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=-5.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 4F544C11D04 for ; Thu, 20 Feb 2020 12:38:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2159924670 for ; Thu, 20 Feb 2020 12:38:35 +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="PmaWFZbV" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727987AbgBTMid (ORCPT ); Thu, 20 Feb 2020 07:38:33 -0500 Received: from merlin.infradead.org ([205.233.59.134]:52392 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726885AbgBTMid (ORCPT ); Thu, 20 Feb 2020 07:38:33 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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=bcJGrENIxStVO5U2yoDpjYTpnIM80UF8M699WOXfM+8=; b=PmaWFZbV67o/inyTG2Fa5dNjrZ Wvcg2n6QFFc10N1cG2b/GrrA0ArZL1vuzUxp3zuGX8RiH6wMjoH7SWkVcM+WX9D6yQG7j1EUSjkxb +4ebrcrc3Znbvvjv1rNT29Dugq6FH5A4a8gM8CmT6hr8KUwvZPXjrMrAKBK53msZmPjhnFvHn2WkZ x80Dt3WM+FAShlSx44RIinSrAfbJEaV5H0B9WpJGfxTAsZnKc/mOkky6ACxDtd4XF4GGsIY0vaIsn m7RkFTIS2b6UIk8wz9KNPNebJRl28+/evRKyqHKXstnknH1dR5kpyUFDAEyA9VTP4X44ZJiIayOAf 451yDgQw==; 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 1j4l5O-0003xf-4U; Thu, 20 Feb 2020 12:37:46 +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 BB2F6300565; Thu, 20 Feb 2020 13:35:49 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 7EAAA2B4D9BC7; Thu, 20 Feb 2020 13:37:42 +0100 (CET) Date: Thu, 20 Feb 2020 13:37:42 +0100 From: Peter Zijlstra To: Borislav Petkov 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: <20200220123742.GZ18400@hirez.programming.kicks-ass.net> 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> <20200220121727.GB507@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200220121727.GB507@zn.tnic> 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 Thu, Feb 20, 2020 at 01:17:27PM +0100, Borislav Petkov wrote: > 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 */ > > /* While I love that; is that actually correct? This is an unroll of memcpy() not memmove(). IFF the ranges overlap, the above is buggered. Was the original memmove() really needed?