From patchwork Sat Dec 11 15:33:20 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jarkko Sakkinen X-Patchwork-Id: 12671819 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 28074C433F5 for ; Sat, 11 Dec 2021 15:33:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231302AbhLKPde (ORCPT ); Sat, 11 Dec 2021 10:33:34 -0500 Received: from sin.source.kernel.org ([145.40.73.55]:52910 "EHLO sin.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229836AbhLKPde (ORCPT ); Sat, 11 Dec 2021 10:33:34 -0500 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 sin.source.kernel.org (Postfix) with ESMTPS id A7264CE0955; Sat, 11 Dec 2021 15:33:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 232C1C004DD; Sat, 11 Dec 2021 15:33:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1639236810; bh=rM8KSxLDKIm9uW4S8GMq6JH5JdBGz8KBbko7xHOzWCQ=; h=From:To:Cc:Subject:Date:From; b=mo0/ikL0uo98UzoWu44jo33ad1TbCyVGtAWUbL676XiwSDlh2zjO3Y0BZgr7JsicZ u+mfWL0M5e/NgZr7/n0juppDxY38zF7PGX7xkjepL9YLKawSXE3CYqRAvXyBeDqmpr n/HexAlpp7CLtJO3f6UVA/189uJifijmVDethRhi10qjvPzcJorEtIlU8RkzqR4Z4v P+M5IV09h1X8ay0PICi1heTClLNQeXMdWXaGJk6avtnVRRcDSToRd/dYjb+G1LVdfW lT+/IJnw2xTrEN30v0nzvOapvP2h7yaUhW40xJ4i0+F+8b5YAjuTyU9GvozLjqv1sH zq2FPaGaRW0cQ== From: Jarkko Sakkinen To: Michael Kerrisk Cc: linux-man@vger.kernel.org, linux-sgx@vger.kernel.org, Dave Hansen , nathaniel@profian.com, Reinette Chatre , Jarkko Sakkinen Subject: [PATCH v11] sgx.7: New page with overview of Software Guard eXtensions (SGX) Date: Sat, 11 Dec 2021 17:33:20 +0200 Message-Id: <20211211153320.17438-1-jarkko@kernel.org> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-sgx@vger.kernel.org Signed-off-by: Jarkko Sakkinen --- v11: * Address Reinette's remarks for v10: https://lore.kernel.org/linux-sgx/8f84b8e8-b478-bb81-4aa8-536df882a144@intel.com/ v10: * v9 was malformed, essentially a resend. v9: * Rename "Address Space" section as "Memory mapping", and refine the text. * Rename "Ioctls" section as "Construction", and refine the text. v8: * Fix errors reported for the previous version. v7: * Added more meat about the address space and API. * Reorganized the text to have focus more on developer to have a big picture of kernel provided interfaces. v6: * Small fixes based on Dave's and Reinette's feedback. * Extended the "Permissions" section to cover mmap() v5: * Taking away hardware concepts and focusing more on the interface. v4: * Did a heavy edit trying to streamline the story a bit and focus on stuff important to the user (e.g. lighten up x86 details). v3: * Overhaul based on Michael's comments. Most likely needs to be refined in various places but this is at least a small step forward for sure. v2: * Fixed the semantic newlines convention and various style errors etc. that were reported by Alenjandro and Michael. * SGX was merged to v5. --- man7/sgx.7 | 146 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 146 insertions(+) create mode 100644 man7/sgx.7 diff --git a/man7/sgx.7 b/man7/sgx.7 new file mode 100644 index 000000000..0b5aa87e9 --- /dev/null +++ b/man7/sgx.7 @@ -0,0 +1,146 @@ +.\" Copyright (C) 2021 Intel Corporation +.\" +.\" %%%LICENSE_START(VERBATIM) +.\" Permission is granted to make and distribute verbatim copies of this +.\" manual provided the copyright notice and this permission notice are +.\" preserved on all copies. +.\" +.\" Permission is granted to copy and distribute modified versions of this +.\" manual under the conditions for verbatim copying, provided that the +.\" entire resulting derived work is distributed under the terms of a +.\" permission notice identical to this one. +.\" +.\" Since the Linux kernel and libraries are constantly changing, this +.\" manual page may be incorrect or out-of-date. The author(s) assume no +.\" responsibility for errors or omissions, or for damages resulting from +.\" the use of the information contained herein. The author(s) may not +.