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=-5.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS 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 055C7C433DF for ; Tue, 26 May 2020 12:29:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CE4072084C for ; Tue, 26 May 2020 12:29:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="RUDwiQ8S" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389012AbgEZM3m (ORCPT ); Tue, 26 May 2020 08:29:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56220 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728195AbgEZM3k (ORCPT ); Tue, 26 May 2020 08:29:40 -0400 Received: from mail-io1-xd41.google.com (mail-io1-xd41.google.com [IPv6:2607:f8b0:4864:20::d41]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 21862C03E96D for ; Tue, 26 May 2020 05:29:40 -0700 (PDT) Received: by mail-io1-xd41.google.com with SMTP id d7so21739831ioq.5 for ; Tue, 26 May 2020 05:29:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:reply-to:from:date:message-id :subject:to:cc; bh=PHdiDb5Mr94WWWQ3Mnyn3fpsR2uXfxFeRBM2541NcjE=; b=RUDwiQ8S/8SJMjtICUN/A7+hhlOyeFxe4X2MJc6ughX1N2Mqe5tRaN2sstGPyfaZW8 wOn8sOrmTMwEsWfWs7C6J03EKDFVg/6wSfSZ57LMIpZsDxRdLU6R4FVV7eiU1dt0PfM2 YW61zSmNzmnpkAAf7GV0vOvFLGryVmQ0xkoE0Uor9rIlMFyjc9/MdBhOX9PeDfnvEEne En4ykExbAHKQ1EKQ/OAQshQu1XeGFP5e3BaiUxxHxtEWQ21burD+cFW/aKTHii2Aky9Y yOi3JsoYDLu4coL758Wyiwis3KJ2F1w5TRrQQftO0xLHwDOKzRSJpj+4XrcHOUaejNlL yHxg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:reply-to :from:date:message-id:subject:to:cc; bh=PHdiDb5Mr94WWWQ3Mnyn3fpsR2uXfxFeRBM2541NcjE=; b=Q56dnG8JBM/QB8rfjHiBczaXeV9yaQLG26E3OkmHTLzE/1Q+9BRx0gUiu4JYdRsJ12 QG7qruO8AsHkFyNVKuqw29SCYFwhoyO9vnxwTAxi4Oxz7tW5a7VJZJI8BFRYkdisJsvj Ciou94aKzusAerBYwi8wvhxiRGy8lXSX7K3PyBffJrME5B4TQoWYdhkDwPY3MKE/z0Ui qz9JQLR3QWzrgUVqKh96jOSoFgBgxLGZ3hNtrDmqiSxVy5B60SBLBnb44BNKVl4ysyJp Bn1vAs5i3/0RwBl0uRHt2qqJh7ow16j9qOZ4tbCBh0+Zl2HwG1eolw2NqecU7clcUomM dKRw== X-Gm-Message-State: AOAM531P71uBlEw9IXQlTCG/jk+g5fpI1Y8tDFCpR5c3hFWvT8btq1LX JRJG4NWKJa3Tmb+Udb0m60GvrdUMsTtj/QzJ/qk= X-Google-Smtp-Source: ABdhPJz092CIn1swlaEjty8qDGM37LW/qzCfFW8c6juBp/HbDtGs8w1WFdbgXt1AwenZDkdOvZUIHxM4oaePLV1NVAc= X-Received: by 2002:a02:ca18:: with SMTP id i24mr742148jak.70.1590496177978; Tue, 26 May 2020 05:29:37 -0700 (PDT) MIME-Version: 1.0 References: <20200524212816.243139-1-nivedita@alum.mit.edu> <20200525225918.1624470-1-nivedita@alum.mit.edu> In-Reply-To: <20200525225918.1624470-1-nivedita@alum.mit.edu> Reply-To: sedat.dilek@gmail.com From: Sedat Dilek Date: Tue, 26 May 2020 14:29:27 +0200 Message-ID: Subject: Re: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel To: Arvind Sankar Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , x86@kernel.org, Nick Desaulniers , Fangrui Song , Dmitry Golovin , Clang-Built-Linux ML , Ard Biesheuvel , Masahiro Yamada , Daniel Kiper , linux-kernel@vger.kernel.org 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 On Tue, May 26, 2020 at 12:59 AM Arvind Sankar wrote: > > 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. > Hi, I would like to test this patchset v2 on top of Linux v5.7-rc7 together with: [1] x86/boot: Discard .discard.unreachable for arch/x86/boot/compressed/vmlinux [2] x86/boot: Correct relocation destination on old linkers I tried to pull efi/next on top of Linux v5.7-rc7 and cleaned up the merge problems, but I am not sure I did it correctly. So, which patches are really relevant from efi/next? What's your suggestions? Regards, - Sedat - [1] https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/patch/?id=d6ee6529436a15a0541aff6e1697989ee7dc2c44 [2] https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/patch/?id=5214028dd89e49ba27007c3ee475279e584261f0 > 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 > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20200525225918.1624470-1-nivedita%40alum.mit.edu.