From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8D133199E88; Thu, 6 Mar 2025 06:12:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741241571; cv=none; b=RoT+c+iLrG3L6rhTu4vjivPrqp/ts9P9qgtEHXw7p/AXviAo6GuwVQv0BstuqpbDuzN5c5rVo3wGCVP8yIYJR211w7grnwZPvic3Jb7WiwYzkXX3cfsVZubb3LUQgt1GZsAgilXM5nrkWfn7Q9ZmUTgxP0XkgbfiWlEr4OG54kQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741241571; c=relaxed/simple; bh=4iDBRxTwji7W2TQy4yPD5QDaGlyxwd8lWIRxM9oQpQA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=osY5NEKDDEHtYwRxFWNv7AgODqa6mTCvqGgdEzN3VCu1mvlCO4jkZScu7e8UVHSW4gbLu19UomAoJMC1Ah8NTrKGnooYuQhZ7qevyWNHK2qjqUOrvt5EJ9pJGtM4Wd1FiY9hcHbnCt+eDQyAz6EENUFgzgos8dSV7EXTueJMuCo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=nebOxELY; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="nebOxELY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E8AEFC4CEE4; Thu, 6 Mar 2025 06:12:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1741241571; bh=4iDBRxTwji7W2TQy4yPD5QDaGlyxwd8lWIRxM9oQpQA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=nebOxELYtScjRAAYyHTl3X/sJuEPF7zfO2N7x2Dd/YHYOSh9rLuy0PrXBW1ZJY++y 249KaGGqJPRm1wE4mUHwVGrZK1jDlfFSUKHe54JcX2lR5lMd3QFwUCJjBnwLxxFdCR 3r5wCG4r4dcXD3fXJb72WoSDKeDND3LkS/EhKcyvMSouv5iYn81VmSdvpLPgonKw1T YPnqfQBbY4kk5wsC69DQyg1w8XbDSyu2FppTuGvoNOhCXgoqwrjINnhOFv9ZL1C/NE Ka2dOWuANApqbiRpi9LgSOOMvJe1oUri3M9JaEAdqNbh9Pkoz7QTu+qf5HnbfaHdhW bNJHOstZKNS4A== Date: Wed, 5 Mar 2025 22:12:47 -0800 From: Kees Cook To: Nathan Chancellor Cc: Thomas =?iso-8859-1?Q?Wei=DFschuh?= , Nick Desaulniers , Bill Wendling , Justin Stitt , Masahiro Yamada , Nicolas Schier , llvm@lists.linux.dev, linux-kbuild@vger.kernel.org, David Gow , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH] kbuild: clang: Support building UM with SUBARCH=i386 Message-ID: <202503052208.8CC5A355A7@keescook> References: <20250303215240.work.379-kees@kernel.org> <05a25510-ab44-4eb1-a878-71e84c8aff0d@t-8ch.de> <20250304102536.GB2529736@ax162> <202503040842.1177A1F15B@keescook> <20250305144554.GA3574115@ax162> Precedence: bulk X-Mailing-List: linux-kbuild@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250305144554.GA3574115@ax162> On Wed, Mar 05, 2025 at 03:45:54PM +0100, Nathan Chancellor wrote: > On Tue, Mar 04, 2025 at 09:07:57AM -0800, Kees Cook wrote: > > On Tue, Mar 04, 2025 at 03:51:19PM +0100, Thomas Weißschuh wrote: > > > No, it doesn't. > > > > > > Running tests with: > > > $ .kunit/linux kunit.filter_glob=overflow.DEFINE_FLEX_test kunit.enable=1 mem=1G console=tty kunit_shutdown=halt > > > [15:48:30] =================== overflow (1 subtest) =================== > > > [15:48:30] # DEFINE_FLEX_test: EXPECTATION FAILED at lib/overflow_kunit.c:1200 > > > [15:48:30] Expected __builtin_dynamic_object_size(two_but_zero, 0) == expected_raw_size, but > > > [15:48:30] __builtin_dynamic_object_size(two_but_zero, 0) == 12 (0xc) > > > [15:48:30] expected_raw_size == 8 (0x8) > > > [15:48:30] [FAILED] DEFINE_FLEX_test > > > [15:48:30] # module: overflow_kunit > > > [15:48:30] ==================== [FAILED] overflow ===================== > > > [15:48:30] ============================================================ > > > [15:48:30] Testing complete. Ran 1 tests: failed: 1 > > > [15:48:31] Elapsed time: 43.985s total, 0.001s configuring, 43.818s building, 0.133s running > > > > > > If I force CONFIG_CC_HAS_COUNTED_BY=n then the test succeeds. > > > Clang 19.1.7 from the Arch Linux repos. > > > > I wasn't seeing with Clang 20 from git: > > ClangBuiltLinux clang version 20.0.0git (git@github.com:llvm/llvm-project.git 72901fe19eb1e55d0ee1c380ab7a9f57d2f187c5) > > > > But I do see the error with ToT Clang: > > ClangBuiltLinux clang version 21.0.0git (git@github.com:llvm/llvm-project.git eee3db5421040cfc3eae6e92ed714650a6f741fa) > > > > Clang 17.1: (does not support counted_by) > > > > # DEFINE_FLEX_test: missing counted_by > > # DEFINE_FLEX_test: sizeof(two_but_zero): 8 > > # DEFINE_FLEX_test: __struct_size(two_but_zero): 12 > > # DEFINE_FLEX_test: __member_size(two_but_zero): 12 > > # DEFINE_FLEX_test: __member_size(two_but_zero->array): 4 > > > > Clang 19.1.1: (actually is _does_ support counted_by, but Linux disables it) > > > > # DEFINE_FLEX_test: missing counted_by > > # DEFINE_FLEX_test: sizeof(two_but_zero): 8 > > # DEFINE_FLEX_test: __struct_size(two_but_zero): 12 > > # DEFINE_FLEX_test: __member_size(two_but_zero): 12 > > # DEFINE_FLEX_test: __member_size(two_but_zero->array): 4 > > > > GCC 13.3: > > > > # DEFINE_FLEX_test: missing counted_by > > # DEFINE_FLEX_test: sizeof(two_but_zero): 8 > > # DEFINE_FLEX_test: __struct_size(two_but_zero): 12 > > # DEFINE_FLEX_test: __member_size(two_but_zero): 12 > > # DEFINE_FLEX_test: __member_size(two_but_zero->array): 4 > > > > Clang 21 (ToT): > > > > # DEFINE_FLEX_test: has counted_by > > # DEFINE_FLEX_test: sizeof(two_but_zero): 8 > > # DEFINE_FLEX_test: __struct_size(two_but_zero): 12 > > # DEFINE_FLEX_test: __member_size(two_but_zero): 12 > > # DEFINE_FLEX_test: __member_size(two_but_zero->array): 0 > > > > GCC 15 (ToT): > > > > # DEFINE_FLEX_test: has counted_by > > # DEFINE_FLEX_test: sizeof(two_but_zero): 8 > > # DEFINE_FLEX_test: __struct_size(two_but_zero): 12 > > # DEFINE_FLEX_test: __member_size(two_but_zero): 12 > > # DEFINE_FLEX_test: __member_size(two_but_zero->array): 0 > > > > It seems like the on-stack sizes with __bdos all agree now, regardless > > of the used compiler features. It is only the array size calculation > > that now gets masked by counted_by. (i.e. the stack size is overridden > > by the zero "count" for the array elements.) > > > > I'll send a fix for the test... > > Just for my own understanding, is this because of the adjustment that > Bill did to the __bdos() calculation in [1]? I think that tracks because > the version of LLVM 20 that you have is pretty old and does not have > that change. I know for a fact I tested the original change to the > overflow KUnit test to adjust the expected calculation result and it > passed but it was before that change as well. If I use a current version > of LLVM 20, I see the failure. If I allow LLVM 18 to use __counted_by(), > the test passes with it. Not that it truly matters but it does explain > how we got to this point. Yes, totally! This is exactly how I got there too. Great; thank you for summarizing! :) -- Kees Cook