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=-13.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 31DC0C433E5 for ; Wed, 15 Jul 2020 00:41:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 14A9B20674 for ; Wed, 15 Jul 2020 00:41:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728061AbgGOAll (ORCPT ); Tue, 14 Jul 2020 20:41:41 -0400 Received: from mail-qv1-f67.google.com ([209.85.219.67]:42460 "EHLO mail-qv1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726970AbgGOAlj (ORCPT ); Tue, 14 Jul 2020 20:41:39 -0400 Received: by mail-qv1-f67.google.com with SMTP id dm12so156197qvb.9 for ; Tue, 14 Jul 2020 17:41:37 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=OKhnBxItrBTpXf+LwQ8W3IeeewHkHEBu9msI4n5LC4M=; b=Zz3QQbJRgiGJ6j+obTjJ8olBiUXAN+NGsgPwwQKukALPTTo/BYW8GCR2iNvqQMGoVY WIqCOcu5kHM4IVUcFfn1zEIhHcp2OMRmyxVRLggeZ5UF1lu33Ohk1rLi3TaM869wmNgr /oQYiwtNrTjkuRO88EB2VzFuVNSUD3KFbzyvngiFKuqEIiWz1m9kEjY/7uCYwNZao1xh ncfLnkYXMpxOnGARp7vD6rAMAiXBUyKu+zyZ401H6eC8NTl+huXDWe536vdjlDs2dqQ/ RaCRq/fPTFvDi4gKSpmM/89haJqc+wI9TzTmMYUE8GKmfUKVihPK35Y9Ad1HJ1x/Pzzk hJow== X-Gm-Message-State: AOAM532jrqOu3DWk3ApQJRdAkUlgwGDs0bYh2JGMBDFFQKCex8FTuHED 69zTvBeyGYSQBScZuBeVVio= X-Google-Smtp-Source: ABdhPJwWq9YOiLuMEeKGHmT/TRM56fws6/niuwAGiKS44dizqiYZ6K74iLcFidopjNSgnzmiVk7Unw== X-Received: by 2002:a0c:aa15:: with SMTP id d21mr6857915qvb.155.1594773697224; Tue, 14 Jul 2020 17:41:37 -0700 (PDT) Received: from rani.riverdale.lan ([2001:470:1f07:5f3::b55f]) by smtp.gmail.com with ESMTPSA id c9sm524776qko.24.2020.07.14.17.41.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Jul 2020 17:41:36 -0700 (PDT) From: Arvind Sankar To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , x86@kernel.org Cc: Nick Desaulniers , Fangrui Song , Dmitry Golovin , clang-built-linux@googlegroups.com, Ard Biesheuvel , Masahiro Yamada , Daniel Kiper , Sedat Dilek , Kees Cook , Nathan Chancellor , Arnd Bergmann , "H . J . Lu" , linux-kernel@vger.kernel.org Subject: [PATCH v5 2/7] x86/boot/compressed: Force hidden visibility for all symbol references Date: Tue, 14 Jul 2020 20:41:28 -0400 Message-Id: <20200715004133.1430068-3-nivedita@alum.mit.edu> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200714023836.2310569-1-nivedita@alum.mit.edu> References: <20200714023836.2310569-1-nivedita@alum.mit.edu> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Ard Biesheuvel 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. [Arvind: move hidden.h to include/linux instead of making a copy] Reviewed-by: Kees Cook Signed-off-by: Ard Biesheuvel Acked-by: Arvind Sankar Signed-off-by: Arvind Sankar From: Ard Biesheuvel Link: https://lore.kernel.org/r/20200523120021.34996-3-ardb@kernel.org --- arch/x86/boot/compressed/Makefile | 1 + arch/x86/boot/compressed/vmlinux.lds.S | 1 + drivers/firmware/efi/libstub/Makefile | 2 +- drivers/firmware/efi/libstub/hidden.h | 6 ------ include/linux/hidden.h | 19 +++++++++++++++++++ 5 files changed, 22 insertions(+), 7 deletions(-) delete mode 100644 drivers/firmware/efi/libstub/hidden.h create mode 100644 include/linux/hidden.h diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 7619742f91c9..c829d874dcac 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -42,6 +42,7 @@ KBUILD_CFLAGS += $(call cc-disable-warning, gnu) KBUILD_CFLAGS += -Wno-pointer-sign KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) KBUILD_CFLAGS += -fno-asynchronous-unwind-tables +KBUILD_CFLAGS += -include $(srctree)/include/linux/hidden.h KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__ GCOV_PROFILE := n diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S index b17d218ccdf9..4bcc943842ab 100644 --- a/arch/x86/boot/compressed/vmlinux.lds.S +++ b/arch/x86/boot/compressed/vmlinux.lds.S @@ -81,6 +81,7 @@ SECTIONS DISCARDS } +ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!") #ifdef CONFIG_X86_64 ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18, "Unexpected GOT/PLT entries detected!") #else diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile index 4cce372edaf4..609157a40493 100644 --- a/drivers/firmware/efi/libstub/Makefile +++ b/drivers/firmware/efi/libstub/Makefile @@ -27,7 +27,7 @@ cflags-$(CONFIG_ARM) := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \ cflags-$(CONFIG_EFI_GENERIC_STUB) += -I$(srctree)/scripts/dtc/libfdt KBUILD_CFLAGS := $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \ - -include $(srctree)/drivers/firmware/efi/libstub/hidden.h \ + -include $(srctree)/include/linux/hidden.h \ -D__NO_FORTIFY \ $(call cc-option,-ffreestanding) \ $(call cc-option,-fno-stack-protector) \ diff --git a/drivers/firmware/efi/libstub/hidden.h b/drivers/firmware/efi/libstub/hidden.h deleted file mode 100644 index 3493b041f419..000000000000 --- a/drivers/firmware/efi/libstub/hidden.h +++ /dev/null @@ -1,6 +0,0 @@ -/* SPDX-License-Identifier: GPL-2.0 */ -/* - * To prevent the compiler from emitting GOT-indirected (and thus absolute) - * references to any global symbols, override their visibility as 'hidden' - */ -#pragma GCC visibility push(hidden) diff --git a/include/linux/hidden.h b/include/linux/hidden.h new file mode 100644 index 000000000000..49a17b6b5962 --- /dev/null +++ b/include/linux/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) -- 2.26.2