From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AG47ELs1eMzBEToB7mVsF6SLE44++IWNDiQ1AeowYebLbHsyBGq2bhgDx9qW6ZwuRPFED/RtWaGT ARC-Seal: i=1; a=rsa-sha256; t=1520532735; cv=none; d=google.com; s=arc-20160816; b=NKGXC6Eas0xU3pEatoa5dztXYIeuQRvjEOnUmeEeoJwt1u+GarkBN3B0hMo5jyN6s8 IgSNy/gxZN7cNt8DrhAVwyB22nFJn655H7gV1XRZuqpN48EN5Qc0tiHaZFJ8wN3ktrUA ljBxxRkpj2pXZcAkP/AQ+A/CIAIM4XrB/8P+KtBIKwR7hF47zWGm5X54fQ8/X74bdy6R 6JNHG6/LXoP3OEmHcvHoc9pg/TVaUJcPGjPM7nL46Q0JZIxFLixEmNZKF3nBb0+BT2cB ooqBQQlggm8j8Y6EhXdzuGN6RFTGu7kl+GTmXUnb4BGwiZ9/avdU6dkEvbzH1th5bSvi mxtg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date:delivered-to:list-id :list-subscribe:list-unsubscribe:list-help:list-post:precedence :mailing-list:arc-authentication-results; bh=35bzQ8nB9g+srnhSEGDkvtn0S/KCubQzPlD/bWQYqCk=; b=PpF1W1Gu8PibBWU4rLfoUMUU4Ql/6CSptaotaHuExS7iVLd58iZtP8YGsD6NU8I6bO gcpoziwtl/rD53BCqFReHEE0Q4VD6y7oIKRLclj2MdEE6ySnRTx5hJPcMQ+RJCquHt+m laYSsTvmGq8Xwd+AVthNDpFgZByymC7OMLEyAhRoa0lQWomc3QJkYpGNP7cqUrEKq1z8 SHvweSfWTXVticRbEgknUkmElORIKo3lNMmgROlJxrtCW2knAIdxyl0IHPqYI9h5b6cN BLv8v/EUuyNXlDS6Qb2LlRPBsB0HAqprzLlcozzxGa7puBNgmI2K1eWNg66jMcElXyAF gTcg== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of kernel-hardening-return-12246-gregkh=linuxfoundation.org@lists.openwall.com designates 195.42.179.200 as permitted sender) smtp.mailfrom=kernel-hardening-return-12246-gregkh=linuxfoundation.org@lists.openwall.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=redhat.com Authentication-Results: mx.google.com; spf=pass (google.com: domain of kernel-hardening-return-12246-gregkh=linuxfoundation.org@lists.openwall.com designates 195.42.179.200 as permitted sender) smtp.mailfrom=kernel-hardening-return-12246-gregkh=linuxfoundation.org@lists.openwall.com; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=redhat.com Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm List-Post: List-Help: List-Unsubscribe: List-Subscribe: Date: Thu, 8 Mar 2018 12:11:54 -0600 From: Josh Poimboeuf To: Kees Cook 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 Subject: Re: [PATCH 0/3] Remove accidental VLA usage Message-ID: <20180308181154.z2pipjykwos2mpzs@treble> References: <1520479847-39174-1-git-send-email-keescook@chromium.org> <20180308150236.5tysfbm3xdouii5n@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.6.0.1 (2016-04-01) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1594338745857869070?= X-GMAIL-MSGID: =?utf-8?q?1594394133961598386?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Thu, Mar 08, 2018 at 10:02:01AM -0800, Kees Cook wrote: > 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?) I'm going to be traveling for a few days, so I bequeath the patch to you. You can add my SOB. I agree with Steve's suggestion to run it through 0-day. > > -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 -- Josh