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=-4.0 required=3.0 tests=INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_PASS 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 3EEDEC43441 for ; Tue, 27 Nov 2018 22:07:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 01AC22147D for ; Tue, 27 Nov 2018 22:07:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 01AC22147D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.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 S1726855AbeK1JGi (ORCPT ); Wed, 28 Nov 2018 04:06:38 -0500 Received: from mx2.suse.de ([195.135.220.15]:53530 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726299AbeK1JGh (ORCPT ); Wed, 28 Nov 2018 04:06:37 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 2D0E6ACDE; Tue, 27 Nov 2018 22:07:17 +0000 (UTC) Date: Tue, 27 Nov 2018 23:07:15 +0100 (CET) From: Jiri Kosina To: Thomas Gleixner cc: Tim Chen , Ingo Molnar , LKML , x86@kernel.org, Peter Zijlstra , Andy Lutomirski , Linus Torvalds , Tom Lendacky , Josh Poimboeuf , Andrea Arcangeli , David Woodhouse , Andi Kleen , Dave Hansen , Casey Schaufler , Asit Mallick , Arjan van de Ven , Jon Masters , Waiman Long , Greg KH , Dave Stewart , Kees Cook Subject: Re: [patch 20/24] x86/speculation: Split out TIF update In-Reply-To: Message-ID: References: <20181121201430.559770965@linutronix.de> <20181121201724.227260385@linutronix.de> <20181123073735.GA12959@gmail.com> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 27 Nov 2018, Thomas Gleixner wrote: > > static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl) > > diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c > > index 3f5e351bdd37..6c4fcef52b19 100644 > > --- a/arch/x86/kernel/process.c > > +++ b/arch/x86/kernel/process.c > > @@ -474,6 +474,21 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p) > > > > tifn = READ_ONCE(task_thread_info(next_p)->flags); > > tifp = READ_ONCE(task_thread_info(prev_p)->flags); > > + > > + /* > > + * SECCOMP tasks might have had their spec_ctrl flags updated during > > + * runtime from a different CPU. > > + * > > + * When switching to such a task, populate thread flags with the ones > > + * that have been temporarily saved in spec_flags by task_update_spec_tif() > > + * in order to make sure MSR value is always kept up to date. > > + * > > + * SECCOMP tasks never disable the mitigation for other threads, only enable. > > + */ > > + if (IS_ENABLED(CONFIG_SECCOMP) && > > + test_and_clear_tsk_thread_flag(next_p, TIF_SPEC_UPDATE)) > > + tifp |= READ_ONCE(task_thread_info(next_p)->spec_flags); > > And how does that get folded into task_thread_info(next_p)->flags for the > next context switch? Does it really have to? We need this special handling only if the next task has TIF_SPEC_UPDATE set, which is one-off event globally (when seccomp marks all its threads so due to seccomp filter change), and once all the TIF_SPEC_UPDATE tasks schedule at least once, we're in a consistent state again and don't need this, as every running task will then have its TIF consistent with MSR value. Thanks, -- Jiri Kosina SUSE Labs