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=-17.8 required=3.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED,DKIM_INVALID,DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,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 94F92C43461 for ; Thu, 3 Sep 2020 20:40:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6B7D820897 for ; Thu, 3 Sep 2020 20:40:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=google.com header.i=@google.com header.b="BAqToBhe" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729774AbgICUkf (ORCPT ); Thu, 3 Sep 2020 16:40:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35450 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729356AbgICUbD (ORCPT ); Thu, 3 Sep 2020 16:31:03 -0400 Received: from mail-qv1-xf49.google.com (mail-qv1-xf49.google.com [IPv6:2607:f8b0:4864:20::f49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7314CC061261 for ; Thu, 3 Sep 2020 13:30:57 -0700 (PDT) Received: by mail-qv1-xf49.google.com with SMTP id q4so2502969qvr.10 for ; Thu, 03 Sep 2020 13:30:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:in-reply-to:message-id:mime-version:references:subject :from:to:cc; bh=mDVvkNnwHRt+Li8nefuHvmgwU3VCsthhxmclA+Biet0=; b=BAqToBhePk+irZIVVLAwecMp1XW9+Ks/f/sHbDKoGAGhsn6UE+3DQRUDeqOb8say/o QxpBeEZ6aAX0zEfibyHBFmhzl0Vw+o0mHntVCknw3JFLb1KRs5PinJ6tHxAOk5MN5EYA AfgwLGhevAbhgMH2td9x/PyO+G3DTP7s1GxaKtrd39cb0JzoBHskqiAq/LJEw/gMn8iA XT4V4BL0iYhatzNnu1bXuTQZJGInDJpEfjNk2sRcKcORI1v3DBYhfh8RDI2LHTVrDtsI V29No/TKC195kYLq9pmO7w16CLGuBlaDY8z5c/lcwnflHFClTnlapgui3DYxttVqDUEE tSLQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=mDVvkNnwHRt+Li8nefuHvmgwU3VCsthhxmclA+Biet0=; b=Z9a6d9SmohNL6/hAVnEwFwhLAPksGdDmtus2SMgDSvQ+YJVQVXSKQlJuylW3LV4SQ2 swxIos5lKLRHmlEvOkeLrItQ6rl1/4xJBB8UVszP8qDy4QOh1FU2wE1+3kimKDkRdZUs uEu+7rU+RS34GcjZPDJ+29498tMLo0zkrVkNh0PTrFWSVLbbsVUIr/fTpV7MuuvQpUUX u3531onBVZLV1hze3A6MjatUuwZTtdn0hV2wFAg5/tWNZRMZIxPeBkDGN6gj6ykev3NH ikMbOZqu0yRWQUyg8zIjUiHafZ13M3qj0rRUONsh/y4swukeMRYcRXw4fUEa11yioJJU HwTw== X-Gm-Message-State: AOAM533B7l1wP2iNvoL1XOWYLFUb8ZN3Nl/ZY1pNI5/UAVf0sFJwni5o 6GUuPEgpgelWTNX3Ff/78/DK5nW3mu7pQ1BmCQ8= X-Google-Smtp-Source: ABdhPJyUnW2qSfmEzLjPskwcMhWUurVS5skiaBz/vWVhXl7N7pyUdqZoSu6Ssyc74PFkWqrXo2ggCEF9Y0h+Jfi/JHo= X-Received: from samitolvanen1.mtv.corp.google.com ([2620:15c:201:2:f693:9fff:fef4:1b6d]) (user=samitolvanen job=sendgmr) by 2002:a05:6214:292:: with SMTP id l18mr3616010qvv.3.1599165056576; Thu, 03 Sep 2020 13:30:56 -0700 (PDT) Date: Thu, 3 Sep 2020 13:30:26 -0700 In-Reply-To: <20200903203053.3411268-1-samitolvanen@google.com> Message-Id: <20200903203053.3411268-2-samitolvanen@google.com> Mime-Version: 1.0 References: <20200624203200.78870-1-samitolvanen@google.com> <20200903203053.3411268-1-samitolvanen@google.com> X-Mailer: git-send-email 2.28.0.526.ge36021eeef-goog Subject: [PATCH v2 01/28] x86/boot/compressed: Disable relocation relaxation From: Sami Tolvanen To: Masahiro Yamada , Will Deacon Cc: Peter Zijlstra , Steven Rostedt , Greg Kroah-Hartman , "Paul E. McKenney" , Kees Cook , Nick Desaulniers , clang-built-linux@googlegroups.com, kernel-hardening@lists.openwall.com, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, x86@kernel.org, Arvind Sankar Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Arvind Sankar 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 Tested-by: Nick Desaulniers Tested-by: Sedat Dilek Reviewed-by: Nick Desaulniers Cc: stable@vger.kernel.org --- arch/x86/boot/compressed/Makefile | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 3962f592633d..ff7894f39e0e 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -43,6 +43,8 @@ KBUILD_CFLAGS += -Wno-pointer-sign KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) KBUILD_CFLAGS += -fno-asynchronous-unwind-tables KBUILD_CFLAGS += -D__DISABLE_EXPORTS +# 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 -- 2.28.0.402.g5ffc5be6b7-goog