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=-8.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,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 8A00EC433DF for ; Wed, 13 May 2020 21:39:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7F9C32054F for ; Wed, 13 May 2020 21:39:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729302AbgEMVjN (ORCPT ); Wed, 13 May 2020 17:39:13 -0400 Received: from mga11.intel.com ([192.55.52.93]:25717 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729258AbgEMVjM (ORCPT ); Wed, 13 May 2020 17:39:12 -0400 IronPort-SDR: /WU5yRScmFdFra/taOaIl+gLPEjbArEVIaNsYZFPxSI9MscxmZDskQkahvllq2/pkmCY9g/IzK DT8uVFZbO+Jg== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 May 2020 14:39:12 -0700 IronPort-SDR: SKtTBquwr/C2Zzz7q7T9K5xYAfe+saAzgKbuNr0hJfVeMDC04/+dGR84KgNj40XKMUxPWZXcSp f7PeINpSJxRA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,389,1583222400"; d="scan'208";a="297804929" Received: from rthurerx-mobl.ger.corp.intel.com (HELO localhost) ([10.249.36.107]) by fmsmga002.fm.intel.com with ESMTP; 13 May 2020 14:39:07 -0700 Date: Thu, 14 May 2020 00:39:05 +0300 From: Jarkko Sakkinen To: "Gustavo A. R. Silva" Cc: Peter Huewe , Jason Gunthorpe , Arnd Bergmann , Greg Kroah-Hartman , linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" Subject: Re: [PATCH RESEND] tpm: eventlog: Replace zero-length array with flexible-array member Message-ID: <20200513213905.GB31974@linux.intel.com> References: <20200507040912.GA31382@embeddedor> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200507040912.GA31382@embeddedor> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On Wed, May 06, 2020 at 11:09:12PM -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] So, > the sizeof(flexible-array) can be safely removed to fix the error above. > > Lastly, prefer sizeof(*ptr) over sizeof(struct foo). > > 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