From patchwork Fri Sep 18 20:14:09 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sami Tolvanen X-Patchwork-Id: 1367289 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=23.128.96.18; helo=vger.kernel.org; envelope-from=linux-pci-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=google.com header.i=@google.com header.a=rsa-sha256 header.s=20161025 header.b=kS9nJccC; dkim-atps=neutral Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 4BtQ6p0jrCz9sTS for ; Sat, 19 Sep 2020 06:14:58 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726241AbgIRUOr (ORCPT ); Fri, 18 Sep 2020 16:14:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52732 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726354AbgIRUOq (ORCPT ); Fri, 18 Sep 2020 16:14:46 -0400 Received: from mail-yb1-xb4a.google.com (mail-yb1-xb4a.google.com [IPv6:2607:f8b0:4864:20::b4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E5FB6C0613D9 for ; Fri, 18 Sep 2020 13:14:45 -0700 (PDT) Received: by mail-yb1-xb4a.google.com with SMTP id f185so6637881ybf.17 for ; Fri, 18 Sep 2020 13:14:45 -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=QG37uO1d4USzrK2i79mol19BZHF3voEs5YXCH0vFDXg=; b=kS9nJccCRITkbrAyCK9Hc7v1LETkgjrZzbCI78fOJk9GspwsE0lD6AsMWWG9e/Ya6w kQ7OAgO+NsJbiNEURN/xqwJc+nMm2JlmzicPoqTkbkTgYLChVmHJmFrbVcTMgiIM1LfM AMIn2fwD4sdTg9b5RFBa3v7hPzAOv72tQhHG2zedzbaGOgS5AllQnoGhiut1jy6gfUPb IHOl5kVpEYZmlx3J300NFEalCTngIq2wdGL7A0LMMidJtwteLyUB84t3JQdj/BGr11/r XP03Hd7VXorIrHoqHnVpAgFdqejQhRQlU/QiTZkkxeCP6z2bKBR11111wx5Cdsjef2hw h1Og== 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=QG37uO1d4USzrK2i79mol19BZHF3voEs5YXCH0vFDXg=; b=HcVHmZAxdSeo/Obnvd6/kRnClRwCDdvpMqzh5DmM0WPRq1h1zlhOOvCRHjeU2WYaK3 lIdTDm6ytLToFFf2ihnYfdH8V8CmNrZ7m3par+liiDIWQpjUEYeMZN/tewLVcaa0+X5e FxIM4f7bYgg73bs9IRXAwyxdzxFYS/i3fa/Qc14zhcZs67mOvhWQVoKXVteGq82vIo0i w4re6ufQCFWN3sJwfa61dYr97pwdSsK5PBRKxYFjtlOX4leqXrz++ggzTf9yevN/yKsJ Kl5p2ryJFC6CeRwmptetf4NaxqXNR/vbs12qTp5xb6i9AGeo7EV23H3b2QCq9dCcuKXg IO/g== X-Gm-Message-State: AOAM532qSSHdJPuuT2XEbWijOePAT27sThGvRaEHO7Gq61f0w5+yIC+a /qxMEx8+neUJuXO5Ptqxwvy0o2EXqbMR1kp9apk= X-Google-Smtp-Source: ABdhPJxOIBe5IUGDSTHVDRZfdndNloI1irNa0De5LGLJBg+ujXNg2cTfcMKCeIjDmjymnjpy+o5CvxVSn10XK63j+fc= Sender: "samitolvanen via sendgmr" X-Received: from samitolvanen1.mtv.corp.google.com ([2620:15c:201:2:f693:9fff:fef4:1b6d]) (user=samitolvanen job=sendgmr) by 2002:a25:3744:: with SMTP id e65mr19951166yba.275.1600460085079; Fri, 18 Sep 2020 13:14:45 -0700 (PDT) Date: Fri, 18 Sep 2020 13:14:09 -0700 In-Reply-To: <20200918201436.2932360-1-samitolvanen@google.com> Message-Id: <20200918201436.2932360-4-samitolvanen@google.com> Mime-Version: 1.0 References: <20200918201436.2932360-1-samitolvanen@google.com> X-Mailer: git-send-email 2.28.0.681.g6f77f65b4e-goog Subject: [PATCH v3 03/30] 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 Precedence: bulk List-ID: X-Mailing-List: linux-pci@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