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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=no 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 11080C433DF for ; Mon, 25 May 2020 22:59:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EE8D22071C for ; Mon, 25 May 2020 22:59:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729945AbgEYW7X (ORCPT ); Mon, 25 May 2020 18:59:23 -0400 Received: from mail-qt1-f196.google.com ([209.85.160.196]:33600 "EHLO mail-qt1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725834AbgEYW7W (ORCPT ); Mon, 25 May 2020 18:59:22 -0400 Received: by mail-qt1-f196.google.com with SMTP id e16so8922263qtg.0 for ; Mon, 25 May 2020 15:59:20 -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=nkhs1vMkliVWrepyz3nCPdQswI/d3UMqurs0UD2o4Lc=; b=J0wlypC/yxLo0v2RHdqhJsjY4tRUNUmqT5S+m0VJ0ps0eLEFSKr52h4StPkzP1VH86 DhIwU5kmNcrE8z/SXpDMFBZhbeXDpFTXCOZwThL3rQkjxJAs6QvE8ukgyvzFeHLXiV39 2UW1vFRgVmWLWNgt6h0d8PRk8wqsArBNJxjhlhbkCx9s+GlcNrfkFfLYa2ivlGaWx99J sPckqIXNvNcoJHzXxfarULnrytfGm3K95LvsojhltTd5aklLaN2J60gPyFyyazt/XPpw qIHRLm/6NNobExAF2bZUuJvIqj8XAUpphR3IzGCQ/RcJqO/1OPoAsToFZ1JFNpTMX30J UMjg== X-Gm-Message-State: AOAM531jYc2GELt4oRRDXGMbxp3Jba5/lelyJl+C0HXgHVFa2yCtuows cbEjo24oOOujoOqrVnTxeQg= X-Google-Smtp-Source: ABdhPJwemMCpixd/VkVsZpPjyun6nr8KM9JhDlrnpvWkKxuXa2chSkOpg5pHB8lvcIdb3Yv9qIYE4g== X-Received: by 2002:ac8:543:: with SMTP id c3mr29290586qth.8.1590447560082; Mon, 25 May 2020 15:59:20 -0700 (PDT) Received: from rani.riverdale.lan ([2001:470:1f07:5f3::b55f]) by smtp.gmail.com with ESMTPSA id d140sm15024585qkc.22.2020.05.25.15.59.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 25 May 2020 15:59:19 -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 , linux-kernel@vger.kernel.org Subject: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel Date: Mon, 25 May 2020 18:59:14 -0400 Message-Id: <20200525225918.1624470-1-nivedita@alum.mit.edu> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200524212816.243139-1-nivedita@alum.mit.edu> References: <20200524212816.243139-1-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 The compressed kernel currently contains bogus runtime relocations in the startup code in head_{32,64}.S, which are generated by the linker, but must not actually be processed at runtime. This generates warnings when linking with the BFD linker, and errors with LLD, which defaults to erroring on runtime relocations in read-only sections. It also requires the -z noreloc-overflow hack for the 64-bit kernel, which prevents us from linking it as -pie on an older BFD linker (<= 2.26) or on LLD, because the locations that are to be apparently relocated are only 32-bits in size and so cannot normally have R_X86_64_RELATIVE relocations. This series aims to get rid of these relocations. It is based on efi/next, where the latest patches touch the head code to eliminate the global offset table. The first patch is an independent fix for LLD, to avoid an orphan section in arch/x86/boot/setup.elf. The second patch gets rid of almost all the relocations. It uses standard PIC addressing technique for 32-bit, i.e. loading a register with the address of _GLOBAL_OFFSET_TABLE_ and then using GOTOFF references to access variables. For 64-bit, there is 32-bit code that cannot use RIP-relative addressing, and also cannot use the 32-bit method, since GOTOFF references are 64-bit only. This is instead handled using a macro to replace a reference like gdt with (gdt-startup_32) instead. The assembler will generate a PC32 relocation entry, with addend set to (.-startup_32), and these will be replaced with constants at link time. This works as long as all the code using such references lives in the same section as startup_32, i.e. in .head.text. The third patch addresses a remaining issue with the BFD linker, which insists on generating runtime relocations for absolute symbols. We use z_input_len and z_output_len, defined in the generated piggy.S file, as symbols whose absolute "addresses" are actually the size of the compressed payload and the size of the decompressed kernel image respectively. LLD does not generate relocations for these two symbols, but the BFD linker does, prior to the upcoming 2.35. To get around this, piggy.S is extended to also define two u32 variables (in .rodata) with the lengths, and the head code is modified to use those instead of the symbol addresses. An alternative way to handle z_input_len/z_output_len would be to just include piggy.S in head_{32,64}.S instead of as a separate object file, since the GNU assembler doesn't generate relocations for symbols set to constants. The last patch adds a check in the linker script to ensure that no runtime relocations get reintroduced. Since the GOT has been eliminated as well, the compressed kernel has no runtime relocations whatsoever any more. Changes from v1: - Add .text.* to setup.ld instead of just .text.startup - Rename the la() macro introduced in the second patch for 64-bit to rva(), and rework the explanatory comment. - In the last patch, check both .rel.dyn and .rela.dyn, instead of just one per arch. Arvind Sankar (4): x86/boot: Add .text.* to setup.ld x86/boot: Remove run-time relocations from .head.text code x86/boot: Remove runtime relocations from head_{32,64}.S x86/boot: Check that there are no runtime relocations arch/x86/boot/compressed/Makefile | 36 +-------- arch/x86/boot/compressed/head_32.S | 59 +++++++------- arch/x86/boot/compressed/head_64.S | 108 +++++++++++++++---------- arch/x86/boot/compressed/mkpiggy.c | 6 ++ arch/x86/boot/compressed/vmlinux.lds.S | 8 ++ arch/x86/boot/setup.ld | 2 +- 6 files changed, 115 insertions(+), 104 deletions(-) -- 2.26.2