86/kernel/hw_breakpoint.c @@ -500,7 +500,7 @@ void hw_breakpoint_restore(void) set_debugreg(__this_cpu_read(cpu_debugreg[1]), 1); set_debugreg(__this_cpu_read(cpu_debugreg[2]), 2); set_debugreg(__this_cpu_read(cpu_debugreg[3]), 3); - set_debugreg(current->thread.debugreg6, 6); + set_debugreg(DR6_RESERVED, 6); set_debugreg(__this_cpu_read(cpu_dr7), 7); } EXPORT_SYMBOL_GPL(hw_breakpoint_restore); --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -601,7 +601,7 @@ static unsigned long ptrace_get_debugreg if (bp) val = bp->hw.info.address; } else if (n == 6) { - val = thread->debugreg6; + val = thread->debugreg6 ^ DR6_RESERVED; /* Flip back to arch polarity */ } else if (n == 7) { val = thread->ptrace_dr7; } @@ -657,7 +657,7 @@ static int ptrace_set_debugreg(struct ta if (n < HBP_NUM) { rc = ptrace_set_breakpoint_addr(tsk, n, val); } else if (n == 6) { - thread->debugreg6 = val; + thread->debugreg6 = val ^ DR6_RESERVED; /* Flip to positive polarity */ rc = 0; } else if (n == 7) { rc = ptrace_write_dr7(tsk, val); --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -745,9 +745,8 @@ static __always_inline unsigned long deb * Keep it simple: clear DR6 immediately. */ get_debugreg(dr6, 6); - set_debugreg(0, 6); - /* Filter out all the reserved bits which are preset to 1 */ - dr6 &= ~DR6_RESERVED; + set_debugreg(DR6_RESERVED, 6); + dr6 ^= DR6_RESERVED; /* Flip to positive polarity */ /* * The SDM says "The processor clears the BTF flag when it