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=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 A086DC2D0A6 for ; Thu, 3 Sep 2020 20:31:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 788D420658 for ; Thu, 3 Sep 2020 20:31:14 +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 S1729408AbgICUbN (ORCPT ); Thu, 3 Sep 2020 16:31:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35490 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729352AbgICUbC (ORCPT ); Thu, 3 Sep 2020 16:31:02 -0400 Received: from mail-qk1-x749.google.com (mail-qk1-x749.google.com [IPv6:2607:f8b0:4864:20::749]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6E86FC061260 for ; Thu, 3 Sep 2020 13:30:57 -0700 (PDT) Received: by mail-qk1-x749.google.com with SMTP id v16so2276415qka.18 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=XoyNi/qlj7QcRbuDlshZFUygUFTTaMoPZB8C3llXECEOMoGw2Ef9UaRS/OOe5B16ul 6ni5AueoITIczzzdXOeImiiLM5Vnk8d2GSRKF8uotaPoyNpNxyEFrCf43z8vHvYg4o6h VrCWVaCjjToigBFCbpoyIu53rIHuGaZrgE/MM+Or1trDJiRFL9pWvPx1cvX83GlCOD/X 0ySmFQcXNK8VMkCcZF8T8fjx+We7uXgbo1wNTE+rHkboMP4KnXGoKjHW2v1B68oJe5OK DMFis8HkW2aTMP8zMRgYJiULYu5O++z1VJDm4M9Qm/DCsTGM30L0qCDqBccZTQ9vtox4 XMWw== X-Gm-Message-State: AOAM533z1SMCM5gjjjdMhpTa3t4lOHdieHoEK1kaE6PQYBcIUq73JjFN yn3lFghBDrq1liWuHLJkn3WIwfuv6bTIRhFA83k= 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-kbuild-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@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