From patchwork Fri Dec 21 23:11:36 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jarkko Sakkinen X-Patchwork-Id: 10741097 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id A1AB7161F for ; Fri, 21 Dec 2018 23:13:13 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 9088E28538 for ; Fri, 21 Dec 2018 23:13:13 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 841CD28618; Fri, 21 Dec 2018 23:13:13 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 2F08528538 for ; Fri, 21 Dec 2018 23:13:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390891AbeLUXNN (ORCPT ); Fri, 21 Dec 2018 18:13:13 -0500 Received: from mga17.intel.com ([192.55.52.151]:17555 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388956AbeLUXNM (ORCPT ); Fri, 21 Dec 2018 18:13:12 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga107.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 21 Dec 2018 15:13:12 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,383,1539673200"; d="scan'208";a="120338312" Received: from ncanderx-mobl.ger.corp.intel.com (HELO localhost) ([10.249.254.238]) by FMSMGA003.fm.intel.com with ESMTP; 21 Dec 2018 15:13:03 -0800 From: Jarkko Sakkinen To: x86@kernel.org, linux-sgx@vger.kernel.org Cc: akpm@linux-foundation.org, dave.hansen@intel.com, sean.j.christopherson@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, bp@alien8.de, josh@joshtriplett.org, luto@kernel.org, Andy Lutomirski , Dave Hansen , Jarkko Sakkinen Subject: [PATCH v18 07/25] x86/mm: x86/sgx: Signal SIGSEGV for userspace #PFs w/ PF_SGX Date: Sat, 22 Dec 2018 01:11:36 +0200 Message-Id: <20181221231154.6120-8-jarkko.sakkinen@linux.intel.com> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20181221231154.6120-1-jarkko.sakkinen@linux.intel.com> References: <20181221231154.6120-1-jarkko.sakkinen@linux.intel.com> MIME-Version: 1.0 Sender: linux-sgx-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-sgx@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Sean Christopherson The PF_SGX bit is set if and only if the #PF is detected by the SGX Enclave Page Cache Map (EPCM). The EPCM is a hardware-managed table that enforces accesses to an enclave's EPC pages in addition to the software-managed kernel page tables, i.e. the effective permissions for an EPC page are a logical AND of the kernel's page tables and the corresponding EPCM entry. The EPCM is consulted only after an access walks the kernel's page tables, i.e.: a. the access was allowed by the kernel b. the kernel's tables have become less restrictive than the EPCM c. the kernel cannot fixup the cause of the fault Noteably, (b) implies that either the kernel has botched the EPC mappings or the EPCM has been invalidated (see below). Regardless of why the fault occurred, userspace needs to be alerted so that it can take appropriate action, e.g. restart the enclave. This is reinforced by (c) as the kernel doesn't really have any other reasonable option, i.e. signalling SIGSEGV is actually the least severe action possible. Although the primary purpose of the EPCM is to prevent a malicious or compromised kernel from attacking an enclave, e.g. by modifying the enclave's page tables, do not WARN on a #PF w/ PF_SGX set. The SGX architecture effectively allows the CPU to invalidate all EPCM entries at will and requires that software be prepared to handle an EPCM fault at any time. The architecture defines this behavior because the EPCM is encrypted with an ephemeral key that isn't exposed to software. As such, the EPCM entries cannot be preserved across transitions that result in a new key being used, e.g. CPU power down as part of an S3 transition or when a VM is live migrated to a new physical system. Cc: Andy Lutomirski Cc: Dave Hansen Signed-off-by: Sean Christopherson Signed-off-by: Jarkko Sakkinen --- arch/x86/mm/fault.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 71d4b9d4d43f..eb8db2425b5b 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -1108,6 +1108,19 @@ access_error(unsigned long error_code, struct vm_area_struct *vma) if (error_code & X86_PF_PK) return 1; + /* + * Access is blocked by the Enclave Page Cache Map (EPCM), i.e. the + * access is allowed by the PTE but not the EPCM. This usually happens + * when the EPCM is yanked out from under us, e.g. by hardware after a + * suspend/resume cycle. In any case, software, i.e. the kernel, can't + * fix the source of the fault as the EPCM can't be directly modified + * by software. Handle the fault as an access error in order to signal + * userspace, e.g. so that userspace can rebuild their enclave(s), even + * though userspace may not have actually violated access permissions. + */ + if (unlikely(error_code & X86_PF_SGX)) + return 1; + /* * Make sure to check the VMA so that we do not perform * faults just to hit a X86_PF_PK as soon as we fill in a