From patchwork Thu Mar 8 21:40:45 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 10269265 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 3BA766037E for ; Thu, 8 Mar 2018 21:41:04 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 1E25E299C7 for ; Thu, 8 Mar 2018 21:41:04 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 1076528FB1; Thu, 8 Mar 2018 21:41:04 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.3 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.wl.linuxfoundation.org (Postfix) with SMTP id D1FEC299C7 for ; Thu, 8 Mar 2018 21:41:02 +0000 (UTC) Received: (qmail 25601 invoked by uid 550); 8 Mar 2018 21:41:00 -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 24558 invoked from network); 8 Mar 2018 21:41:00 -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 :content-transfer-encoding; bh=mXKp1jldFF0wj1CgXLNWuiL66o4SlunJLezhwmIPwLk=; b=NVYCcqt0c8y/dlWLaFZSvZ2a/KKqfBhCd532U6XsGaT73ISDHNylhLzQLC2FzUkYv9 JUA7HJZqSKOdEdDPzCVAxPi82bPjywGys2Ph42By9BhjtROkhuXiJ9/kxhf9ZCC4Ayj/ 7HG8hAmVdtGRTztfip3NanGbuz+OTeAUNUY18= 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:content-transfer-encoding; bh=mXKp1jldFF0wj1CgXLNWuiL66o4SlunJLezhwmIPwLk=; b=Yu5tnDJbPxFkzWig4XBXUlC1yZDC/5sfCABXqrq7tcDhD73ziOZeCM2lbgxDz5uo+e y6gKSP2qztmjIAzAgIcLXhn9cytVUNjOE9pqtRSZkcMrNWklT+qv+K8mzbIZJr9HEvhj 7ad0dn3HzL+8BcIf6eAckhJCc3E69rJ/Gy+Mij/CXa6XNIk2H47ymCfkoMeIFB9YhMDg lIj3zC0feh3bgKBkIc6QrfATixgGLdQIuk+24X9dHBzPAgMn+yCwQIz8XDkItas8rESk i4WTI1qUWLdkD0jAjyytSep5flUos2w13WB2QTxm65uN5SxCGpGKeLYhwCQH+ZFjyenK RnBg== X-Gm-Message-State: APf1xPDSdsnC8R8w0PtGDCrQlYTTI5aAaUD0uwwuWtBiLO3q5RkuaPY1 yA5OETfO6gQeYczwCygkh2U60A== X-Google-Smtp-Source: AG47ELsfloZncTuEy6AtA0z7gCmASS0Zq3URbPDKyQSDoVkAc984t+ECu4JPCiz3FLkuTpSZz8wj7g== X-Received: by 2002:a17:902:4601:: with SMTP id o1-v6mr25229793pld.210.1520545248540; Thu, 08 Mar 2018 13:40:48 -0800 (PST) Date: Thu, 8 Mar 2018 13:40:45 -0800 From: Kees Cook To: Andrew Morton Cc: Josh Poimboeuf , Rasmus Villemoes , "Gustavo A. R. Silva" , "Tobin C. Harding" , rostedt@goodmis.org, corbet@lwn.net, Chris Mason , Josef Bacik , David Sterba , "David S. Miller" , Alexey Kuznetsov , Hideaki YOSHIFUJI , Ingo Molnar , Peter Zijlstra , Thomas Gleixner , Masahiro Yamada , Borislav Petkov , Randy Dunlap , Ian Abbott , Sergey Senozhatsky , Petr Mladek , Andy Shevchenko , Pantelis Antoniou , linux-btrfs@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: [PATCH] kernel.h: Skip single-eval logic on literals in min()/max() Message-ID: <20180308214045.GA6787@beast> MIME-Version: 1.0 Content-Disposition: inline X-Virus-Scanned: ClamAV using ClamSMTP When max() is used in stack array size calculations from literal values (e.g. "char foo[max(sizeof(struct1), sizeof(struct2))]", the compiler thinks this is a dynamic calculation due to the single-eval logic, which is not needed in the literal case. This change removes several accidental stack VLAs from an x86 allmodconfig build: $ diff -u before.txt after.txt | grep ^- -drivers/input/touchscreen/cyttsp4_core.c:871:2: warning: ISO C90 forbids variable length array ‘ids’ [-Wvla] -fs/btrfs/tree-checker.c:344:4: