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=-0.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED 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 1B7ECC6778A for ; Tue, 3 Jul 2018 18:10:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8190C24687 for ; Tue, 3 Jul 2018 18:10:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="qc4vZ4bi" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8190C24687 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=efficios.com 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 S934475AbeGCSJ6 (ORCPT ); Tue, 3 Jul 2018 14:09:58 -0400 Received: from mail.efficios.com ([167.114.142.138]:59268 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934195AbeGCSJy (ORCPT ); Tue, 3 Jul 2018 14:09:54 -0400 Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id 35167230DF4; Tue, 3 Jul 2018 14:09:54 -0400 (EDT) Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10032) with ESMTP id oOsCWIUQumch; Tue, 3 Jul 2018 14:09:53 -0400 (EDT) Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id A8E4F230DF1; Tue, 3 Jul 2018 14:09:53 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com A8E4F230DF1 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1530641393; bh=cBwk4tCijKrRObOxksUemWJZTxrqL+QYG7QAcwDXcE0=; h=Date:From:To:Message-ID:MIME-Version; b=qc4vZ4biiga7qoZPDx35jUvrWDpvmx7a6tK46ENaXH7NMQdRJglCfmL9cWR7/tlI+ VgdTj4/WkSV1tuxp56jLXvpXHzig8AB5I+6KtetlU9l2xZ7b6pg4ZjFATb+Pzu81gp dtQbi+tiJVyv9amcEPu8Zpcovm8Uzyjt66TeGCcUCW4KIkmWHVojWfQZst/I5OEo9c cHaqQ6xCRohemuKZjNcVyptvywWf1OwOfUuxuwzAbGJCINmAFn469K8pAkRjwz0SH0 N+lUyWCkOwpmUp2HFCOsSXtqdPghuoZXV1EPDHQ+8cMi0RNB9MX99V/Ic9pumi1Fto Bzl3s2PgsuCWw== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10026) with ESMTP id 5B_pyIxbpYNs; Tue, 3 Jul 2018 14:09:53 -0400 (EDT) Received: from mail02.efficios.com (mail02.efficios.com [167.114.142.138]) by mail.efficios.com (Postfix) with ESMTP id 89D59230DEA; Tue, 3 Jul 2018 14:09:53 -0400 (EDT) Date: Tue, 3 Jul 2018 14:09:53 -0400 (EDT) From: Mathieu Desnoyers To: Linus Torvalds Cc: Peter Zijlstra , 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 Message-ID: <775833760.11858.1530641393364.JavaMail.zimbra@efficios.com> In-Reply-To: References: <858886246.10882.1530583291379.JavaMail.zimbra@efficios.com> <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> <20180703174833.GZ2494@hirez.programming.kicks-ass.net> Subject: Re: [RFC PATCH for 4.18] rseq: use __u64 for rseq_cs fields, validate user inputs MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.142.138] X-Mailer: Zimbra 8.8.8_GA_2096 (ZimbraWebClient - FF52 (Linux)/8.8.8_GA_1703) Thread-Topic: rseq: use __u64 for rseq_cs fields, validate user inputs Thread-Index: 7hOXAcBrxoW70h0Gw8fXbspmhbEFQg== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Jul 3, 2018, at 1:59 PM, Linus Torvalds torvalds@linux-foundation.org wrote: > On Tue, Jul 3, 2018 at 10:49 AM Peter Zijlstra wrote: >> >> > 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. > > Actually, I think we should try very hard to limit even that to _just_ > the rseq pointer itself. > > Everything else can be filled in ahead of time with non-atomic stores, > and then the last thing that happens - and the only thing that wants > that final "one last atomic write" is the rseq pointer write. > > No? Well a small nit here: the rseq->rseq_cs pointer store is performed at the _very beginning_ of the rseq critical section. We indeed want that store to be performed as a single instruction by user-space. What I think you have in mind as "one last atomic write" is the commit instruction at the end of the critical section, which does not touch any field in struct rseq. > > So I'd suggest that the only part we aim to have any "atomic" behavior > at all is for the individual fields in "struct rseq" itself. So the > cpu id and the base pointer and the flags. And even they are > thread-local, so the atomicity is not about the kernel, but about user > space needing to read and update them in word-sized chunks. > > End result: absolutely nothing is atomic for the kernel. Yes, +1. If everyone is OK with that I'll go and implement the changes within the coming day. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com