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 442392153EA; Wed, 8 Apr 2026 22:03:39 +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=1775685819; cv=none; b=mTZMKtppChVZwWALpTV+okwdb+aDmCQuXDSzqhx+q4X5JGWTjxJ4lfmZ4WZ2WXBZSOQwINVbCn/vvtJeCxTAtOY2ANjnB0bF/FEa70D+jzszYhW3iZW6jPqtsmqT38g1/aW/gl1mxbO5ewUNLSqWoq891DjTuP6VMNZ4OcKk5gU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775685819; c=relaxed/simple; bh=Yjer5woEh3mw3RtpKNVTvZ9uyG6f8sJECUD6FN73R+Y=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=NIOWb1I8ZdvOmigIaVOpPQGZ+UQBYk8gwuEHoNxCCsLcDIgMZcIP6t1scZ0cWZXHW++9QOiUB4qQCcjRvVAUW6pjZ7HoA5l/qOtW+dbTsH9GnpCgfLzVXi6sSZKAJPPLpdnipPTMUbT8HhXcQjHjMw4NHukes9lqFuAyzen5rgA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pp5wLYIt; 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="pp5wLYIt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 005AEC19421; Wed, 8 Apr 2026 22:03:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775685818; bh=Yjer5woEh3mw3RtpKNVTvZ9uyG6f8sJECUD6FN73R+Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=pp5wLYIt1R7KEOiJQQnXW6ZhJEmjf9UvC06DcsgIrDzefnDIeilwMVXldNCwWtFt4 uNVmQ0+glAJB5Db5wzHoDlmnmC3M8IdK9/qXJEtnwQsntoI2MBPp1TfmeM/BUo95fR KDqeF6riY5+LsrJ1r+DJeNZ890kQRurbE1c7I163hs/oNGExGQVy5mb7Kxqt9HSb90 3rz3Q+F3lmb2gxwpP1FDt+wioHBLLtRdyhANIn2ZUARYPWvglVD2owgocjtsmbIleD hVHwwiktZDlsAmEMCfdnc9IBDHHOaujHTpShcIdyn7QDDdLTLmQd8eUfkSqIyO+MA/ yhlcfB71P7Oyg== Date: Wed, 8 Apr 2026 15:03:34 -0700 From: Nathan Chancellor To: Kees Cook Cc: Peter Oberparleiter , kernel test robot , Nick Desaulniers , Bill Wendling , Justin Stitt , llvm@lists.linux.dev, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH v2] gcov: Disable GCOV_PROFILE_ALL on 32-bit UML with Clang 20/21 Message-ID: <20260408220334.GA3962465@ax162> References: <20260408162607.it.347-kees@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260408162607.it.347-kees@kernel.org> On Wed, Apr 08, 2026 at 09:26:12AM -0700, Kees Cook wrote: > Clang 20 and 21 miscompute __builtin_object_size() when -fprofile-arcs > is active on 32-bit UML targets, which passes incorrect object size > calculations for local variables through always_inline copy_to_user() > and check_copy_size(), causing spurious compile-time errors: > > include/linux/ucopysize.h:52:4: error: call to '__bad_copy_from' declared with 'error' attribute: copy source size is too small > > The regression was introduced in LLVM commit 02b8ee281947 ("[llvm] > Improve llvm.objectsize computation by computing GEP, alloca and malloc > parameters bound"), which shipped in Clang 20. It was fixed in LLVM > by commit 45b697e610fd ("[MemoryBuiltins] Consider index type size > when aggregating gep offsets"), which was backported to the LLVM 22.x > release branch. > > The bug requires 32-bit UML + GCOV_PROFILE_ALL (which uses -fprofile-arcs), > though the exact trigger depends on optimizer decisions influenced by other > enabled configs. > > Prevent the broken combination by disabling GCOV_PROFILE_ALL on 32-bit > UML when using Clang 20.x or 21.x. > > Reported-by: kernel test robot > Closes: https://lore.kernel.org/oe-kbuild-all/202604030531.O6FveVgn-lkp@intel.com/ > Assisted-by: Claude:claude-opus-4-6[1m] > Signed-off-by: Kees Cook > --- > v2: fixed typo in version comparison: needed < not <= (Sashiko) > v1: https://lore.kernel.org/lkml/20260408005958.work.271-kees@kernel.org/ > Cc: Peter Oberparleiter > Cc: Nathan Chancellor > Cc: Nick Desaulniers > Cc: Bill Wendling > Cc: Justin Stitt > Cc: > --- > kernel/gcov/Kconfig | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/kernel/gcov/Kconfig b/kernel/gcov/Kconfig > index 04f4ebdc3cf5..56abff785654 100644 > --- a/kernel/gcov/Kconfig > +++ b/kernel/gcov/Kconfi > @@ -42,6 +42,9 @@ config GCOV_PROFILE_ALL > depends on !COMPILE_TEST > depends on GCOV_KERNEL > depends on ARCH_HAS_GCOV_PROFILE_ALL Would it be better to avoid selecting this symbol in arch/um/Kconfig when we have this condition? > + # Clang 20 & 21 miscompute __builtin_object_size() under -fprofile-arcs > + # on 32-bit UML, causing spurious compile-time errors in check_copy_size(). > + depends on !(UML && !64BIT && CC_IS_CLANG && CLANG_VERSION >= 200000 && CLANG_VERSION < 220100) Given that you have an inclusive range above 0, you could drop the CC_IS_CLANG. With the suggestion above it would just become: diff --git a/arch/um/Kconfig b/arch/um/Kconfig index 098cda44db22..d9541d13d9eb 100644 --- a/arch/um/Kconfig +++ b/arch/um/Kconfig @@ -11,7 +11,9 @@ config UML select ARCH_HAS_CACHE_LINE_SIZE select ARCH_HAS_CPU_FINALIZE_INIT select ARCH_HAS_FORTIFY_SOURCE - select ARCH_HAS_GCOV_PROFILE_ALL + # Clang 20 & 21 miscompute __builtin_object_size() under -fprofile-arcs + # on 32-bit, causing spurious compile-time errors in check_copy_size(). + select ARCH_HAS_GCOV_PROFILE_ALL if !(!64BIT && CLANG_VERSION >= 200000 && CLANG_VERSION < 220100) select ARCH_HAS_KCOV select ARCH_HAS_STRNCPY_FROM_USER select ARCH_HAS_STRNLEN_USER -- Cheers, Nathan