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 5589BC6778A for ; Tue, 3 Jul 2018 08:43:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0F89323CCA for ; Tue, 3 Jul 2018 08:43:45 +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="DyXINB/E" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0F89323CCA 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 S932417AbeGCInl (ORCPT ); Tue, 3 Jul 2018 04:43:41 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:38250 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753834AbeGCInj (ORCPT ); Tue, 3 Jul 2018 04:43:39 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=/llqX1i+CcgaFGwDM5tJvs+dE0ZgjSLoTPJH4zR/4/Y=; b=DyXINB/ElFuuA9S8E8Y+9qP9K YAF1FFxaoa+snpanDTq2d9qJg8ktggVnPa7aI5SwO9JTvJGuCa2UMk6i1k8eBmdrB8FTpl+Q/9RsB 02v0OEisZ4oIlPC9fze1RlIrnTETPqS/jh1SsqtYKu+HZT8OPYsCk6tXuEXieJ/iEaS8dDRLlihyi uxS0ZUYEKzaKjQk8iVmJaid4XPNIM/jK9248ZDhlOYgCQVHkkSm0v1ZcLTuzgSfCZ8DAIlP1MJzb8 8L8/jyLKn/vU1ef6TVZDAacJL/ZRgi/0Sqz+AOHOlStE7K5TJcB+59HgFsVExxEpVkFOpx6uhowA+ TzxS2Z/xg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1faGu1-0004pH-OL; Tue, 03 Jul 2018 08:43:14 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 2788F2028932E; Tue, 3 Jul 2018 10:43:12 +0200 (CEST) Date: Tue, 3 Jul 2018 10:43:12 +0200 From: Peter Zijlstra To: Heiko Carstens Cc: Mathieu Desnoyers , Linus Torvalds , 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" , Andi Kleen , Chris Lameter , Ben Maurer , rostedt , Josh Triplett , Catalin Marinas , Will Deacon , Michael Kerrisk , Joel Fernandes , michal.simek@xilinx.com, Martin Schwidefsky , Vasily Gorbik Subject: Re: [RFC PATCH for 4.18] rseq: use __u64 for rseq_cs fields, validate user inputs Message-ID: <20180703084312.GU2494@hirez.programming.kicks-ass.net> References: <825871008.10839.1530573419561.JavaMail.zimbra@efficios.com> <1959930320.10843.1530573742647.JavaMail.zimbra@efficios.com> <8B2E4CEB-3080-4602-8B62-774E400892EB@amacapital.net> <459661281.10865.1530580742205.JavaMail.zimbra@efficios.com> <858886246.10882.1530583291379.JavaMail.zimbra@efficios.com> <1776351430.10902.1530585009519.JavaMail.zimbra@efficios.com> <20180703081449.GT2494@hirez.programming.kicks-ass.net> <20180703082955.GH3704@osiris> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180703082955.GH3704@osiris> 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 10:29:55AM +0200, Heiko Carstens wrote: > On Tue, Jul 03, 2018 at 10:14:49AM +0200, Peter Zijlstra wrote: > > On Mon, Jul 02, 2018 at 10:30:09PM -0400, Mathieu Desnoyers wrote: > > > > Use "get_user()". It works for 64-bit objects too, and it will be > > > > atomic in the 32-bit sub-parts on a 32-bit architecture. > > > > > > Is it really ? Last time we had this discussion, not all architectures > > > guaranteed that reading a 64-bit integer would happen in two atomic > > > 32-bit sub-parts. This was the main motivation for the LINUX_FIELD_u32_u64() > > > macro as it stands today (rather than using a union). > > > > Just state, as a requirement for supporting rseq, that the arch > > {get,put}_user(u64) on 32bit targets must be exactly 2 u32 loads/stores. > > > > We're piece-wise enabling rseq across architectures anyway, and when the > > relevant maintains do this, they can have a look at their > > {get,put}_user() implementations and fix them. > > > > If you rely on get_user(u64) working, that means microblaze is already > > broken, but I suppose it already was, since their rseq enablement patch > > is extremely dodgy. Michal? > > s390 uses the mvcos instruction to implement get_user(). That instruction > is not defined to be atomic, but may copy bytes piecemeal.. I had the > impression that the rseq fields are supposed to be updated within the > context of a single thread (user + kernel space). > > However if another user space thread is allowed to do this as well, then > the get_user() approach won't fly on s390. > > That leaves the question: does it even make sense for a thread to update > the rseq structure of a different thread? The problem is interrupts; we need interrupts on the CPU doing the store to observe either the old or the new value, not a mix. If mvcos does not guarantee that, we're having problems. Is there a reason get_user() cannot use a 'regular' load?