From patchwork Fri Jul 12 12:49:03 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Jarkko Sakkinen X-Patchwork-Id: 11042235 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 62F6F138D for ; Fri, 12 Jul 2019 12:49:47 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 4FA1C28A13 for ; Fri, 12 Jul 2019 12:49:47 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 3FC5B28C06; Fri, 12 Jul 2019 12:49:47 +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 B63BD28A13 for ; Fri, 12 Jul 2019 12:49:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727108AbfGLMtn (ORCPT ); Fri, 12 Jul 2019 08:49:43 -0400 Received: from mga06.intel.com ([134.134.136.31]:24366 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727045AbfGLMtm (ORCPT ); Fri, 12 Jul 2019 08:49:42 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga104.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 12 Jul 2019 05:49:42 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.63,482,1557212400"; d="scan'208";a="166672790" Received: from jroll-mobl.ger.corp.intel.com (HELO localhost) ([10.249.35.79]) by fmsmga008.fm.intel.com with ESMTP; 12 Jul 2019 05:49:39 -0700 From: Jarkko Sakkinen To: linux-kernel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-doc@vger.kernel.org Cc: tweek@google.com, matthewgarrett@google.com, jorhand@linux.microsoft.com, rdunlap@infradead.org, Jarkko Sakkinen , Jonathan Corbet , Sasha Levin Subject: [PATCH v3] tpm: Document UEFI event log quirks Date: Fri, 12 Jul 2019 15:49:03 +0300 Message-Id: <20190712124912.23630-1-jarkko.sakkinen@linux.intel.com> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP There are some weird quirks when it comes to UEFI event log. Provide a brief introduction to TPM event log mechanism and describe the quirks and how they can be sorted out. Signed-off-by: Jarkko Sakkinen --- v3: Add a section and use bullet list for references. Remove (invalid) author info. v2: Fixed one type, adjusted the last paragraph and added the file to index.rst Documentation/security/tpm/index.rst | 1 + Documentation/security/tpm/tpm_event_log.rst | 55 ++++++++++++++++++++ 2 files changed, 56 insertions(+) create mode 100644 Documentation/security/tpm/tpm_event_log.rst diff --git a/Documentation/security/tpm/index.rst b/Documentation/security/tpm/index.rst index 15783668644f..9e0815cb1e7f 100644 --- a/Documentation/security/tpm/index.rst +++ b/Documentation/security/tpm/index.rst @@ -4,5 +4,6 @@ Trusted Platform Module documentation .. toctree:: + tpm_event_log tpm_ftpm_tee tpm_vtpm_proxy diff --git a/Documentation/security/tpm/tpm_event_log.rst b/Documentation/security/tpm/tpm_event_log.rst new file mode 100644 index 000000000000..068eeb659bb9 --- /dev/null +++ b/Documentation/security/tpm/tpm_event_log.rst @@ -0,0 +1,55 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============= +TPM Event Log +============= + +This document briefly describes what TPM log is and how it is handed +over from the preboot firmware to the operating system. + +Introduction +============ + +The preboot firmware maintains an event log that gets new entries every +time something gets hashed by it to any of the PCR registers. The events +are segregated by their type and contain the value of the hashed PCR +register. Typically, the preboot firmware will hash the components to +who execution is to be handed over or actions relevant to the boot +process. + +The main application for this is remote attestation and the reason why +it is useful is nicely put in the very first section of [1]: + +"Attestation is used to provide information about the platform’s state +to a challenger. However, PCR contents are difficult to interpret; +therefore, attestation is typically more useful when the PCR contents +are accompanied by a measurement log. While not trusted on their own, +the measurement log contains a richer set of information than do the PCR +contents. The PCR contents are used to provide the validation of the +measurement log." + +UEFI event log +============== + +UEFI provided event log has a few somewhat weird quirks. + +Before calling ExitBootServices() Linux EFI stub copies the event log to +a custom configuration table defined by the stub itself. Unfortanely, +the events generated by ExitBootServices() don't end up in the table. + +The firmware provides so called final events configuration table to sort +out this issue. Events gets mirrored to this table after the first time +EFI_TCG2_PROTOCOL.GetEventLog() gets called. + +This introduces another problem: nothing guarantees that it is not called +before the Linux EFI stub gets to run. Thus, it needs to calculate and save the +final events table size while the stub is still running to the custom +configuration table so that the TPM driver can later on skip these events when +concatenating two halves of the event log from the custom configuration table +and the final events table. + +References +========== + +- [1] https://trustedcomputinggroup.org/resource/pc-client-specific-platform-firmware-profile-specification/ +- [2] The final concatenation is done in drivers/char/tpm/eventlog/efi.c