From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AG47ELvhaGHG204f9UtynziEMDPh/zeMQS81OBfg5Enog6dwPbnB2oFIOsRtVz5eP8ZpQ2YvqWEl ARC-Seal: i=1; a=rsa-sha256; t=1520532141; cv=none; d=google.com; s=arc-20160816; b=hY2cpnbhZerXkqzWX0XySDEMSLaSlSrMiy7ZAW55Yvmr48CSq0eCcHnrUKeB8hXrnS F1Q/mgaurzVnq8Lpj5RAp3sGRLr3Eqx8bcZ7Qrsq8e9l4HtyipSKCsEgkOLFK90U7t0x 5UHcId1V4cZ2J7j//6wsBcmg3PXXpSUlVgX1uaC7ULLxyO0Y80+DDeTS3NyDzLLzybpA awSKhI/2ZR6Vi1XEEpKMWi287s1aUY658IA2EfkiyhgLTmACfNeHCtZWrudc99MFggHn ISrIQEW9GCpLa4bjSavwlxeEyQxflXJRtX5QVaB49/mP2MDJ2R3klhiBlmh42LIKhGyG JCUQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=cc:to:subject:message-id:date:from:references:in-reply-to:sender :mime-version:dkim-signature:dkim-signature:delivered-to:list-id :list-subscribe:list-unsubscribe:list-help:list-post:precedence :mailing-list:arc-authentication-results; bh=JQ1FmpDMihdICwFLACLLPQxXIs2Nqp4tmPCAJEzD630=; b=Vci5SxcAwj61pXx8EHCD8QjiPGfI40qAu7T9V2AbhVOUgdP8UxpUGPy2hW9YdQy0wi 3YZIxzNhxok2TVol0enULp9O1vFYKv4PxFT5drqrWYgXzmH/vA6SwseDlRLkxC5NbEV5 F9mYrNxBkDg4ocs6ItW1VMKoVnboAXA073Lt5DZiSO00pVHNM3XHQrW+9cngZGM3aczD mRuyglKGzEziiVZ1DR3ZMUsBQJYBKnWpF8Xofz+JwBJE2rMoCFoLhFP3awU9/WsQUYPZ WO99rgDIb5+ckaOL6ql+gDBfdT+Od5/NegRasa/g9XyPh+YbFJn79sJSSLX9APjlu4qm fqKw== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=CVjPc+lg; dkim=pass header.i=@chromium.org header.s=google header.b=N1wbLMn7; spf=pass (google.com: domain of kernel-hardening-return-12245-gregkh=linuxfoundation.org@lists.openwall.com designates 195.42.179.200 as permitted sender) smtp.mailfrom=kernel-hardening-return-12245-gregkh=linuxfoundation.org@lists.openwall.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=chromium.org Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=CVjPc+lg; dkim=pass header.i=@chromium.org header.s=google header.b=N1wbLMn7; spf=pass (google.com: domain of kernel-hardening-return-12245-gregkh=linuxfoundation.org@lists.openwall.com designates 195.42.179.200 as permitted sender) smtp.mailfrom=kernel-hardening-return-12245-gregkh=linuxfoundation.org@lists.openwall.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=chromium.org Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm List-Post: List-Help: List-Unsubscribe: List-Subscribe: MIME-Version: 1.0 Sender: keescook@google.com In-Reply-To: <20180308150236.5tysfbm3xdouii5n@treble> References: <1520479847-39174-1-git-send-email-keescook@chromium.org> <20180308150236.5tysfbm3xdouii5n@treble> From: Kees Cook Date: Thu, 8 Mar 2018 10:02:01 -0800 X-Google-Sender-Auth: q16uVMIiO-ybEhlXtYIla2S-UfE Message-ID: Subject: Re: [PATCH 0/3] Remove accidental VLA usage To: Josh Poimboeuf Cc: Andrew Morton , LKML , Jonathan Corbet , "Gustavo A. R. Silva" , Steven Rostedt , 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 , "Tobin C. Harding" , Sergey Senozhatsky , Petr Mladek , Andy Shevchenko , Pantelis Antoniou , Linux Btrfs , Network Development , Kernel Hardening Content-Type: text/plain; charset="UTF-8" X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1594338745857869070?= X-GMAIL-MSGID: =?utf-8?q?1594393510616827943?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Thu, Mar 8, 2018 at 7:02 AM, Josh Poimboeuf wrote: > On Wed, Mar 07, 2018 at 07:30:44PM -0800, Kees Cook wrote: >> This series adds SIMPLE_MAX() to be used in places where a stack array >> is actually fixed, but the compiler still warns about VLA usage due to >> confusion caused by the safety checks in the max() macro. >> >> I'm sending these via -mm since that's where I've introduced SIMPLE_MAX(), >> and they should all have no operational differences. > > What if we instead simplify the max() macro's type checking so that GCC > can more easily fold the array size constants? The below patch seems to > work: Oooooh magic! Very nice. I couldn't figure out how to do this when I stared at it. Yes, let me respin. (I assume I can add your S-o-b?) -Kees > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > index 3fd291503576..ec863726da29 100644 > --- a/include/linux/kernel.h > +++ b/include/linux/kernel.h > @@ -782,42 +782,32 @@ ftrace_vprintk(const char *fmt, va_list ap) > static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { } > #endif /* CONFIG_TRACING */ > > -/* > - * min()/max()/clamp() macros that also do > - * strict type-checking.. See the > - * "unnecessary" pointer comparison. > - */ > -#define __min(t1, t2, min1, min2, x, y) ({ \ > - t1 min1 = (x); \ > - t2 min2 = (y); \ > - (void) (&min1 == &min2); \ > - min1 < min2 ? min1 : min2; }) > +extern long __error_incompatible_types_in_min_macro; > +extern long __error_incompatible_types_in_max_macro; > + > +#define __min(t1, t2, x, y) \ > + __builtin_choose_expr(__builtin_types_compatible_p(t1, t2), \ > + (t1)(x) < (t2)(y) ? (t1)(x) : (t2)(y), \ > + (t1)__error_incompatible_types_in_min_macro) > > /** > * 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) ({ \ > - t1 max1 = (x); \ > - t2 max2 = (y); \ > - (void) (&max1 == &max2); \ > - max1 > max2 ? max1 : max2; }) > +#define __max(t1, t2, x, y) \ > + __builtin_choose_expr(__builtin_types_compatible_p(t1, t2), \ > + (t1)(x) > (t2)(y) ? (t1)(x) : (t2)(y), \ > + (t1)__error_incompatible_types_in_max_macro) > > /** > * 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 +859,7 @@ 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 +867,7 @@ 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 -- Kees Cook Pixel Security