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=-2.1 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, 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 122B8C6778C for ; Tue, 3 Jul 2018 17:49:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B73A9208B1 for ; Tue, 3 Jul 2018 17:49:53 +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="Kc5W/hj+" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B73A9208B1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org 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 S934372AbeGCRtu (ORCPT ); Tue, 3 Jul 2018 13:49:50 -0400 Received: from merlin.infradead.org ([205.233.59.134]:47164 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934187AbeGCRts (ORCPT ); Tue, 3 Jul 2018 13:49:48 -0400 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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=xnUtUyUdlgEeaCkjd4iQHwYvQFix1UZqe+IlFrzhsz8=; b=Kc5W/hj+vQZfKPX/Y1ewqZWV0 vEUQkrXN1o6d/4kUOzBMWVS8ZKd8hB7IMc3wV7f0Tnrdewufn0ukUmt4UKuyHts0Q1LePnIjFLvWJ lrRvNj/jM7hVby3BGPSQMlZGMogb2USzgCGV2f7OCMqNy8KAthKKonrI5XyJtUE/w4EnR6QvBUors HKTiKQtYZCl8GJgvQ6C2BH1AQPfb5SdYR7CR0hkfnrtt9u4ZR91uMHkFwktWln3+nErWMZjRu1myA rB2gnUPvZcEXDhMpTUc3mEUIXrOrn4z3XqcSiI+iSck+QmNdUT3gETwUNBRhLhberaMSkgQ0M8O2Z ygXa6rs+Q==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1faPPn-0004Bb-1L; Tue, 03 Jul 2018 17:48:35 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id B5C352029764D; Tue, 3 Jul 2018 19:48:33 +0200 (CEST) Date: Tue, 3 Jul 2018 19:48:33 +0200 From: Peter Zijlstra To: Mathieu Desnoyers Cc: Linus Torvalds , Andi Kleen , heiko carstens , Andy Lutomirski , Thomas Gleixner , linux-kernel , linux-api , "Paul E. McKenney" , Boqun Feng , Dave Watson , Paul Turner , Andrew Morton , Russell King , Ingo Molnar , "H. Peter Anvin" , Chris Lameter , Ben Maurer , rostedt , Josh Triplett , Catalin Marinas , Will Deacon , Michael Kerrisk , Joel Fernandes , Michal Simek , schwidefsky , gor Subject: Re: [RFC PATCH for 4.18] rseq: use __u64 for rseq_cs fields, validate user inputs Message-ID: <20180703174833.GZ2494@hirez.programming.kicks-ass.net> References: <858886246.10882.1530583291379.JavaMail.zimbra@efficios.com> <20180703082955.GH3704@osiris> <20180703084312.GU2494@hirez.programming.kicks-ass.net> <20180703085546.GJ3704@osiris> <20180703092113.GV2494@hirez.programming.kicks-ass.net> <20180703164048.i2te5gjemcafqzwf@two.firstfloor.org> <20180703173451.GX2494@hirez.programming.kicks-ass.net> <399697782.11820.1530639539750.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <399697782.11820.1530639539750.JavaMail.zimbra@efficios.com> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 03, 2018 at 01:38:59PM -0400, Mathieu Desnoyers wrote: > ----- On Jul 3, 2018, at 1:34 PM, Peter Zijlstra peterz@infradead.org wrote: > > > On Tue, Jul 03, 2018 at 10:10:37AM -0700, Linus Torvalds wrote: > >> On Tue, Jul 3, 2018 at 9:40 AM Andi Kleen wrote: > >> > > >> > So it sounds like architectures that don't have an instruction atomic u64 > >> > *_user need to disable interrupts during the access, and somehow handle that > >> > case when a page fault happens? > >> > >> No. It's actually the store by *user* space that is the critical one. > >> Not the whole 64-bit value, just the low pointer part. > >> > >> The kernel could do it as a byte-by-byte load, really. It's > >> per-thread, and once the kernel is running, it's not going to change. > >> The kernel never changes the value, it just loads it from user space. > > > > The kernel doesn't change _this_ value, but the kernel does change other > > values, like for instance rseq->cpu_id. But even there, it could use > > byte stores and it is again the userspace load of that field that is > > critical again and needs to be a single op. > > I can simply document that loads/stores from/to all struct rseq fields > should be thread-local then ? I'm not sure that covers things sufficiently. You really want the userspace load/stores to be single instructions. Also, I think it was rseq_update_cpu_id() where we wanted to use a single u64 store if possible but you worried about the stores.