From patchwork Fri Mar 9 20:05:36 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 10271849 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 B01A560236 for ; Fri, 9 Mar 2018 20:05:56 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id AA0ED29EF0 for ; Fri, 9 Mar 2018 20:05:56 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 9BAEA29F9E; Fri, 9 Mar 2018 20:05:56 +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 4D95C29EF0 for ; Fri, 9 Mar 2018 20:05:54 +0000 (UTC) Received: (qmail 5423 invoked by uid 550); 9 Mar 2018 20:05:52 -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 5394 invoked from network); 9 Mar 2018 20:05:51 -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=nCGDQAdSc66uVjK1QcElvBqjZ8SIGAwtKuwtBzOYP5w=; b=nhpIfFlYff0ujumC10znnKzMo6kcEaL0WNz0akPmQrBGeB2SukGZFV+CVsUbLDgodB yPQB6Wo2b5DaSQcBVQx9j75HCf+LSmiUpIM9Zn+8jak+lJL1Ar42ZN2Muiy9uVYW1V+0 rU0DpJGxsIjs3IwI3u3gJp+gXb8l5UvSTm8X0= 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=nCGDQAdSc66uVjK1QcElvBqjZ8SIGAwtKuwtBzOYP5w=; b=ZacpYoOwbg+HrmVTIAOxRqAEJ1seZe6YITZ4akZWpe0gebrJ91tpachKKMolsREYto 1Lk/d+AIRcpD/OISrRXMVem+PlEjpcHu/BQq0QHmUHHK/KmKTw2k4vE40s4O3zNyTgsN RmX4lBELktd198aGPxq2Ps6fDEaEbOXer1zP3I7XjvRnYptiwCjOsb11K+nMSDGOLo3w iuBXnFgOYSoerUTaksfUbCeegKDKK1hIs2GTUCwxD0Wm8SH/S44/4yLQoRl/Ttgh4WVo 3kRrMQ6jsALR7uepxGewtnVnUUMUQxeo5ni3327q4EMxVR4VbzE70sy4P0A6/9bs0m8Y 3yZQ== X-Gm-Message-State: APf1xPDN439EzJqcVM8NdZgFIF8o16DrkHiAD82RJUiTUrWu2ioKhL/t c8xwI32Mi4QoqQ5wtWBLS7Bzhw== X-Google-Smtp-Source: AG47ELvbTjNH1sp34W57r3yReQ4RFomEVMVy0bK0RX8FiC19kUeeFuRdk3GNmjqU538aASFyFEQsMg== X-Received: by 10.98.15.72 with SMTP id x69mr31193328pfi.16.1520625939243; Fri, 09 Mar 2018 12:05:39 -0800 (PST) Date: Fri, 9 Mar 2018 12:05:36 -0800 From: Kees Cook To: Andrew Morton Cc: linux-kernel@vger.kernel.org, Josh Poimboeuf , Rasmus Villemoes , "Gustavo A. R. Silva" , "Tobin C. Harding" , Steven Rostedt , Jonathan Corbet , 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 , Network Development , Kernel Hardening Subject: [PATCH v3] kernel.h: Skip single-eval logic on literals in min()/max() Message-ID: <20180309200536.GA5670@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 --- v3: - drop __builtin_types_compatible_p() (Rasmus, Linus) v2: - fix copy/paste-o max1_/max2_ (ijc) - clarify "compile-time" constant in comment (Rasmus) - clean up formatting on min_t()/max_t() --- include/linux/kernel.h | 48 ++++++++++++++++++++++++++++++------------------ 1 file changed, 30 insertions(+), 18 deletions(-) diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 3fd291503576..a0fca4deb3ab 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -787,37 +787,55 @@ 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 compile-time 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), \ + (t1)(x) < (t2)(y) ? (t1)(x) : (t2)(y), \ + __single_eval_min(t1, t2, \ + __UNIQUE_ID(min1_), \ + __UNIQUE_ID(min2_), \ + 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), \ + (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 @@ -869,10 +887,7 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { } * @x: first value * @y: second value */ -#define min_t(type, x, y) \ - __min(type, type, \ - __UNIQUE_ID(min1_), __UNIQUE_ID(min2_), \ - x, y) +#define min_t(type, x, y) __min(type, type, x, y) /** * max_t - return maximum of two values, using the specified type @@ -880,10 +895,7 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { } * @x: first value * @y: second value */ -#define max_t(type, x, y) \ - __max(type, type, \ - __UNIQUE_ID(min1_), __UNIQUE_ID(min2_), \ - x, y) +#define max_t(type, x, y) __max(type, type, x, y) /** * clamp_t - return a value clamped to a given range using a given type