warning: ISO C90 forbids variable length array ‘namebuf’ [-Wvla] -lib/vsprintf.c:747:2: warning: ISO C90 forbids variable length array ‘sym’ [-Wvla] -net/ipv4/proc.c:403:2: warning: ISO C90 forbids variable length array ‘buff’ [-Wvla] -net/ipv6/proc.c:198:2: warning: ISO C90 forbids variable length array ‘buff’ [-Wvla] -net/ipv6/proc.c:218:2: warning: ISO C90 forbids variable length array ‘buff64’ [-Wvla] Based on an earlier patch from Josh Poimboeuf. Signed-off-by: Kees Cook --- include/linux/kernel.h | 42 ++++++++++++++++++++++++++++++------------ 1 file changed, 30 insertions(+), 12 deletions(-) diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 3fd291503576..e0b39d461582 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -787,37 +787,57 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { } * strict type-checking.. See the * "unnecessary" pointer comparison. */ -#define __min(t1, t2, min1, min2, x, y) ({ \ +#define __single_eval_min(t1, t2, min1, min2, x, y) ({ \ t1 min1 = (x); \ t2 min2 = (y); \ (void) (&min1 == &min2); \ min1 < min2 ? min1 : min2; }) +/* + * In the case of builtin constant values, there is no need to do the + * double-evaluation protection, so the raw comparison can be made. + * This allows min()/max() to be used in stack array allocations and + * avoid the compiler thinking it is a dynamic value leading to an + * accidental VLA. + */ +#define __min(t1, t2, x, y) \ + __builtin_choose_expr(__builtin_constant_p(x) && \ + __builtin_constant_p(y) && \ + __builtin_types_compatible_p(t1, t2), \ + (t1)(x) < (t2)(y) ? (t1)(x) : (t2)(y), \ + __single_eval_min(t1, t2, \ + __UNIQUE_ID(max1_), \ + __UNIQUE_ID(max2_), \ + x, y)) + /** * min - return minimum of two values of the same or compatible types * @x: first value * @y: second value */ -#define min(x, y) \ - __min(typeof(x), typeof(y), \ - __UNIQUE_ID(min1_), __UNIQUE_ID(min2_), \ - x, y) +#define min(x, y) __min(typeof(x), typeof(y), x, y) -#define __max(t1, t2, max1, max2, x, y) ({ \ +#define __single_eval_max(t1, t2, max1, max2, x, y) ({ \ t1 max1 = (x); \ t2 max2 = (y); \ (void) (&max1 == &max2); \ max1 > max2 ? max1 : max2; }) +#define __max(t1, t2, x, y) \ + __builtin_choose_expr(__builtin_constant_p(x) && \ + __builtin_constant_p(y) && \ + __builtin_types_compatible_p(t1, t2), \ + (t1)(x) > (t2)(y) ? (t1)(x) : (t2)(y), \ + __single_eval_max(t1, t2, \ + __UNIQUE_ID(max1_), \ + __UNIQUE_ID(max2_), \ + x, y)) /** * max - return maximum of two values of the same or compatible types * @x: first value * @y: second value */ -#define max(x, y) \ - __max(typeof(x), typeof(y), \ - __UNIQUE_ID(max1_), __UNIQUE_ID(max2_), \ - x, y) +#define max(x, y) __max(typeof(x), typeof(y), x, y) /** * min3 - return minimum of three values @@ -871,7 +891,6 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { } */ #define min_t(type, x, y) \ __min(type, type, \ - __UNIQUE_ID(min1_), __UNIQUE_ID(min2_), \ x, y) /** @@ -882,7 +901,6 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { } */ #define max_t(type, x, y) \ __max(type, type, \ - __UNIQUE_ID(min1_), __UNIQUE_ID(min2_), \ x, y) /**