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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 12DCCC433F4 for ; Tue, 28 Aug 2018 11:38:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B0CA42087D for ; Tue, 28 Aug 2018 11:38:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B0CA42087D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=alien8.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727433AbeH1P3b (ORCPT ); Tue, 28 Aug 2018 11:29:31 -0400 Received: from mail.skyhub.de ([5.9.137.197]:33086 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727067AbeH1P3b (ORCPT ); Tue, 28 Aug 2018 11:29:31 -0400 X-Virus-Scanned: Nedap ESD1 at mail.skyhub.de Received: from mail.skyhub.de ([127.0.0.1]) by localhost (blast.alien8.de [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id rcQ7ZrI5rsLJ; Tue, 28 Aug 2018 13:37:57 +0200 (CEST) Received: from nazgul.tnic (46-10-68-224.ip.btc-net.bg [46.10.68.224]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 439051EC02D1; Tue, 28 Aug 2018 13:37:57 +0200 (CEST) Date: Tue, 28 Aug 2018 13:36:11 +0200 From: Borislav Petkov To: Jann Horn Cc: Kees Cook , Thomas Gleixner , Ingo Molnar , x86@kernel.org, Andy Lutomirski , kernel-hardening@lists.openwall.com, Tony Luck , linux-kernel@vger.kernel.org, dvyukov@google.com, linux-edac@vger.kernel.org Subject: Re: [PATCH v2 1/7] x86: refactor kprobes_fault() like kprobe_exceptions_notify() Message-ID: <20180828113611.GC32231@nazgul.tnic> References: <20180827185631.163506-1-jannh@google.com> <20180827185631.163506-2-jannh@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180827185631.163506-2-jannh@google.com> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 27, 2018 at 08:56:25PM +0200, Jann Horn wrote: > This is an extension of commit b506a9d08bae ("x86: code clarification patch > to Kprobes arch code"). As that commit explains, even though > kprobe_running() can't be called with preemption enabled, you don't have to > disable preemption - if preemption is on, you can't be in a kprobe. > > Also, use X86_TRAP_PF instead of 14. > > Signed-off-by: Jann Horn > --- > arch/x86/mm/fault.c | 19 ++++++++----------- > 1 file changed, 8 insertions(+), 11 deletions(-) > > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c > index b9123c497e0a..2254a30533b9 100644 > --- a/arch/x86/mm/fault.c > +++ b/arch/x86/mm/fault.c > @@ -44,17 +44,14 @@ kmmio_fault(struct pt_regs *regs, unsigned long addr) > > static nokprobe_inline int kprobes_fault(struct pt_regs *regs) > { > - int ret = 0; > - > - /* kprobe_running() needs smp_processor_id() */ > - if (kprobes_built_in() && !user_mode(regs)) { > - preempt_disable(); > - if (kprobe_running() && kprobe_fault_handler(regs, 14)) > - ret = 1; > - preempt_enable(); > - } > - > - return ret; > + /* > + * To be potentially processing a kprobe fault and to be allowed to call > + * kprobe_running(), we have to be non-preemptible. > + */ > + if (kprobes_built_in() && !user_mode(regs) && !preemptible() && > + kprobe_running() && kprobe_fault_handler(regs, X86_TRAP_PF)) > + return 1; > + return 0; Maybe even: return (kprobes_built_in() && !user_mode(regs) && !preemptible() && kprobe_running() && kprobe_fault_handler(regs, X86_TRAP_PF)); Although I'd do it a bit more readable by flipping the checks and splitting them: if (!kprobes_built_in()) return 0; if (user_mode(regs)) return 0; ... return kprobe_fault_handler(regs, X86_TRAP_PF); } -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. --