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=-0.8 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 58B8DC3279B for ; Tue, 3 Jul 2018 02:30:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0F6C922544 for ; Tue, 3 Jul 2018 02:30:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="JlA1AKLU" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0F6C922544 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 S1753921AbeGCCaN (ORCPT ); Mon, 2 Jul 2018 22:30:13 -0400 Received: from mail.efficios.com ([167.114.142.138]:59960 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753706AbeGCCaL (ORCPT ); Mon, 2 Jul 2018 22:30:11 -0400 Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id 459FD22FD30; Mon, 2 Jul 2018 22:30:10 -0400 (EDT) Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10032) with ESMTP id 1W68cIJ80Sih; Mon, 2 Jul 2018 22:30:09 -0400 (EDT) Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id D064522FD29; Mon, 2 Jul 2018 22:30:09 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com D064522FD29 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1530585009; bh=+KUZ1VTGTmbZBd9AREP6dWvJckviNduqiah83Zoyy8o=; h=Date:From:To:Message-ID:MIME-Version; b=JlA1AKLU5NTZYq/O3L44voykzuvmfl94WDsL267bMeX6ZxHpXln1m0IhXFmpTcC8f 9tt9C54Mv99qBLU+WP+DgtUhgjtqJaemPEMvCKM3S0otbJ6OPXfP64xLDsK8QxthCK M9diPE+EpQh8DN1r64uLcJg/B3Yyk7x05EidUOvoMLYE1oZnIIGbGOruZRUZ/BLAXL kQ38RrZgTMEEiI+VeJ2xjMhGbVQJoCLXc4fgPClDDH8/WHY8ZXb6ooVZxeiu2ucayl 2l1Nvc9nmDk4f2wXmOAVdFwjNdqaTV+oguEo9ZHPe7OhFGEyBnJngdpNtjkRgjEabh moO8IEPBngSQQ== 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 GSmUOubAJN4i; Mon, 2 Jul 2018 22:30:09 -0400 (EDT) Received: from mail02.efficios.com (mail02.efficios.com [167.114.142.138]) by mail.efficios.com (Postfix) with ESMTP id B24F022FD1F; Mon, 2 Jul 2018 22:30:09 -0400 (EDT) Date: Mon, 2 Jul 2018 22:30:09 -0400 (EDT) From: Mathieu Desnoyers To: Linus Torvalds Cc: Andy Lutomirski , Thomas Gleixner , linux-kernel , linux-api , Peter Zijlstra , "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 Message-ID: <1776351430.10902.1530585009519.JavaMail.zimbra@efficios.com> In-Reply-To: References: <20180702223143.4663-1-mathieu.desnoyers@efficios.com> <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> 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: HFYlUXtgtR1KQGyi/tBiamfT2/dVeg== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Jul 2, 2018, at 10:18 PM, Linus Torvalds torvalds@linux-foundation.org wrote: > On Mon, Jul 2, 2018 at 7:01 PM Mathieu Desnoyers > wrote: >> >> One thing to consider is how we will implement the load of that pointer >> on the kernel side. > > 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). > > Again: there is no point in trying to be atomic in the full 64 bits > (when you're running on 32-bit). The upper bits don't have to "match" > the lower bits. They just have to be zero. So doing it as two loads is > fine - the same way it's perfectly fine to do it as two stores (since > the store to the upper bits will always be zero). I'd be fine with two atomic loads, but I'd rather have a strong confirmation about this, because last time around there were architectures where it was not true as far as I recall. Thanks, Mathieu > > Linus -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com