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=-10.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 4E773C433E0 for ; Wed, 6 Jan 2021 21:24:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 047152313C for ; Wed, 6 Jan 2021 21:24:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726225AbhAFVYU (ORCPT ); Wed, 6 Jan 2021 16:24:20 -0500 Received: from mga12.intel.com ([192.55.52.136]:30030 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725815AbhAFVYU (ORCPT ); Wed, 6 Jan 2021 16:24:20 -0500 IronPort-SDR: hD3dLIJjFLYCSJ4/4ejU0QBL5/7xoPJ3ac/36HiViMy/ZPe0iqVi+k2RTiOLtBAAbAcqFy34eT mPOfjKAe2P4g== X-IronPort-AV: E=McAfee;i="6000,8403,9856"; a="156525939" X-IronPort-AV: E=Sophos;i="5.79,328,1602572400"; d="scan'208";a="156525939" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Jan 2021 13:23:39 -0800 IronPort-SDR: 05lJEBiiVneqcV8EL9Bf//Hj7fsNtf0Ij9ZvKNDPOA/shVQKzAPttNk2r/Z24CtqeUGvCz9RuT 2ILKSgXYVZOQ== X-IronPort-AV: E=Sophos;i="5.79,328,1602572400"; d="scan'208";a="422318399" Received: from jmonroe1-mobl2.amr.corp.intel.com (HELO [10.212.12.85]) ([10.212.12.85]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Jan 2021 13:23:38 -0800 Subject: Re: [RFC PATCH 11/23] x86/sgx: Add helpers to expose ECREATE and EINIT to KVM To: Sean Christopherson Cc: Kai Huang , linux-sgx@vger.kernel.org, kvm@vger.kernel.org, x86@kernel.org, jarkko@kernel.org, luto@kernel.org, haitao.huang@intel.com, pbonzini@redhat.com, bp@alien8.de, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com References: <6b29d1ee66715b40aba847b31cbdac71cbb22524.1609890536.git.kai.huang@intel.com> <863820fc-f0d2-6be6-52db-ab3eefe36f64@intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-sgx@vger.kernel.org On 1/6/21 1:04 PM, Sean Christopherson wrote: > On Wed, Jan 06, 2021, Dave Hansen wrote: >> On 1/5/21 5:56 PM, Kai Huang wrote: >>> From: Sean Christopherson >>> >>> Provide wrappers around __ecreate() and __einit() to hide the ugliness >>> of overloading the ENCLS return value to encode multiple error formats >>> in a single int. KVM will trap-and-execute ECREATE and EINIT as part >>> of SGX virtualization, and on an exception, KVM needs the trapnr so that >>> it can inject the correct fault into the guest. >> >> This is missing a bit of a step about how and why ECREATE needs to be >> run in the host in the first place. > > There's (hopefully) good info in the KVM usage patch that can be borrowed: > > Add an ECREATE handler that will be used to intercept ECREATE for the > purpose of enforcing and enclave's MISCSELECT, ATTRIBUTES and XFRM, i.e. > to allow userspace to restrict SGX features via CPUID. ECREATE will be > intercepted when any of the aforementioned masks diverges from hardware > in order to enforce the desired CPUID model, i.e. inject #GP if the > guest attempts to set a bit that hasn't been enumerated as allowed-1 in > CPUID. OK, so in plain language: the bare-metal kernel must intercept ECREATE to be able to impose policies on guests. When it does this, the bare-metal kernel runs ECREATE against the userspace mapping of the virtualized EPC. >>> diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h >>> new file mode 100644 >>> index 000000000000..0d643b985085 >>> --- /dev/null >>> +++ b/arch/x86/include/asm/sgx.h >>> @@ -0,0 +1,16 @@ >>> +/* SPDX-License-Identifier: GPL-2.0 */ >>> +#ifndef _ASM_X86_SGX_H >>> +#define _ASM_X86_SGX_H >>> + >>> +#include >>> + >>> +#ifdef CONFIG_X86_SGX_VIRTUALIZATION >>> +struct sgx_pageinfo; >>> + >>> +int sgx_virt_ecreate(struct sgx_pageinfo *pageinfo, void __user *secs, >>> + int *trapnr); >>> +int sgx_virt_einit(void __user *sigstruct, void __user *token, >>> + void __user *secs, u64 *lepubkeyhash, int *trapnr); >>> +#endif >>> + >>> +#endif /* _ASM_X86_SGX_H */ >>> diff --git a/arch/x86/kernel/cpu/sgx/virt.c b/arch/x86/kernel/cpu/sgx/virt.c >>> index d625551ccf25..4e9810ba9259 100644 >>> --- a/arch/x86/kernel/cpu/sgx/virt.c >>> +++ b/arch/x86/kernel/cpu/sgx/virt.c >>> @@ -261,3 +261,58 @@ int __init sgx_virt_epc_init(void) >>> >>> return misc_register(&sgx_virt_epc_dev); >>> } >>> + >>> +int sgx_virt_ecreate(struct sgx_pageinfo *pageinfo, void __user *secs, >>> + int *trapnr) >>> +{ >>> + int ret; >>> + >>> + __uaccess_begin(); >>> + ret = __ecreate(pageinfo, (void *)secs); >>> + __uaccess_end(); >> >> The __uaccess_begin/end() worries me. There are *very* few of these in >> the kernel and it seems like something we want to use as sparingly as >> possible. >> >> Why don't we just use the kernel mapping for 'secs' and not have to deal >> with stac/clac? > > The kernel mapping isn't readily available. Oh, duh. There's no kernel mapping for EPC... it's not RAM in the first place. > At this point, it's not even > guaranteed that @secs points at an EPC page. Unlike the driver code, where the > EPC page is allocated on-demand by the kernel, the pointer here is userspace > (technically guest) controlled. The caller (KVM) is responsible for ensuring > it's a valid userspace address, but the SGX/EPC specific checks are mostly > deferred to hardware. Ahh, got it. Kai, could we get some of this into comments or the changelog? >> I'm also just generally worried about casting away an __user without >> doing any checking. How is that OK? > > Short answer, KVM validates the virtual addresses. > > KVM validates the host virtual addresses (HVA) when creating a memslot (maps > GPA->HVA). The HVAs that are passed to these helpers are generated/retrieved > by KVM translating GVA->GPA->HVA; the GPA->HVA stage ensures the address is in a > valid memslot, and thus a valid user address. There is something a *bit* unpalatable about having KVM fill an 'unsigned long' only to cast it to a (void __user *), the to cast it back to a (void *) to pass it to the SGX inlines. I guess sparse would catch us in the window that it is __user if someone tried to dereference it. Adding access_ok()'s sounds like a good idea to me. Or, at *least* commenting why they're not necessary.