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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 615EFC636CC for ; Mon, 20 Feb 2023 10:58:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231740AbjBTK54 (ORCPT ); Mon, 20 Feb 2023 05:57:56 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52922 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231744AbjBTK5w (ORCPT ); Mon, 20 Feb 2023 05:57:52 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E708A13DD5 for ; Mon, 20 Feb 2023 02:57:32 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 3C63660DD0 for ; Mon, 20 Feb 2023 10:52:31 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 22E10C433EF; Mon, 20 Feb 2023 10:52:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1676890350; bh=WzZOQpbbHbYM0sXu2hhsAkV3nCxY0LBAS6QwJbXF9Bc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Up9sk61+6ozjTwwjc1q1wgaxWktQpnIhZ/0gfvKHVEfL8sAO3TK0iHid2lVdOOFJq KZiyeGQcU1Hg0dLvmt1gFh0F5q/g+IAt7ltVNozZPtdK4RK5g4x30G0ZVxIKf1Q2ZM rl7S3D4f8PZxri9h4D480Uvv5tPJ6pWcdSlhqmW0= Date: Mon, 20 Feb 2023 11:52:27 +0100 From: Greg KH To: KP Singh Cc: security@kernel.org, pjt@google.com, evn@google.com, jpoimboe@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, peterz@infradead.org, pawan.kumar.gupta@linux.intel.com, kim.phillips@amd.com, alexandre.chartre@oracle.com, daniel.sneddon@linux.intel.com, =?iso-8859-1?Q?Jos=E9?= Oliveira , Rodrigo Branco , Alexandra Sandulescu , Jim Mattson , stable@vger.kernel.org Subject: Re: [PATCH] x86/speculation: Fix user-mode spectre-v2 protection with KERNEL_IBRS Message-ID: References: <20230220103930.1963742-1-kpsingh@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20230220103930.1963742-1-kpsingh@kernel.org> Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Mon, Feb 20, 2023 at 11:39:30AM +0100, KP Singh wrote: > With the introduction of KERNEL_IBRS, STIBP is no longer needed > to prevent cross thread training in the kernel space. When KERNEL_IBRS > was added, it also disabled the user-mode protections for spectre_v2. > KERNEL_IBRS does not mitigate cross thread training in the userspace. > > In order to demonstrate the issue, one needs to avoid syscalls in the > victim as syscalls can shorten the window size due to > a user -> kernel -> user transition which sets the > IBRS bit when entering kernel space and clearing any training the > attacker may have done. > > Allow users to select a spectre_v2_user mitigation (STIBP always on, > opt-in via prctl) when KERNEL_IBRS is enabled. > > Reported-by: José Oliveira > Reported-by: Rodrigo Branco > Reviewed-by: Alexandra Sandulescu > Reviewed-by: Jim Mattson > Fixes: 7c693f54c873 ("x86/speculation: Add spectre_v2=ibrs option to support Kernel IBRS") > Cc: stable@vger.kernel.org > Signed-off-by: KP Singh > --- > arch/x86/kernel/cpu/bugs.c | 25 +++++++++++++++++-------- > 1 file changed, 17 insertions(+), 8 deletions(-) As this is posted publicly, there's no need to send it to security@kernel.org, it doesn't need to be involved. thanks, greg k-h