\" have taken the same level of care in the production of this manual, +.\" which is licensed free of charge, as they might when working +.\" professionally. +.\" +.\" Formatted or processed versions of this manual, if unaccompanied by +.\" the source, must acknowledge the copyright and authors of this work. +.\" %%%LICENSE_END +.\" +.TH SGX 7 2021\-02\-02 "Linux" "Linux Programmer's Manual" +.PP +sgx - overview of Software Guard eXtensions +.SH SYNOPSIS +.EX +.B #include +.PP +.IB enclave " = open(""/dev/sgx_enclave"", O_RDWR);" +.EE +.SH DESCRIPTION +Intel Software Guard eXtensions (SGX) allow applications to host +enclaves, +protected executable objects in memory. +.PP +Enclaves are blobs of executable code, +running inside a CPU enforced container, +which is mapped to the process address space. +They are represented as the instances of +.IR /dev/sgx_enclave . +They have a fixed set of entry points, +defined when the enclave is built. +.PP +SGX can only be available if the kernel is configured and built with the +.B CONFIG_X86_SGX +option. +If CPU, BIOS and kernel have SGX enabled, +.I sgx +appears in the +.I flags +field of +.IR /proc/cpuinfo . +.PP +If SGX appears not to be available, +ensure that SGX is enabled in the BIOS. +If a BIOS presents a choice between +.I Enabled +and +.I Software Enabled +modes for SGX, +choose +.IR Enabled . +.PP +.SS Memory mapping +The file descriptor for an enclave can be shared among multiple processes. +An enclave is required by the CPU to be placed to an address, +which is a multiple of its size. +An address range containing a reasonable base address can be probed with an anonymous +.BR mmap(2) +call: +.PP +.EX +void *area = mmap(NULL, size * 2, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, + -1, 0); + +void *base = ((uint64_t)area + size - 1) & ~(size - 1); +.EE +.PP +The enclave file descriptor itself can be then mapped with the +.BR MAP_FIXED +flag set to the carved out memory. +.SS Construction +An enclave instance is created by opening +.IR /dev/sgx_enclave . +Its contents are populated with the +.BR ioctl (2) +interface in +.IR : +.TP +.IB SGX_IOC_ENCLAVE_CREATE +Create SGX Enclave Control Structure (SECS) for the enclave. +SECS is a hardware defined structure, +which contains the global properties of an enclave. +.IB SGX_IOC_ENCLAVE_CREATE +is a one-shot call that fixes the enclave's address and +size for the rest of its life-cycle. +.TP +.IB SGX_IOC_ENCLAVE_ADD_PAGES +Fill a range of the enclave's pages with the caller provided data and protection bits. +Memory mappings of the enclave can only set protection bits that are defined in this ioctl. +The pages added are either regular pages for code and data, +or thread control structures (TCS). +The latter define the entry points to the enclave, +which can be entered after the initialization. +.TP +.IB SGX_IOC_ENCLAVE_INIT +Initialize the enclave for the run-time. +After a successful initialization, +no new pages can be added to the enclave. +.SS Invocation +Thread control structure (TCS) pages are the entry points to the enclave, +which further define an offset inside the enclave where the execution begins. +The entry points are invoked with +.IR __vdso_sgx_enter_enclave . +The prototype for the vDSO is defined by +.BR vdso_sgx_enter_enclave_t +in +.IR . +.SS Permissions +.PP +During the build process each enclave page is assigned protection bits, +as part of +.BR ioctl(SGX_IOC_ENCLAVE_ADD_PAGES). +These protections are also the maximum protections with which the page can be be mapped. +If +.BR mmap (2) +is called with higher protections than those defined during the build, +it will return +.B -EACCES. +If +.BR ioctl(SGX_IOC_ENCLAVE_ADD_PAGES) +is called after +.BR mmap (2) +with lower protections, +the caller receives +.BR SIGBUS, +once it accesses the page for the first time. +.SH VERSIONS +The SGX feature was added in Linux 5.11. +.SH SEE ALSO +.BR ioctl (2), +.BR mmap (2), +.BR mprotect (2)