From patchwork Fri Jun 5 14:21:59 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Fabian Vogt X-Patchwork-Id: 206304 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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED 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 46EA3C433E0 for ; Fri, 5 Jun 2020 14:22:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 28363206DC for ; Fri, 5 Jun 2020 14:22:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728727AbgFEOWE (ORCPT ); Fri, 5 Jun 2020 10:22:04 -0400 Received: from mx2.suse.de ([195.135.220.15]:46040 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728330AbgFEOWC (ORCPT ); Fri, 5 Jun 2020 10:22:02 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 48E3FAEC8; Fri, 5 Jun 2020 14:22:04 +0000 (UTC) From: Fabian Vogt To: linux-efi Cc: Ard Biesheuvel , "Lee, Chun-Yi" , =?iso-8859-1?q?Lo=EFc?= Yhuel , Matthew Garrett , Jarkko Sakkinen Subject: [PATCH] tpm: verify that it's actually an event log header before parsing Date: Fri, 05 Jun 2020 16:21:59 +0200 Message-ID: <1894249.ujS34B1uSo@linux-e202.suse.de> MIME-Version: 1.0 Sender: linux-efi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-efi@vger.kernel.org It's possible that the first event in the log is not actually a log header at all, but rather a normal event. This leads to the cast in __calc_tpm2_event_size being an invalid conversion, which means that the values read are effectively garbage. Depending on the first event's contents, this leads either to apparently normal behaviour, a crash or a freeze. While this behaviour of the firmware is not in accordance with the TCG Client EFI Specification, this happens on a Dell Precision 5510 with the TPM enabled but hidden from the OS ("TPM On" disabled, state otherwise untouched). The EFI claims that the TPM is present and active and supports the TCG 2.0 event log format. Fortunately, this can be worked around by simply checking the header of the first event and the event log header signature itself. Commit b4f1874c6216 ("tpm: check event log version before reading final events") addressed a similar issue also found on Dell models. Fixes: 6b0326190205 ("efi: Attempt to get the TCG2 event log in the boot stub") Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1165773 Signed-off-by: Fabian Vogt --- include/linux/tpm_eventlog.h | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/include/linux/tpm_eventlog.h b/include/linux/tpm_eventlog.h index 4f8c90c93c29..b913faeedcb5 100644 --- a/include/linux/tpm_eventlog.h +++ b/include/linux/tpm_eventlog.h @@ -81,6 +81,8 @@ struct tcg_efi_specid_event_algs { u16 digest_size; } __packed; +#define TCG_SPECID_SIG "Spec ID Event03" + struct tcg_efi_specid_event_head { u8 signature[16]; u32 platform_class; @@ -171,6 +173,7 @@ static inline int __calc_tpm2_event_size(struct tcg_pcr_event2_head *event, int i; int j; u32 count, event_type; + const u8 zero_digest[sizeof(event_header->digest)] = {0}; marker = event; marker_start = marker; @@ -198,10 +201,19 @@ static inline int __calc_tpm2_event_size(struct tcg_pcr_event2_head *event, count = READ_ONCE(event->count); event_type = READ_ONCE(event->event_type); + /* Verify that it's the log header */ + if (READ_ONCE(event_header->pcr_idx) != 0 || + READ_ONCE(event_header->event_type) != NO_ACTION || + memcmp(event_header->digest, zero_digest, sizeof(zero_digest))) { + size = 0; + goto out; + } + efispecid = (struct tcg_efi_specid_event_head *)event_header->event; /* Check if event is malformed. */ - if (count > efispecid->num_algs) { + if (memcmp(efispecid->signature, TCG_SPECID_SIG, + sizeof(TCG_SPECID_SIG)) || count > efispecid->num_algs) { size = 0; goto out; }