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=-5.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,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 EE675C11D04 for ; Thu, 20 Feb 2020 12:17:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C06CD207FD for ; Thu, 20 Feb 2020 12:17:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="fJVY7q+g" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727915AbgBTMRe (ORCPT ); Thu, 20 Feb 2020 07:17:34 -0500 Received: from mail.skyhub.de ([5.9.137.197]:45908 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726893AbgBTMRe (ORCPT ); Thu, 20 Feb 2020 07:17:34 -0500 Received: from zn.tnic (p200300EC2F0ADE008C2E3AE544E50E0D.dip0.t-ipconnect.de [IPv6:2003:ec:2f0a:de00:8c2e:3ae5:44e5:e0d]) (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 C76071EC0304; Thu, 20 Feb 2020 13:17:32 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1582201052; 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:in-reply-to:in-reply-to: references:references; bh=GHsRYld0xfiWTAFa2iAQEWWjuxSWqN7yTT7gbGMHIis=; b=fJVY7q+gdDI0ItvEVUNDDOPRWGNPal8VzHyxsdcxN906vvkCWwEDWjUqmb0kz8lAh/yY+q 1VOS4XNZcQl5APvPctdgQ7FptOHdrPsfwEEhUx04gT+okd6yBmt0X9ObeDAvj8qj8gvsnT R1spuYpWhS+l5BNHr5PDkcvzsGs6umc= Date: Thu, 20 Feb 2020 13:17:27 +0100 From: Borislav Petkov To: Peter Zijlstra Cc: Steven Rostedt , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, mingo@kernel.org, joel@joelfernandes.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, paulmck@kernel.org, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, luto@kernel.org, tony.luck@intel.com, frederic@kernel.org, dan.carpenter@oracle.com, mhiramat@kernel.org Subject: Re: [PATCH v3 04/22] x86/doublefault: Make memmove() notrace/NOKPROBE Message-ID: <20200220121727.GB507@zn.tnic> References: <20200219144724.800607165@infradead.org> <20200219150744.604459293@infradead.org> <20200219103614.2299ff61@gandalf.local.home> <20200219154031.GE18400@hirez.programming.kicks-ass.net> <20200219155715.GD14946@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200219155715.GD14946@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 19, 2020 at 04:57:15PM +0100, Peter Zijlstra wrote: > - memmove(&gpregs->ip, (void *)regs->sp, 5*8); > + for (i = 0; i < count; i++) { > + int idx = (dst <= src) ? i : count - i; > + dst[idx] = src[idx]; > + } Or, you can actually unroll it. This way it even documents clearly what it does: diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index fe38015ed50a..2b790a574ba5 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -298,6 +298,7 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code, unsign regs->ip == (unsigned long)native_irq_return_iret) { struct pt_regs *gpregs = (struct pt_regs *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1; + unsigned long *p = (unsigned long *)regs->sp; /* * regs->sp points to the failing IRET frame on the @@ -305,7 +306,11 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code, unsign * in gpregs->ss through gpregs->ip. * */ - memmove(&gpregs->ip, (void *)regs->sp, 5*8); + gpregs->ip = *p; + gpregs->cs = *(p + 1); + gpregs->flags = *(p + 2); + gpregs->sp = *(p + 3); + gpregs->ss = *(p + 4); gpregs->orig_ax = 0; /* Missing (lost) #GP error code */ /* -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette