From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Desaulniers Date: Mon, 15 Oct 2018 21:53:49 +0000 Subject: Re: [PATCH] KEYS: trusted: fix -Wvarags warning Message-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit List-Id: References: <1539274203.2623.56.camel@linux.vnet.ibm.com> <20181011203126.15338-1-ndesaulniers@google.com> <0180360cfcb5458d8ff099744e8884d4@AcuMS.aculab.com> In-Reply-To: <0180360cfcb5458d8ff099744e8884d4@AcuMS.aculab.com> To: David.Laight@aculab.com Cc: "James E.J. Bottomley" , dhowells@redhat.com, Nathan Chancellor , Eric Biggers , zohar@linux.vnet.ibm.com, jmorris@namei.org, serge@hallyn.com, linux-integrity@vger.kernel.org, keyrings@vger.kernel.org, linux-security-module@vger.kernel.org, LKML On Mon, Oct 15, 2018 at 2:26 AM David Laight wrote: > > From: ndesaulniers@google.com > > Sent: 11 October 2018 21:31 > ... > > by swapping h2 and h3. > > > > security/keys/trusted.c:146:17: warning: passing an object that > > undergoes default > > argument promotion to 'va_start' has undefined behavior [-Wvarargs] > > va_start(argp, h3); > > ^ > > security/keys/trusted.c:126:37: note: parameter of type 'unsigned > > char' is declared here > > unsigned char *h2, unsigned char h3, ...) > > ^ > > Specifically, it seems that both the C90 (4.8.1.1) and C11 (7.16.1.4) > > standards explicitly call this out as undefined behavior: > > I guess that problems arise when all the arguments are stacked > and va_start/va_arg use naive pointer manipulation. > In that case &h3 might be 4n+3 aligned so va_arg() will access > misaligned stack locations. > > I doubt any modern compilers (where va_start and va_arg are builtins) > will get this 'wrong' even when all arguments are stacked. > > Seems clang is being over cautious. Yes; did you have feedback on the Denis' proposed fix, or another? > > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales) -- Thanks, ~Nick Desaulniers 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=-8.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL 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 93559C04EBB for ; Mon, 15 Oct 2018 21:54:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5548B208B3 for ; Mon, 15 Oct 2018 21:54:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="Q9xvzow8" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5548B208B3 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726978AbeJPFlI (ORCPT ); Tue, 16 Oct 2018 01:41:08 -0400 Received: from mail-pf1-f180.google.com ([209.85.210.180]:46753 "EHLO mail-pf1-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726185AbeJPFlH (ORCPT ); Tue, 16 Oct 2018 01:41:07 -0400 Received: by mail-pf1-f180.google.com with SMTP id r64-v6so10331704pfb.13 for ; Mon, 15 Oct 2018 14:54:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=9/90pkrnEVMR461DnsdHg2gnOJuyWG/ZciqdVhYl+uQ=; b=Q9xvzow8NI9z00XfehNf2cFtby3pf1Yy9smEVoO7hIqjKfMGaa8CQuEbTgwYZzpCE3 y34DuDhv/arDPmKUbmV+kLlfuXqJ2q6XFI0+KJbmGCp1hKF49g+PVXrgU4u0mIth0wod Eyzonr+YDmCFlZ/xXR0nMwqj/R7NEBaZ2UcZBQ4x59Mehj1Pe/xq0U6A3CkMgKm54PpZ oBxYLaKC52kGxOPh+XwpZfIp8PJmBqzZ2v0lIbBcqlWrS9OcRpBCOFsHPMJ0ro3Z8I8y bZAlcIuEbRSd+m7HttSDsOd1e556EgQ3JecdHzkFlCIKoAmNRej6x78ePCv/vg8PVZGl ZqpA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=9/90pkrnEVMR461DnsdHg2gnOJuyWG/ZciqdVhYl+uQ=; b=bMVh7UOuTzNoK6zI9AqXd5tvkZspX+gJYf5hMC72n1Y+ytMk/iJJOuIN5zlL/ett8P VmkFpRSUOZmxcq1SNvSjtFBwOh5bc5OBT94714eYdXvhHzkOGTGkEEFuNujE6DURztX0 fMjwCfhP8buuCF2Pt8usEj4dKMSRnc1jnrks+kOGCUJhb6tKg5l3B77DvwB5evkxl6cW 2uswA8viodw20NQHWcWcbWfXXt0A+gn1ytLffVZhgyeeSmHnPfpJ7RATMKKhDj0yUMmb fKvvVrWynaZ1vL8X0RlGjIzvI+TIk3W15YvqA+RawuRi+VkRofxw8pcVns6EVHXsnjRZ BxGA== X-Gm-Message-State: ABuFfoj11YWT334Ejp5OWAwttFFMHmHiZ7y+3ITbHw0WQbXj6mEiUcYC Yz2+lDVAUlf0LrytkKx+h5+7i3j3M3yZRrWcUvMh8Q== X-Google-Smtp-Source: ACcGV61aKdFnBLKXlf5x+dp+pN8CK8nw8Cp42aLRzZE52A1mFjfVRCmXe87LmRaOtvoT3pWkxvv5RRVthk4/Wj7j/Ug= X-Received: by 2002:a63:2f42:: with SMTP id v63-v6mr3515716pgv.202.1539640441007; Mon, 15 Oct 2018 14:54:01 -0700 (PDT) MIME-Version: 1.0 References: <1539274203.2623.56.camel@linux.vnet.ibm.com> <20181011203126.15338-1-ndesaulniers@google.com> <0180360cfcb5458d8ff099744e8884d4@AcuMS.aculab.com> In-Reply-To: <0180360cfcb5458d8ff099744e8884d4@AcuMS.aculab.com> From: Nick Desaulniers Date: Mon, 15 Oct 2018 14:53:49 -0700 Message-ID: Subject: Re: [PATCH] KEYS: trusted: fix -Wvarags warning To: David.Laight@aculab.com Cc: "James E.J. Bottomley" , dhowells@redhat.com, Nathan Chancellor , Eric Biggers , zohar@linux.vnet.ibm.com, jmorris@namei.org, serge@hallyn.com, linux-integrity@vger.kernel.org, keyrings@vger.kernel.org, linux-security-module@vger.kernel.org, LKML Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 15, 2018 at 2:26 AM David Laight wrote: > > From: ndesaulniers@google.com > > Sent: 11 October 2018 21:31 > ... > > by swapping h2 and h3. > > > > security/keys/trusted.c:146:17: warning: passing an object that > > undergoes default > > argument promotion to 'va_start' has undefined behavior [-Wvarargs] > > va_start(argp, h3); > > ^ > > security/keys/trusted.c:126:37: note: parameter of type 'unsigned > > char' is declared here > > unsigned char *h2, unsigned char h3, ...) > > ^ > > Specifically, it seems that both the C90 (4.8.1.1) and C11 (7.16.1.4) > > standards explicitly call this out as undefined behavior: > > I guess that problems arise when all the arguments are stacked > and va_start/va_arg use naive pointer manipulation. > In that case &h3 might be 4n+3 aligned so va_arg() will access > misaligned stack locations. > > I doubt any modern compilers (where va_start and va_arg are builtins) > will get this 'wrong' even when all arguments are stacked. > > Seems clang is being over cautious. Yes; did you have feedback on the Denis' proposed fix, or another? > > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales) -- Thanks, ~Nick Desaulniers