From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,LOTS_OF_MONEY, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E9B77C76190 for ; Mon, 22 Jul 2019 17:50:33 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 4DDD421901 for ; Mon, 22 Jul 2019 17:50:33 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="CXl0D6bg" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4DDD421901 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=chromium.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-16528-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 23965 invoked by uid 550); 22 Jul 2019 17:50:27 -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: Received: (qmail 23929 invoked from network); 22 Jul 2019 17:50:26 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to; bh=EydYv65e83oetehWJiFXQMJntcT2fvfp15FyorV7npo=; b=CXl0D6bgk/eTPheCyRT3F6xn5TUDB8UaUgfM2JJclOnmCyaMCzTt4LO4C+O8KJFCll 5VwB6NtqbQSCacBzC4JUL0KiVTcReEmBB75zhGCSz4MKLU6pZKrufpw6o6MMCQFDO6vX AijVsKh+7rkTYIyD+uN4sXN+goXir8D0+zVMQ= 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:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to; bh=EydYv65e83oetehWJiFXQMJntcT2fvfp15FyorV7npo=; b=fN02sHE3+ewsr/H2sNDNAq04vBuJfKGHGLObNZUrhSrYHbFU+RRdajPp7Xe4p/VSHh S25lU40G9saKFjuk0X6lZeKxmCnmPrpvnjTXFIgAg8QjpNc955NvdEsRyIBR/gDMnCc1 d1OsAXAgU/VLJx71N4CqaYwjSudxgFsqmCoEb2FvClzF5tkHoh9bnUVf8lY+SVmAMVjN /1omfFNfypRibyDXrGnDGGU6RYMf1s0iqjjOvXzEIc1k2dQ5oiN88oBcrbrGhcQQJK0t Omi3I6FyGX5dxN4h7CnqRu3roNka04yJxI9dCHpMimqjyZXGTbyaoBNccLz7AVNWYXJX 73Ng== X-Gm-Message-State: APjAAAXnenKn8GaNh1et4r7XZLVc72yBsLk7DsHjx4VrKUmLbeNeNPjC cLMrnDpmUq9UANXa152sA/IiqG2+xAk= X-Google-Smtp-Source: APXvYqw4LSNCWCxQ/yLJp59WHPmP2/0qp/JIrEN32DV882tVN30ScL0zOniDXe6YQc0xt3HY2pfVKw== X-Received: by 2002:a17:902:9a95:: with SMTP id w21mr19131904plp.126.1563817815105; Mon, 22 Jul 2019 10:50:15 -0700 (PDT) Date: Mon, 22 Jul 2019 10:50:13 -0700 From: Kees Cook To: Stephen Kitt Cc: Nitin Gote , jannh@google.com, kernel-hardening@lists.openwall.com, Joe Perches , corbet@lwn.net, linux-kernel@vger.kernel.org, Rasmus Villemoes Subject: Re: [PATCH] checkpatch: Added warnings in favor of strscpy(). Message-ID: <201907221047.4895D35B30@keescook> References: <1561722948-28289-1-git-send-email-nitin.r.gote@intel.com> <20190629181537.7d524f7d@sk2.org> <201907021024.D1C8E7B2D@keescook> <20190706144204.15652de7@heffalump.sk2.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190706144204.15652de7@heffalump.sk2.org> On Sat, Jul 06, 2019 at 02:42:04PM +0200, Stephen Kitt wrote: > On Tue, 2 Jul 2019 10:25:04 -0700, Kees Cook wrote: > > On Sat, Jun 29, 2019 at 06:15:37PM +0200, Stephen Kitt wrote: > > > On Fri, 28 Jun 2019 17:25:48 +0530, Nitin Gote > > > wrote: > > > > 1. Deprecate strcpy() in favor of strscpy(). > > > > > > This isn’t a comment “against” this patch, but something I’ve been > > > wondering recently and which raises a question about how to handle > > > strcpy’s deprecation in particular. There is still one scenario where > > > strcpy is useful: when GCC replaces it with its builtin, inline version... > > > > > > Would it be worth introducing a macro for strcpy-from-constant-string, > > > which would check that GCC’s builtin is being used (when building with > > > GCC), and fall back to strscpy otherwise? > > > > How would you suggest it operate? A separate API, or something like the > > existing overloaded strcpy() macros in string.h? > > The latter; in my mind the point is to simplify the thought process for > developers, so strscpy should be the “obvious” choice in all cases, even when > dealing with constant strings in hot paths. Something like > > __FORTIFY_INLINE ssize_t strscpy(char *dest, const char *src, size_t count) > { > size_t dest_size = __builtin_object_size(dest, 0); > size_t src_size = __builtin_object_size(src, 0); > if (__builtin_constant_p(count) && > __builtin_constant_p(src_size) && > __builtin_constant_p(dest_size) && > src_size <= count && > src_size <= dest_size && > src[src_size - 1] == '\0') { > strcpy(dest, src); > return src_size - 1; > } else { > return __strscpy(dest, src, count); > } > } > > with the current strscpy renamed to __strscpy. I imagine it’s not necessary > to tie this to FORTIFY — __OPTIMIZE__ should be sufficient, shouldn’t it? > Although building on top of the fortified strcpy is reassuring, and I might > be missing something. I’m also not sure how to deal with the backing strscpy: > weak symbol, or something else... At least there aren’t (yet) any > arch-specific implementations of strscpy to deal with, but obviously they’d > still need to be supportable. > > In my tests, this all gets optimised away, and we end up with code such as > > strscpy(raead.type, "aead", sizeof(raead.type)); > > being compiled down to > > movl $1684104545, 4(%rsp) > > on x86-64, and non-constant code being compiled down to a direct __strscpy > call. Thanks for the details! Yeah, that seems nice. I wonder if there is a sensible way to combine these also with the stracpy*() proposal[1], so the call in your example above could just be: stracpy(raead.type, "aead"); (It seems both proposals together would have the correct result...) [1] https://lkml.kernel.org/r/201907221031.8B87A9DE@keescook -- Kees Cook