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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 AA0B3C4360C for ; Wed, 25 Sep 2019 14:47:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7E13A21D7E for ; Wed, 25 Sep 2019 14:47:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2438139AbfIYOrG (ORCPT ); Wed, 25 Sep 2019 10:47:06 -0400 Received: from mga18.intel.com ([134.134.136.126]:43839 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2437125AbfIYOrG (ORCPT ); Wed, 25 Sep 2019 10:47:06 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga106.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 25 Sep 2019 07:47:05 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.64,548,1559545200"; d="scan'208";a="188798997" Received: from kmakows-mobl.ger.corp.intel.com (HELO localhost) ([10.249.39.225]) by fmsmga008.fm.intel.com with ESMTP; 25 Sep 2019 07:46:58 -0700 Date: Wed, 25 Sep 2019 17:46:57 +0300 From: Jarkko Sakkinen To: Borislav Petkov Cc: Sean Christopherson , linux-kernel@vger.kernel.org, x86@kernel.org, linux-sgx@vger.kernel.org, akpm@linux-foundation.org, dave.hansen@intel.com, nhorman@redhat.com, npmccallum@redhat.com, serge.ayoun@intel.com, shay.katz-zamir@intel.com, haitao.huang@intel.com, andriy.shevchenko@linux.intel.com, tglx@linutronix.de, kai.svahn@intel.com, josh@joshtriplett.org, luto@kernel.org, kai.huang@intel.com, rientjes@google.com, cedric.xing@intel.com Subject: Re: [PATCH v22 04/24] x86/cpu/intel: Detect SGX supprt Message-ID: <20190925144657.GA23867@linux.intel.com> References: <20190903142655.21943-1-jarkko.sakkinen@linux.intel.com> <20190903142655.21943-5-jarkko.sakkinen@linux.intel.com> <20190924161301.GI19317@zn.tnic> <20190924174311.GB16218@linux.intel.com> <20190924182119.GL19317@zn.tnic> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190924182119.GL19317@zn.tnic> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 24, 2019 at 08:21:19PM +0200, Borislav Petkov wrote: > On Tue, Sep 24, 2019 at 10:43:11AM -0700, Sean Christopherson wrote: > > The intent of running on every CPU is to verify MSR_IA32_FEATURE_CONTROL > > is correctly configured on all CPUs. It's extremely unlikely that > > firmware would misconfigure or fail to write the MSR on only APs, but if > > that does happen we'll spam dmesg and possibly panic or hang the kernel. > > > > The severity of the fallout is why we're being paranoid. KVM is similarly > > paranoid about VMX enabling since it'll BUG() on an unexpected fault due > > to a misconfigured FEATURE_CONTROL. > > None of that is in the commit message or written anywhere AFAICT. And my > crystal ball doesn't show it either so please write down properly why > this is needed. Better over the function as a comment I'd say. Added a remark: The check is done for every CPU, not just BSP, in order to verify that MSR_IA32_FEATURE_CONTROL is correctly configured on all CPUs. The other parts of the kernel, like the enclave driver, expect the same configuration from all CPUs. I think here is not necessary to go into KVM implementation details to make a case for this one. This is just a sane contract/expectation for anything using SGX and thus it is better to validate it before anything gets to use it. /Jarkko