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 7361FC6778C for ; Tue, 3 Jul 2018 18:29:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2A8372416F for ; Tue, 3 Jul 2018 18:29:10 +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="RMw2NZSi" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2A8372416F 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 S934478AbeGCS3H (ORCPT ); Tue, 3 Jul 2018 14:29:07 -0400 Received: from merlin.infradead.org ([205.233.59.134]:47634 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934309AbeGCS3F (ORCPT ); Tue, 3 Jul 2018 14:29:05 -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=A02AvGlvRCLOXz68szV/oVNQj9HI/k8LTtkNgv04PDQ=; b=RMw2NZSiwZGCgsQmhmx1VlLq/ zV4/i8943bi9ZHfFvKIgrBRmj6GczM/ZT6JRCP4S7CCqBTklk/qyg26zok44ISeHXbocGjuLNa0mR UHWc0CIs0HIahj369hRJDlU9S85H04pMeCYE9N1qNjZ87BVTu/YgsfbLpCrBVFjIQwVMUPpPa9Z/v qBJVXe4YvtrhyFhwiAh6qRkXmpNFgra+ssPK+Uyrbo22W1AryCsxLJMHIAqHJ4qLaX0qrG0gqlJA5 doi56+z5fYkwM05943XG6YqkoczjwGzrPwxn+J6MWYm2f/ISKXUiAGHYRcG3z/f9r1y45jThgOVYv jjhaD9PbA==; 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 1faQ2Y-0004oL-Cq; Tue, 03 Jul 2018 18:28:38 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 1654320291063; Tue, 3 Jul 2018 20:28:37 +0200 (CEST) Date: Tue, 3 Jul 2018 20:28:37 +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: <20180703182837.GC2494@hirez.programming.kicks-ass.net> References: <858886246.10882.1530583291379.JavaMail.zimbra@efficios.com> <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> <1048940999.11846.1530640717837.JavaMail.zimbra@efficios.com> <20180703181143.GB2494@hirez.programming.kicks-ass.net> <1708848118.11868.1530641734202.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1708848118.11868.1530641734202.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 02:15:34PM -0400, Mathieu Desnoyers wrote: > ----- On Jul 3, 2018, at 2:11 PM, Peter Zijlstra peterz@infradead.org wrote: > > > On Tue, Jul 03, 2018 at 01:58:37PM -0400, Mathieu Desnoyers wrote: > >> I can modify the ABI to put the cpu_id_start and cpu_id fields inside > >> a union, and update it with a single store. > >> > >> Thoughts ? > > > > Let's keep them for now, we can always frob this later, they are aligned > > and proper, no need to expose that union to userspace. > > Isn't it weird to change the API of an exposed public uapi header ? Sure, just keep it as is. We don't need an exposed union to do a single store there. Something like the ugly below preserves API but still does a single store. But sure, if you want to expose that union for some reason, then now is the time. diff --git a/kernel/rseq.c b/kernel/rseq.c index 22b6acf1ad63..e956c48b5f83 100644 --- a/kernel/rseq.c +++ b/kernel/rseq.c @@ -85,10 +85,17 @@ static int rseq_update_cpu_id(struct task_struct *t) { u32 cpu_id = raw_smp_processor_id(); - if (__put_user(cpu_id, &t->rseq->cpu_id_start)) - return -EFAULT; - if (__put_user(cpu_id, &t->rseq->cpu_id)) + union { + struct { + u32 cpu_id_start; + u32 cpu_id; + }; + u64 val; + } x = { { .cpu_id_start = cpu_id, .cpu_id = cpu_id, } }; + + if (__put_user(x.val, (u64 *)&t->rseq->cpu_id_start)) return -EFAULT; + trace_rseq_update(t); return 0; }