From mboxrd@z Thu Jan 1 00:00:00 1970 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=-11.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 DB054C433DF for ; Wed, 13 May 2020 23:17:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F18EE2053B for ; Wed, 13 May 2020 23:17:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732548AbgEMXRk (ORCPT ); Wed, 13 May 2020 19:17:40 -0400 Received: from mga05.intel.com ([192.55.52.43]:59913 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732161AbgEMXRj (ORCPT ); Wed, 13 May 2020 19:17:39 -0400 IronPort-SDR: 5cFd2ESeM1t13rxrmZF/eEC+3XEj/3WS+NyuWAGuX3hLu2sIEGoFvpbFaUyi07Ymz+jQBBIbeM L/e6bEQ3+f0A== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 May 2020 16:17:38 -0700 IronPort-SDR: 28JTCwJ+4DmAUcv9FPKxsgcJ4jJOUzkSUj3R3Kh76MHAUCrISs355T5EXCQmbvEtAjGDpMQ/q7 lkfJJx4RUHDA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,389,1583222400"; d="scan'208";a="306922482" Received: from rthurerx-mobl.ger.corp.intel.com ([10.249.36.107]) by FMSMGA003.fm.intel.com with ESMTP; 13 May 2020 16:17:35 -0700 Message-ID: <6f7ad09530fa7491dd7a6b12f7723923544b53b4.camel@linux.intel.com> Subject: Re: [PATCH v2] tpm: eventlog: Replace zero-length array with flexible-array member From: Jarkko Sakkinen To: "Gustavo A. R. Silva" , Peter Huewe , Jason Gunthorpe , Arnd Bergmann , Greg Kroah-Hartman Cc: linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, Kees Cook Date: Thu, 14 May 2020 02:17:34 +0300 In-Reply-To: <20200508163826.GA768@embeddedor> References: <20200508163826.GA768@embeddedor> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.1-2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2020-05-08 at 11:38 -0500, Gustavo A. R. Silva wrote: > The current codebase makes use of the zero-length array language > extension to the C90 standard, but the preferred mechanism to declare > variable-length types such as these ones is a flexible array member[1][2], > introduced in C99: > > struct foo { > int stuff; > struct boo array[]; > }; > > By making use of the mechanism above, we will get a compiler warning > in case the flexible array does not occur last in the structure, which > will help us prevent some kind of undefined behavior bugs from being > inadvertently introduced[3] to the codebase from now on. > > Also, notice that, dynamic memory allocations won't be affected by > this change: > > "Flexible array members have incomplete type, and so the sizeof operator > may not be applied. As a quirk of the original implementation of > zero-length arrays, sizeof evaluates to zero."[1] > > sizeof(flexible-array-member) triggers a warning because flexible array > members have incomplete type[1]. There are some instances of code in > which the sizeof operator is being incorrectly/erroneously applied to > zero-length arrays and the result is zero. Such instances may be hiding > some bugs. So, this work (flexible-array member conversions) will also > help to get completely rid of those sorts of issues. > > Also, the following issue shows up due to the flexible-array member > having incomplete type[4]: > > drivers/char/tpm/eventlog/tpm2.c: In function ‘tpm2_bios_measurements_start’: > drivers/char/tpm/eventlog/tpm2.c:54:46: error: invalid application of ‘sizeof’ to incomplete type ‘u8[]’ {aka ‘unsigned char[]’} > 54 | size = sizeof(struct tcg_pcr_event) - sizeof(event_header->event) > | ^ > drivers/char/tpm/eventlog/tpm2.c: In function ‘tpm2_bios_measurements_next’: > drivers/char/tpm/eventlog/tpm2.c:102:10: error: invalid application of ‘sizeof’ to incomplete type ‘u8[]’ {aka ‘unsigned char[]’} > 102 | sizeof(event_header->event) + event_header->event_size; > | ^ > drivers/char/tpm/eventlog/tpm2.c: In function ‘tpm2_binary_bios_measurements_show’: > drivers/char/tpm/eventlog/tpm2.c:140:10: error: invalid application of ‘sizeof’ to incomplete type ‘u8[]’ {aka ‘unsigned char[]’} > 140 | sizeof(event_header->event) + event_header->event_size; > | ^ > scripts/Makefile.build:266: recipe for target 'drivers/char/tpm/eventlog/tpm2.o' failed > make[3]: *** [drivers/char/tpm/eventlog/tpm2.o] Error 1 > > As mentioned above: "Flexible array members have incomplete type, and > so the sizeof operator may not be applied. As a quirk of the original > implementation of zero-length arrays, sizeof evaluates to zero."[1] As > in "sizeof(event_header->event) always evaluated to 0, so removing it > has no effect". > > Lastly, make use of the struct_size() helper to deal with the > flexible array member and its host structure. > > This issue was found with the help of Coccinelle. > > [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html > [2] https://github.com/KSPP/linux/issues/21 > [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") > [4] https://github.com/KSPP/linux/issues/43 > > Signed-off-by: Gustavo A. R. Silva Reviewed-by: Jarkko Sakkinen /Jarkko > --- > Changes in v2: > - Update changelog text. > - Make use of the struct_size() helper. > > drivers/char/tpm/eventlog/tpm2.c | 12 +++++------- > include/linux/tpm_eventlog.h | 2 +- > 2 files changed, 6 insertions(+), 8 deletions(-) > > diff --git a/drivers/char/tpm/eventlog/tpm2.c b/drivers/char/tpm/eventlog/tpm2.c > index e741b1157525..37a05800980c 100644 > --- a/drivers/char/tpm/eventlog/tpm2.c > +++ b/drivers/char/tpm/eventlog/tpm2.c > @@ -51,8 +51,7 @@ static void *tpm2_bios_measurements_start(struct seq_file *m, loff_t *pos) > int i; > > event_header = addr; > - size = sizeof(struct tcg_pcr_event) - sizeof(event_header->event) > - + event_header->event_size; > + size = struct_size(event_header, event, event_header->event_size); > > if (*pos == 0) { > if (addr + size < limit) { > @@ -98,8 +97,8 @@ static void *tpm2_bios_measurements_next(struct seq_file *m, void *v, > event_header = log->bios_event_log; > > if (v == SEQ_START_TOKEN) { > - event_size = sizeof(struct tcg_pcr_event) - > - sizeof(event_header->event) + event_header->event_size; > + event_size = struct_size(event_header, event, > + event_header->event_size); > marker = event_header; > } else { > event = v; > @@ -136,9 +135,8 @@ static int tpm2_binary_bios_measurements_show(struct seq_file *m, void *v) > size_t size; > > if (v == SEQ_START_TOKEN) { > - size = sizeof(struct tcg_pcr_event) - > - sizeof(event_header->event) + event_header->event_size; > - > + size = struct_size(event_header, event, > + event_header->event_size); > temp_ptr = event_header; > > if (size > 0) > diff --git a/include/linux/tpm_eventlog.h b/include/linux/tpm_eventlog.h > index c253461b1c4e..4f8c90c93c29 100644 > --- a/include/linux/tpm_eventlog.h > +++ b/include/linux/tpm_eventlog.h > @@ -97,7 +97,7 @@ struct tcg_pcr_event { > u32 event_type; > u8 digest[20]; > u32 event_size; > - u8 event[0]; > + u8 event[]; > } __packed; > > struct tcg_event_field {