From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AIpwx4+6zrhpk2O+stj0CD2FpqGXIjdHx1AaoLIilbwexB4NSw+SJp+G5XIKccQquBY4UphhO+FV ARC-Seal: i=1; a=rsa-sha256; t=1522474496; cv=none; d=google.com; s=arc-20160816; b=WHKZZMgq+sNGTi55+02Ee5ctRXF8uaDbfevEDuUt60wxFKT5QUPck4OnLHzObZsk8U OMuxHF6aYS6eq6hzwaZk9ceKcYDbwGPUehpla+plvMIcjXDUQiRPjc5jE8/FKIdoeGa5 HIv0AoXZVG83r9SYxAjvv8rKL7rLbmMsvcREGz8sARzkgBZGofiBfOcZkyEbTpqQIuc3 /xPFiW5ZrkFp9UWK0wjWrwHXMCl5jHWl/wfegrcEZYCU/AaOnY1QIZHdTfhvkah2vm/1 rTQBiJh2CscWWFm9qlnwKQNzavve2WnufZ0b2fKLayf+BPqOSrBC7fP/iKrruXBMAlyG xiqg== 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:sender:dkim-signature :delivered-to:list-id:list-subscribe:list-unsubscribe:list-help :list-post:precedence:mailing-list:arc-authentication-results; bh=U4/9pGwXtG2foD/Qo+64uCaGI6AQqk/rAxgSrJ+dfEE=; b=R5kZVhPZHVr4g/jF44zMqLYyw/BNlwT5GPHbsCZx1O/4OPjqxQ8oLhoh/Zzp/fTlyL 7bq0mBpy6lx+jf8YrNS96bDgREdsOcIqxpsMgW4BOCgkRPtsMWGPJgAD7GskSnERS71b qot/20xaj/gGvUBT8nCUBjJFoXW3kvpY/ioeDO44pTqDC+0W2GZaxnyYB42vTMbNmdHY 7VnVCal8VTk7WKcrq1vhP6MtGhwtshd9xwZe8MawMNtP+mq9TZvvWvyKnIzs63jnCC8/ IuZkjYA74dMRhlMw9l2CKCV8Z2+rLKxQtZU34PSsP49ukqLRk5kPjM2ZW204HEbQvU16 sZ6A== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=fUQQBzNq; spf=pass (google.com: domain of kernel-hardening-return-12838-gregkh=linuxfoundation.org@lists.openwall.com designates 195.42.179.200 as permitted sender) smtp.mailfrom=kernel-hardening-return-12838-gregkh=linuxfoundation.org@lists.openwall.com Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=fUQQBzNq; spf=pass (google.com: domain of kernel-hardening-return-12838-gregkh=linuxfoundation.org@lists.openwall.com designates 195.42.179.200 as permitted sender) smtp.mailfrom=kernel-hardening-return-12838-gregkh=linuxfoundation.org@lists.openwall.com Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm List-Post: List-Help: List-Unsubscribe: List-Subscribe: Sender: Ingo Molnar Date: Sat, 31 Mar 2018 07:34:34 +0200 From: Ingo Molnar To: Kees Cook Cc: Andrew Morton , Linus Torvalds , Martin Uecker , Josh Poimboeuf , Rasmus Villemoes , Randy Dunlap , Miguel Ojeda , David Laight , Ian Abbott , LKML , Kernel Hardening Subject: Re: [PATCH v6] kernel.h: Retain constant expression output for max()/min() Message-ID: <20180331053434.akno723avvcri654@gmail.com> References: <20180326221554.GA45166@beast> <20180327054748.jx6mzywguuqfkqpv@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170609 (1.8.3) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1596040250176531135?= X-GMAIL-MSGID: =?utf-8?q?1596430217609925027?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: * Kees Cook wrote: > On Mon, Mar 26, 2018 at 10:47 PM, Ingo Molnar wrote: > > > > * Kees Cook wrote: > > > >> In the effort to remove all VLAs from the kernel[1], it is desirable to > >> build with -Wvla. However, this warning is overly pessimistic, in that > >> it is only happy with stack array sizes that are declared as constant > >> expressions, and not constant values. One case of this is the evaluation > >> of the max() macro which, due to its construction, ends up converting > >> constant expression arguments into a constant value result. > >> > >> All attempts to rewrite this macro with __builtin_constant_p() failed with > >> older compilers (e.g. gcc 4.4)[2]. However, Martin Uecker constructed[3] a > >> mind-shattering solution that works everywhere. Cthulhu fhtagn! > >> > >> This patch updates the min()/max() macros to evaluate to a constant > >> expression when called on constant expression arguments. This removes > >> several false-positive stack VLA warnings from an x86 allmodconfig > >> build when -Wvla is added: > > > > Cool! > > > > Acked-by: Ingo Molnar > > > > How many warnings are left in an allmodconfig build? > > For -Wvla? Out of the original 112 files with VLAs, 42 haven't had a > patch applied yet. Doing a linux-next allmodconfig build with the > max() patch and my latest ecc patch, we've gone from 316 warning > instances to 205. More than half of those are in > include/crypto/skcipher.h and include/crypto/hash.h. Great - once the number of warnings is zero, is the plan to enable the warning unconditionally? Thanks, Ingo