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=-11.6 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 8E84FC433DF for ; Thu, 13 Aug 2020 06:39:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 63EAB2078B for ; Thu, 13 Aug 2020 06:39:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=rasmusvillemoes.dk header.i=@rasmusvillemoes.dk header.b="ZDQ0Aoqv" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726082AbgHMGjt (ORCPT ); Thu, 13 Aug 2020 02:39:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54788 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725954AbgHMGjs (ORCPT ); Thu, 13 Aug 2020 02:39:48 -0400 Received: from mail-lj1-x244.google.com (mail-lj1-x244.google.com [IPv6:2a00:1450:4864:20::244]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7CDBEC061757 for ; Wed, 12 Aug 2020 23:39:47 -0700 (PDT) Received: by mail-lj1-x244.google.com with SMTP id v9so4954904ljk.6 for ; Wed, 12 Aug 2020 23:39:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rasmusvillemoes.dk; s=google; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=DGJizY94NWmpnKm3GAJouLUxDuyTMohNxnOXsjH4jLI=; b=ZDQ0Aoqv6FnTD3/bfGlR9gICLkiVY5WvKr3dWfAUck7qO+8DZ8teafppmock/Y4qT7 DFDnilfEVDSRSYLuy+2glK+2sknNkQlhtrXXYppwzznVaC5E6zwPYNNl9AB+GXsjvIpI yUpzwG3XoJofGSMPE4xmHuFsCDfBH2SA9srBI= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=DGJizY94NWmpnKm3GAJouLUxDuyTMohNxnOXsjH4jLI=; b=Nhi9H2kIuLe4aD49Extz4x3usmDcagGCDSEjaHH5WbIyL1h9iCm2gJGn2P05GZl9kw iUXo62AzQTQJBZATI9Zw1PvQx5suq6I2tV5q5H8Y/gh8Mu1t2EY0VFhaoDnFz6wd/K8d RN5684FelXly4Mw4pbyHscmj6s9Fv68+gVT1mkaC1rmhKzJIoEOrzlPFA4PNaz4vA9EB E9Q+lA7J7xKo5xrTSGw0En/qrcUj3Ph0HCzoQVOC43Fg4VgvLm5AwkZpMexsZ+4FG9nt NNt21xu6Her4ut9aupMp15nwyJOxHzq+r5wmIfrR1bhQ564/uC42tnCMyNv4uro2KOj+ k2Eg== X-Gm-Message-State: AOAM531Rb6w9Zw4gwWHXJyAptVKk7ze4O99+ofI2dJFltX4S2uWXdT+O z88Xcl11SE51OkEV6x/Ed6K03Q== X-Google-Smtp-Source: ABdhPJw6LZZ+Ms96aQHHbPrKTPxSWnVJUIZegwrkkTpmSBZCxYRwf6p+3bl6zuFL7Rpcoi3F+H4+qw== X-Received: by 2002:a2e:8697:: with SMTP id l23mr1231973lji.190.1597300785847; Wed, 12 Aug 2020 23:39:45 -0700 (PDT) Received: from [172.16.11.132] ([81.216.59.226]) by smtp.gmail.com with ESMTPSA id b17sm916732ljp.9.2020.08.12.23.39.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 12 Aug 2020 23:39:45 -0700 (PDT) Subject: Re: [PATCH] overflow: Add __must_check attribute to check_*() helpers To: Kees Cook , Rasmus Villemoes Cc: "Gustavo A. R. Silva" , Jason Gunthorpe , Leon Romanovsky , Matthew Wilcox , linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com References: <202008121450.405E4A3@keescook> From: Rasmus Villemoes Message-ID: Date: Thu, 13 Aug 2020 08:39:44 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <202008121450.405E4A3@keescook> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/08/2020 23.51, Kees Cook wrote: > Since the destination variable of the check_*_overflow() helpers will > contain a wrapped value on failure, it would be best to make sure callers > really did check the return result of the helper. Adjust the macros to use > a bool-wrapping static inline that is marked with __must_check. This means > the macros can continue to have their type-agnostic behavior while gaining > the function attribute (that cannot be applied directly to macros). > > Suggested-by: Rasmus Villemoes > Signed-off-by: Kees Cook > --- > include/linux/overflow.h | 51 +++++++++++++++++++++++----------------- > 1 file changed, 30 insertions(+), 21 deletions(-) > > diff --git a/include/linux/overflow.h b/include/linux/overflow.h > index 93fcef105061..ef7d538c2d08 100644 > --- a/include/linux/overflow.h > +++ b/include/linux/overflow.h > @@ -43,6 +43,16 @@ > #define is_non_negative(a) ((a) > 0 || (a) == 0) > #define is_negative(a) (!(is_non_negative(a))) > > +/* > + * Allows to effectively us apply __must_check to a macro so we can have word ordering? > + * both the type-agnostic benefits of the macros while also being able to > + * enforce that the return value is, in fact, checked. > + */ > +static inline bool __must_check __must_check_bool(bool condition) > +{ > + return unlikely(condition); > +} > + > #ifdef COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW > /* > * For simplicity and code hygiene, the fallback code below insists on > @@ -52,32 +62,32 @@ > * alias for __builtin_add_overflow, but add type checks similar to > * below. > */ > -#define check_add_overflow(a, b, d) ({ \ > +#define check_add_overflow(a, b, d) __must_check_bool(({ \ > typeof(a) __a = (a); \ > typeof(b) __b = (b); \ > typeof(d) __d = (d); \ > (void) (&__a == &__b); \ > (void) (&__a == __d); \ > __builtin_add_overflow(__a, __b, __d); \ > -}) > +})) Sorry, I meant to send this before your cooking was done but forgot about it again. Not a big deal, but it occurred to me it might be better to rename the existing check_*_overflow to __check_*_overflow (in both branches of the COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW), and then #define check_*_overflow(a, b, d) __must_check_bool(__check_*_overflow(a, b, d)) Mostly because it gives less whitespace churn, but it might also be handy to have the dunder versions available (if nothing else then perhaps in some test code). But as I said, no biggie, I'm fine either way. Now I'm just curious if 0-day is going to find some warning introduced by this :) Rasmus