From patchwork Mon Dec 10 23:21:37 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 10722751 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 5943A17FE for ; Mon, 10 Dec 2018 23:21:59 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 442A42A710 for ; Mon, 10 Dec 2018 23:21:59 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 313ED2A71B; Mon, 10 Dec 2018 23:21:59 +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 A6A6D2A710 for ; Mon, 10 Dec 2018 23:21:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729005AbeLJXV6 (ORCPT ); Mon, 10 Dec 2018 18:21:58 -0500 Received: from mga04.intel.com ([192.55.52.120]:11277 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727852AbeLJXV6 (ORCPT ); Mon, 10 Dec 2018 18:21:58 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 10 Dec 2018 15:21:57 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,340,1539673200"; d="scan'208";a="117684766" Received: from sjchrist-coffee.jf.intel.com ([10.54.74.154]) by orsmga001.jf.intel.com with ESMTP; 10 Dec 2018 15:21:57 -0800 From: Sean Christopherson To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, Jarkko Sakkinen , Sean Christopherson , Dave Hansen , Andy Lutomirski , Peter Zijlstra Cc: "H. Peter Anvin" , linux-kernel@vger.kernel.org, linux-sgx@vger.kernel.org, Andy Lutomirski , Josh Triplett , Haitao Huang , Jethro Beekman , "Dr . Greg Wettstein" Subject: [RFC PATCH v3 0/4] x86: Add exception fixup for SGX ENCLU Date: Mon, 10 Dec 2018 15:21:37 -0800 Message-Id: <20181210232141.5425-1-sean.j.christopherson@intel.com> X-Mailer: git-send-email 2.19.2 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 This is effectively v3 of the "x86: Add vDSO exception fixup for SGX" series, but as you might of noticed, there are no vDSO changes here. Andy's comment on Spectre/retpoline[1] and Jethro's comment on making the vDSO as barebones as possible[2] got me wondering if we could let userspace dynamically set the "return" target of the SGX vDSO function, taking advantage of the fact that most (all?) SGX processes will have a single entry point for all enclaves. The initial idea was to make __vdso_sgx_enter_enclave() a barebones "function" consisting of ENCLU and UD2. SGX would provide an IOCTL via /dev/sgx that could be used to patch the UD2 in the current vDSO image to a JMP rel32, with rel32 pointing at an address provided by the user. Aside from the issues of rel32 in a 64-bit memory space, patching the vDSO image added a lot of overhead just so that the kernel could know the address of ENCLU. At that point I realized it's a hell of a lot easier to simply provide an IOCTL via /dev/sgx that allows userspace to register a per-process ENCLU exception handler. At a high level, the basic idea is the same as the vDSO approach: provide a hardcoded fixup handler for ENCLU and attempt to fixup select unhandled exceptions that occurred in user code. Pros: - No vDSO function. - Minimal userspace changes. - Smaller ABI, i.e. less bikeshedding (fingers crossed). - Kernel doesn't prevent userspace from doing stupid things, e.g. modifying the process' stack from within the enclave. - Kernel can proactively enforce the ENCLU handler as the only officialy supported ABI for enclave exception handling. Cons: - Userspace can only register a single ENCLU handler per process. - ABI is more esoteric than a standard function call. This series is based on Jarkko's current master branch, which moves all of the SGX code into arch/x86. The full code can be found here: https://github.com/sean-jc/linux/tree/2538adcece15447b988d93bf677af48073c7d219 I have not actually tested this *exact* commit beyond compiling as I do not know the health status of Jarkko's code. To test, I cherry-picked the patches into an older stable version of the code. Git was able to handle the file renaming. v1: https://lkml.kernel.org/r/20181205232012.28920-1-sean.j.christopherson@intel.com v2: https://lkml.kernel.org/r/20181206221922.31012-1-sean.j.christopherson@intel.com v3: - Replace the vDSO fixup with SGX specific fixup. - Patches 2/4 and 3/4 are essentially identical, the only difference being the name of the function that is called. The changelogs for these patches still need a lot of attention. [1] https://lkml.kernel.org/r/CALCETrVBR+2HjTqX=W4r9GOq69Xg36v4gmCKqK0wUjzAqBJnrw@mail.gmail.com [2] https://lkml.kernel.org/r/f595c046-682c-0d4a-ce68-44d4634cedf2@fortanix.com Sean Christopherson (4): x86/sgx: Add a per-mm ENCLU exception fixup handler x86/fault: Attempt to fixup unhandled #PF on ENCLU before signaling x86/traps: Attempt to fixup exceptions in vDSO before signaling x86/sgx: Add an SGX IOCTL to register a per-mm ENCLU exception handler arch/x86/include/asm/mmu.h | 4 ++++ arch/x86/include/asm/sgx.h | 13 +++++++++++++ arch/x86/include/uapi/asm/sgx.h | 23 ++++++++++++++++++----- arch/x86/kernel/cpu/sgx/driver/encl.c | 6 ++++++ arch/x86/kernel/cpu/sgx/driver/ioctl.c | 20 ++++++++++++++++++++ arch/x86/kernel/cpu/sgx/main.c | 18 ++++++++++++++++++ arch/x86/kernel/traps.c | 15 +++++++++++++++ arch/x86/mm/fault.c | 7 +++++++ 8 files changed, 101 insertions(+), 5 deletions(-)