From patchwork Sun Nov 14 00:57:25 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Gustavo A. R. Silva" X-Patchwork-Id: 12617743 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A54C3C433F5 for ; Sun, 14 Nov 2021 00:52:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6DD3560E97 for ; Sun, 14 Nov 2021 00:52:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231736AbhKNAzS (ORCPT ); Sat, 13 Nov 2021 19:55:18 -0500 Received: from mail.kernel.org ([198.145.29.99]:36494 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229988AbhKNAzS (ORCPT ); Sat, 13 Nov 2021 19:55:18 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 9ED0B60E08; Sun, 14 Nov 2021 00:52:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1636851145; bh=a7rUixXoOZQp5X2wsqpJXaQKajCRpv8Zr8OGdkADNKE=; h=Date:From:To:Cc:Subject:From; b=I6z0nfnmBkhxShhcNHI2xLBcXgJlYR/PpE7wePerxMdrN1itMua/M48YN3hcr+KzT PtkU62WHBnsA0KyBRDcgZqzkIzUYeyJxx28aTseUvZoyIxhfFaRUy2rpILoGLRgJea ugnkXbF4GLa4BmJu0jCvhTquUecxgYkjcXtBmKUagLQn8G3wD++5HgagKeSYvPOmf0 pg50BJ71JYA6Hk4tJ78r9kl6lilk9Ud33MsIMV1oIPBB/7/sxD+r1bG1Twg6QLckBb Ela3NnrNA4uFxTxvBhMGNPJbtXzazGcCRxBwz8WJeK6TQ/i2E6vxpFZmKCUVR/Iy0Z c+7SigdMfTw6w== Date: Sat, 13 Nov 2021 18:57:25 -0600 From: "Gustavo A. R. Silva" To: Linus Torvalds Cc: Kees Cook , linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" , linux-hardening@vger.kernel.org Subject: [PATCH] kconfig: Add support for -Wimplicit-fallthrough Message-ID: <20211114005725.GA27075@embeddedor> MIME-Version: 1.0 Content-Disposition: inline Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org Add Kconfig support for -Wimplicit-fallthrough for both GCC and Clang. The compiler option is under configuration CC_IMPLICIT_FALLTHROUGH, which is enabled by default. Special thanks to Nathan Chancellor who fixed the Clang bug[1][2]. This bugfix only appears in Clang 14.0.0, so older versions still contain the bug and -Wimplicit-fallthrough won't be enabled for them, for now. This concludes a long journey and now we are finally getting rid of the unintentional fallthrough bug-class in the kernel, entirely. :) [1] https://github.com/llvm/llvm-project/commit/9ed4a94d6451046a51ef393cd62f00710820a7e8 [2] https://bugs.llvm.org/show_bug.cgi?id=51094 Link: https://github.com/KSPP/linux/issues/115 Link: https://github.com/ClangBuiltLinux/linux/issues/236 Co-developed-by: Kees Cook Signed-off-by: Kees Cook Co-developed-by: Linus Torvalds Signed-off-by: Linus Torvalds Signed-off-by: Gustavo A. R. Silva Reviewed-by: Nathan Chancellor Tested-by: Nathan Chancellor --- Makefile | 6 +----- init/Kconfig | 5 +++++ 2 files changed, 6 insertions(+), 5 deletions(-) diff --git a/Makefile b/Makefile index 30c7c81d0437..f18a50daad00 100644 --- a/Makefile +++ b/Makefile @@ -786,7 +786,7 @@ stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG) := -fstack-protector-strong KBUILD_CFLAGS += $(stackp-flags-y) KBUILD_CFLAGS-$(CONFIG_WERROR) += -Werror -KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) +KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH) ifdef CONFIG_CC_IS_CLANG KBUILD_CPPFLAGS += -Qunused-arguments @@ -798,10 +798,6 @@ KBUILD_CFLAGS += -Wno-gnu KBUILD_CFLAGS += -mno-global-merge else -# Warn about unmarked fall-throughs in switch statement. -# Disabled for clang while comment to attribute conversion happens and -# https://github.com/ClangBuiltLinux/linux/issues/636 is discussed. -KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough=5,) # gcc inanely warns about local variables called 'main' KBUILD_CFLAGS += -Wno-main endif diff --git a/init/Kconfig b/init/Kconfig index 11f8a845f259..b0582cd3e096 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -885,6 +885,11 @@ config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH config CC_HAS_INT128 def_bool !$(cc-option,$(m64-flag) -D__SIZEOF_INT128__=0) && 64BIT +config CC_IMPLICIT_FALLTHROUGH + string + default "-Wimplicit-fallthrough=5" if CC_IS_GCC + default "-Wimplicit-fallthrough" if CC_IS_CLANG && $(cc-option,-Wunreachable-code-fallthrough) + # # For architectures that know their GCC __int128 support is sound #