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=-16.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham 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 81611C43465 for ; Mon, 21 Sep 2020 16:50:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2EE5E23888 for ; Mon, 21 Sep 2020 16:50:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600707018; bh=rNiWjmW70ZzjJzIF8efbR/VjEyRCpozTf42Ez/2euoo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=1evQuFGx4p12Bazl/JNC2qfbKhcp4+o6AW55Kk/iIy1Pi/8oz9AFBb1jRRkOzhNM4 JzOQhevjygPi9hsh7/SCqf7TZyv4zX//5zYEs5vCvMpLKSrJttNquSYqIK+5UK/Y7K VYRZtmvrE5mKemT4b11kiuY8qnr7ROrVdtqQ8T6g= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728436AbgIUQuR (ORCPT ); Mon, 21 Sep 2020 12:50:17 -0400 Received: from mail.kernel.org ([198.145.29.99]:58602 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729988AbgIUQuO (ORCPT ); Mon, 21 Sep 2020 12:50:14 -0400 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4D170238A1; Mon, 21 Sep 2020 16:50:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600707013; bh=rNiWjmW70ZzjJzIF8efbR/VjEyRCpozTf42Ez/2euoo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pZ3AQT2jNUq/3eGjdnKoeAc2y9lbM7PKbX2087Q5dXzARdXqKmdXp6lO/woLYXLb8 YjQaW4vzJVGsnqtb+hxPJC6ZWhEdmkxfFWQEnky0NEQ+zFeSlAWMKVN96lAfiibD3l /YL9WLT2NWcFs/qKBLKgDFqYWFBlrBlRQ+x7iR54= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Nick Desaulniers , Arvind Sankar , Ingo Molnar , Sedat Dilek , Ard Biesheuvel Subject: [PATCH 5.4 64/72] x86/boot/compressed: Disable relocation relaxation Date: Mon, 21 Sep 2020 18:31:43 +0200 Message-Id: <20200921163124.913173056@linuxfoundation.org> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20200921163121.870386357@linuxfoundation.org> References: <20200921163121.870386357@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Arvind Sankar commit 09e43968db40c33a73e9ddbfd937f46d5c334924 upstream. The x86-64 psABI [0] specifies special relocation types (R_X86_64_[REX_]GOTPCRELX) for indirection through the Global Offset Table, semantically equivalent to R_X86_64_GOTPCREL, which the linker can take advantage of for optimization (relaxation) at link time. This is supported by LLD and binutils versions 2.26 onwards. The compressed kernel is position-independent code, however, when using LLD or binutils versions before 2.27, it must be linked without the -pie option. In this case, the linker may optimize certain instructions into a non-position-independent form, by converting foo@GOTPCREL(%rip) to $foo. This potential issue has been present with LLD and binutils-2.26 for a long time, but it has never manifested itself before now: - LLD and binutils-2.26 only relax movq foo@GOTPCREL(%rip), %reg to leaq foo(%rip), %reg which is still position-independent, rather than mov $foo, %reg which is permitted by the psABI when -pie is not enabled. - GCC happens to only generate GOTPCREL relocations on mov instructions. - CLang does generate GOTPCREL relocations on non-mov instructions, but when building the compressed kernel, it uses its integrated assembler (due to the redefinition of KBUILD_CFLAGS dropping -no-integrated-as), which has so far defaulted to not generating the GOTPCRELX relocations. Nick Desaulniers reports [1,2]: "A recent change [3] to a default value of configuration variable (ENABLE_X86_RELAX_RELOCATIONS OFF -> ON) in LLVM now causes Clang's integrated assembler to emit R_X86_64_GOTPCRELX/R_X86_64_REX_GOTPCRELX relocations. LLD will relax instructions with these relocations based on whether the image is being linked as position independent or not. When not, then LLD will relax these instructions to use absolute addressing mode (R_RELAX_GOT_PC_NOPIC). This causes kernels built with Clang and linked with LLD to fail to boot." Patch series [4] is a solution to allow the compressed kernel to be linked with -pie unconditionally, but even if merged is unlikely to be backported. As a simple solution that can be applied to stable as well, prevent the assembler from generating the relaxed relocation types using the -mrelax-relocations=no option. For ease of backporting, do this unconditionally. [0] https://gitlab.com/x86-psABIs/x86-64-ABI/-/blob/master/x86-64-ABI/linker-optimization.tex#L65 [1] https://lore.kernel.org/lkml/20200807194100.3570838-1-ndesaulniers@google.com/ [2] https://github.com/ClangBuiltLinux/linux/issues/1121 [3] https://reviews.llvm.org/rGc41a18cf61790fc898dcda1055c3efbf442c14c0 [4] https://lore.kernel.org/lkml/20200731202738.2577854-1-nivedita@alum.mit.edu/ Reported-by: Nick Desaulniers Signed-off-by: Arvind Sankar Signed-off-by: Ingo Molnar Tested-by: Nick Desaulniers Tested-by: Sedat Dilek Acked-by: Ard Biesheuvel Reviewed-by: Nick Desaulniers Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20200812004308.1448603-1-nivedita@alum.mit.edu Signed-off-by: Greg Kroah-Hartman --- arch/x86/boot/compressed/Makefile | 2 ++ 1 file changed, 2 insertions(+) --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -38,6 +38,8 @@ KBUILD_CFLAGS += $(call cc-option,-fno-s KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) KBUILD_CFLAGS += $(call cc-disable-warning, gnu) KBUILD_CFLAGS += -Wno-pointer-sign +# Disable relocation relaxation in case the link is not PIE. +KBUILD_CFLAGS += $(call as-option,-Wa$(comma)-mrelax-relocations=no) KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__ GCOV_PROFILE := n