From patchwork Sat Aug 15 17:09:24 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 11715543 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 7DBE613B1 for ; Sat, 15 Aug 2020 17:09:41 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id DA3FE23B30 for ; Sat, 15 Aug 2020 17:09:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="CI1KLRx+" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DA3FE23B30 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=chromium.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-19635-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com Received: (qmail 20073 invoked by uid 550); 15 Aug 2020 17:09:39 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 20047 invoked from network); 15 Aug 2020 17:09:38 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:mime-version:content-disposition; bh=soE2IFby27f3lT1vJqM47DLs36Y61YrsYS5+tpHeZ7Q=; b=CI1KLRx+27luHuKs2XaeFptA0WMQW5Fz18CFhEPtVnkbVKV5k7fBMYmRMvP9FuTb7i POd83LEdDrPoRKUNpQJZiUqmb1YMxIu3WAyCVpW3k18G+SD1Q3iGNo/NWnt2drExn+vL j+P0BkgpDOAq7PVGoXtJGBjyX9cFgRCgT2DA0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:mime-version :content-disposition; bh=soE2IFby27f3lT1vJqM47DLs36Y61YrsYS5+tpHeZ7Q=; b=mVWJfGJl+sep6RuKE7ZHXBQ+g/dMzkQ6Eh7SiMNFO/gga4pHMYIKZaDbOsrscSkbj6 /ibiFPAN4RdtcO9wF05urkg75D8482CPjz2FOTmi6YUSi+ouHtSh67RpdGJpTJTHyyDi Lu3hNbKTJgkRujP3aFNQZ5KgtrlyQF2jRlY/vfXRx04SUOgxJWiOrOD6UR5Nr5tYcvsM UQg6tGCp0Rs6OBCniAeyDMEv3NYgJWrAWSkOUvzD83zK45gZU26sq4yCSgEsey4lq3/9 awMDbNW0E2hHt1DQf/rTWApy3RxkLdLLvFpAlxQtjmgzIsAIpl8mVlDSZ8Em6777HzY7 sGBQ== X-Gm-Message-State: AOAM533YnFoGygy7vf5gah1vwhMsMqzwDrPN55UK7UOyzAm65/CU00+r gUGWEqMp5xHenflsgwdkgSg1rw== X-Google-Smtp-Source: ABdhPJw++rQdsQjQ+F1CYSDJTNwjmrCJstNOaRhqVrb+4iAk5WeYCFnuaK3T5187FLXs3/JeJ8ejCw== X-Received: by 2002:a17:902:9a06:: with SMTP id v6mr6020983plp.57.1597511366548; Sat, 15 Aug 2020 10:09:26 -0700 (PDT) Date: Sat, 15 Aug 2020 10:09:24 -0700 From: Kees Cook To: Rasmus Villemoes Cc: "Gustavo A. R. Silva" , Jason Gunthorpe , Leon Romanovsky , Matthew Wilcox , linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: [PATCH v2] overflow: Add __must_check attribute to check_*() helpers Message-ID: <202008151007.EF679DF@keescook> MIME-Version: 1.0 Content-Disposition: inline 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 --- v2: - de-generalized __must_check_overflow() from being named "bool" (willy) - fix comment typos (rasmus) v1: https://lore.kernel.org/lkml/202008121450.405E4A3@keescook --- include/linux/overflow.h | 39 ++++++++++++++++++++++++--------------- 1 file changed, 24 insertions(+), 15 deletions(-) diff --git a/include/linux/overflow.h b/include/linux/overflow.h index 93fcef105061..f1c4e7b56bd9 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 for effectively applying __must_check to a macro so we can have + * 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_overflow(bool overflow) +{ + return unlikely(overflow); +} + #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_overflow(({ \ typeof(a) __a = (a); \ typeof(b) __b = (b); \ typeof(d) __d = (d); \ (void) (&__a == &__b); \ (void) (&__a == __d); \ __builtin_add_overflow(__a, __b, __d); \ -}) +})) -#define check_sub_overflow(a, b, d) ({ \ +#define check_sub_overflow(a, b, d) __must_check_overflow(({ \ typeof(a) __a = (a); \ typeof(b) __b = (b); \ typeof(d) __d = (d); \ (void) (&__a == &__b); \ (void) (&__a == __d); \ __builtin_sub_overflow(__a, __b, __d); \ -}) +})) -#define check_mul_overflow(a, b, d) ({ \ +#define check_mul_overflow(a, b, d) __must_check_overflow(({ \ typeof(a) __a = (a); \ typeof(b) __b = (b); \ typeof(d) __d = (d); \ (void) (&__a == &__b); \ (void) (&__a == __d); \ __builtin_mul_overflow(__a, __b, __d); \ -}) +})) #else @@ -190,21 +200,20 @@ }) -#define check_add_overflow(a, b, d) \ +#define check_add_overflow(a, b, d) __must_check_overflow( \ __builtin_choose_expr(is_signed_type(typeof(a)), \ __signed_add_overflow(a, b, d), \ - __unsigned_add_overflow(a, b, d)) + __unsigned_add_overflow(a, b, d))) -#define check_sub_overflow(a, b, d) \ +#define check_sub_overflow(a, b, d) __must_check_overflow( \ __builtin_choose_expr(is_signed_type(typeof(a)), \ __signed_sub_overflow(a, b, d), \ - __unsigned_sub_overflow(a, b, d)) + __unsigned_sub_overflow(a, b, d))) -#define check_mul_overflow(a, b, d) \ +#define check_mul_overflow(a, b, d) __must_check_overflow( \ __builtin_choose_expr(is_signed_type(typeof(a)), \ __signed_mul_overflow(a, b, d), \ - __unsigned_mul_overflow(a, b, d)) - + __unsigned_mul_overflow(a, b, d))) #endif /* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */ @@ -227,7 +236,7 @@ * '*d' will hold the results of the attempted shift, but is not * considered "safe for use" if false is returned. */ -#define check_shl_overflow(a, s, d) ({ \ +#define check_shl_overflow(a, s, d) __must_check_overflow(({ \ typeof(a) _a = a; \ typeof(s) _s = s; \ typeof(d) _d = d; \ @@ -237,7 +246,7 @@ *_d = (_a_full << _to_shift); \ (_to_shift != _s || is_negative(*_d) || is_negative(_a) || \ (*_d >> _to_shift) != _a); \ -}) +})) /** * array_size() - Calculate size of 2-dimensional array.