From patchwork Wed Jan 8 10:23:03 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ard Biesheuvel X-Patchwork-Id: 206645 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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 D62C9C33C9E for ; Wed, 8 Jan 2020 10:23:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ADFC12075D for ; Wed, 8 Jan 2020 10:23:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578478997; bh=850Gzv2RRXpgVvFLdzqsajavn+oWE12MwONFtdvvECw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=gfiaWjrRXpi2s41XZR2A1Im90tpsAXvhCeaXWOFk1znPfwdlyXftYFB0HO+oAJtIt IimGXsXOOLFJMz0h7OpvSI8lXcC1QUHr/UI4mfbPrXmeL8MD3bDlKBwSLzCvEYv+eN HmvflWDx/9bmXqgz5vYmdN076IDEdkcnTG9tM6rs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727129AbgAHKXO (ORCPT ); Wed, 8 Jan 2020 05:23:14 -0500 Received: from mail.kernel.org ([198.145.29.99]:49754 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726144AbgAHKXO (ORCPT ); Wed, 8 Jan 2020 05:23:14 -0500 Received: from localhost.localdomain (amontpellier-657-1-18-247.w109-210.abo.wanadoo.fr [109.210.65.247]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EF31920848; Wed, 8 Jan 2020 10:23:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578478993; bh=850Gzv2RRXpgVvFLdzqsajavn+oWE12MwONFtdvvECw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=dJEGpOQLTCzYG3nGEE7oplTGup89llsZJf0KbfrRxSy77gQYKbM77EGogPfxd1zgs mOngeFn/rJHEl5A4n6iy7mKH7u9DETeHTrtd9A75J1AgaR5xu8LsfXosTsX0VL1e+V baHkUx5WR1qZW7t1SYOklHglPSXg2HSqpBsIhbkI= From: Ard Biesheuvel To: linux-efi@vger.kernel.org Cc: x86@kernel.org, luto@kernel.org, linux-kernel@vger.kernel.org, Ard Biesheuvel , Maarten Lankhorst , Linus Torvalds , Arvind Sankar Subject: [RFC PATCH 2/3] x86/boot/compressed: force hidden visibility for all symbol references Date: Wed, 8 Jan 2020 11:23:03 +0100 Message-Id: <20200108102304.25800-3-ardb@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200108102304.25800-1-ardb@kernel.org> References: <20200108102304.25800-1-ardb@kernel.org> MIME-Version: 1.0 Sender: linux-efi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-efi@vger.kernel.org Eliminate all GOT entries in the decompressor binary, by forcing hidden visibility for all symbol references, which informs the compiler that such references will be resolved at link time without the need for allocating GOT entries. To ensure that no GOT entries will creep back in, add an assertion to the decompressor linker script that will fire if the .got section has a non-zero size. Signed-off-by: Ard Biesheuvel --- arch/x86/boot/compressed/Makefile | 1 + arch/x86/boot/compressed/hidden.h | 19 +++++++++++++++++++ arch/x86/boot/compressed/vmlinux.lds.S | 1 + 3 files changed, 21 insertions(+) diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 56aa5fa0a66b..361df91b2288 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -39,6 +39,7 @@ KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) KBUILD_CFLAGS += $(call cc-disable-warning, gnu) KBUILD_CFLAGS += -Wno-pointer-sign KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) +KBUILD_CFLAGS += -include hidden.h KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__ GCOV_PROFILE := n diff --git a/arch/x86/boot/compressed/hidden.h b/arch/x86/boot/compressed/hidden.h new file mode 100644 index 000000000000..2a1693373cc7 --- /dev/null +++ b/arch/x86/boot/compressed/hidden.h @@ -0,0 +1,19 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * When building position independent code with GCC using the -fPIC option, + * (or even the -fPIE one on older versions), it will assume that we are + * building a dynamic object (either a shared library or an executable) that + * may have symbol references that can only be resolved at load time. For a + * variety of reasons (ELF symbol preemption, the CoW footprint of the section + * that is modified by the loader), this results in all references to symbols + * with external linkage to go via entries in the Global Offset Table (GOT), + * which carries absolute addresses which need to be fixed up when the + * executable image is loaded at an offset which is different from its link + * time offset. + * + * Fortunately, there is a way to inform the compiler that such symbol + * references will be satisfied at link time rather than at load time, by + * giving them 'hidden' visibility. + */ + +#pragma GCC visibility push(hidden) diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S index 51ca654e43a9..955496ff2fcd 100644 --- a/arch/x86/boot/compressed/vmlinux.lds.S +++ b/arch/x86/boot/compressed/vmlinux.lds.S @@ -78,6 +78,7 @@ SECTIONS _end = .; } +ASSERT (SIZEOF(.got) == 0, "Unexpected GOT entries detected!") #ifdef CONFIG_X86_64 ASSERT (SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18, "Unexpected GOT/PLT entries detected!")