From patchwork Thu Mar 8 23:37:58 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Kees Cook X-Patchwork-Id: 10269407 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 D194360594 for ; Thu, 8 Mar 2018 23:38:16 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C38AC29950 for ; Thu, 8 Mar 2018 23:38:16 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B77B929AC2; Thu, 8 Mar 2018 23:38:16 +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 9AB4329950 for ; Thu, 8 Mar 2018 23:38:15 +0000 (UTC) Received: (qmail 15624 invoked by uid 550); 8 Mar 2018 23:38:13 -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 15598 invoked from network); 8 Mar 2018 23:38:13 -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=hrGlkJyZPUh6nBPbxwRy5IRDCpqnrDZvhfL4E0wh7IQ=; b=ntcbi7D7egBkksmMA7ZMnLUimBfF+V1MMF0kPZh0CgNU16EDl0he1foT5qRw5M5Bqy CbPi9iw8KUkvuY5YeVGyvLGCzDTHs8oZ0fgIdqtNxFrbI0o3IGWKdHi6MIPnjXNDpEyp TpTIEyMdcCq4kdxCxqwLpVt1Sd8r7Xb6XjZkY= 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=hrGlkJyZPUh6nBPbxwRy5IRDCpqnrDZvhfL4E0wh7IQ=; b=L1v3A6KBcAItb3YCRko2hC9SpGDYs9FsSKP1Sprc6EGmRk7K8yhZpCaepHeD/Y6Z+4 ofB9L9cZkOu2Ur5dem2kE5v8VAuGpHbcj3wDcHU8yZVjHSd1ZQ/wsiFEaAtN5HWm2SCV LXvelHjPSUF7Nhe0+lhf5g0i6xhnnRISvuxVUafxxtXy63kWHDBRYWr+N/3vDjikNCQj 0TSrg3aQkeZ2RYxz0h2ATfxpm+Iu5Al+k9HrzbhNzsj/gEJigcQ0qSSo3Bqji24Ibp+D 8qaqYFTBBy0lV3P2v/mtxmzIsk4BH4w/ih9S59jmezpGQgipS97gQp1WVmMXwLQzf9os xITw== X-Gm-Message-State: AElRT7EF5fZByDOAQULlXyzzjm20ouNYoq2hOP+OsX2DnmqVFe6tuU+g SR/joVzaIqMfW3BIYc6A+uKulA== X-Google-Smtp-Source: AG47ELtrzOWCDwnN0OpPctutG4aNTxo8E64bNZlS92LGsH4NR0zNovQC5acgaqPJi0PNnnpmWpMKrA== X-Received: by 10.99.64.3 with SMTP id n3mr18515031pga.316.1520552280982; Thu, 08 Mar 2018 15:38:00 -0800 (PST) Date: Thu, 8 Mar 2018 15:37:58 -0800 From: Kees Cook To: Andrew Morton , linux-kernel@vger.kernel.org Cc: 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 , LKML , Kernel Hardening Subject: [PATCH v2] kernel.h: Skip single-eval logic on literals in min()/max() Message-ID: <20180308233758.GA22120@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 --- 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 | 50 ++++++++++++++++++++++++++++++++------------------ 1 file changed, 32 insertions(+), 18 deletions(-) diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 3fd291503576..108cdf7bd484 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 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) && \ + __builtin_types_compatible_p(t1, t2), \ + (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) && \ + __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 @@ -869,10 +889,7 @@ 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 +897,7 @@ 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