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: 11786037 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 5BB1092C for ; Fri, 18 Sep 2020 20:15:17 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 618DB2311C for ; Fri, 18 Sep 2020 20:15:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="kS9nJccC" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 618DB2311C Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-19919-patchwork-kernel-hardening=patchwork.kernel.org@lists.openwall.com Received: (qmail 13675 invoked by uid 550); 18 Sep 2020 20:14:57 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 13575 invoked from network); 18 Sep 2020 20:14:57 -0000 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=IUrrE+G3kdvK94c4E+l2bKzDZqKDsSZOvMvxu0f8+0bpkmrnsHGULKfwM0TuUN+Y/G cJJaj7fCHB/pXx+yBx0wfAGYWHWD+L4hvnbhB+QDufnYw1vkdBqD4mVXXGG5M7npRROQ 878bMNz14MRzeWjO7k+zYUinVfB1YK4pZp0BEqTtM5ZAQ0UWRb8uIgFMW2GibQgFfPow Hetckyy7ygCXYB5A2vmV7z1FRrUw3d93ZITxYZm/ZIz58H+BB95rpVx7yrk+8CmN0RCl XIS9uOdQhT61lMiAZK+WzfLK5Z0PrF4lv5vyJIm9uJBOWLdK9LvQ4R493f3Rs9n9huO+ fv+g== X-Gm-Message-State: AOAM532xVPHUmcW5igc3vWwKRQHMY6xLbWwsGVzt0P1pRCayrip2HEl0 wh3cyY9SIXw0fs/XuNFjw1Qz7LisInwfT2BCJy4= 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 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