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 5C78EC433E0 for ; Tue, 26 May 2020 12:34:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 36776207CB for ; Tue, 26 May 2020 12:34:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Kmztc0PZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389107AbgEZMeH (ORCPT ); Tue, 26 May 2020 08:34:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56912 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389007AbgEZMeH (ORCPT ); Tue, 26 May 2020 08:34:07 -0400 Received: from mail-io1-xd43.google.com (mail-io1-xd43.google.com [IPv6:2607:f8b0:4864:20::d43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EAB04C03E96D for ; Tue, 26 May 2020 05:34:06 -0700 (PDT) Received: by mail-io1-xd43.google.com with SMTP id q8so20326497iow.7 for ; Tue, 26 May 2020 05:34:06 -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=dKMQLkfxGfTGmxyabfuv0+iSbqh28h3pHwoaw3c28Js=; b=Kmztc0PZHeE9GMnh+mwlwAKwSVOZM0qFkahHHiT4oXMnwmxdAc84Z55hM4XpZekikt yjZueHv8cSsjfF3oOSdK9BfSBr3ZkVUmQO5Fe47BHw7a43OJwJqX72qOsfFHIXPrN0Ux l/RouRFmj91hidG2L/LurQeeJSzvX5AJs3q0/+sFZT2ECOiSvz8YEdWlmu2QB9MCXGv5 PTHOaTyE2u82FCyb3m4BEnITzt712SFrrBQ7SIaf4zwOjFU9agaGcyhI0i0UVoWczXGx CSr/6JTKLXRyZDBZlKcChrXkSpOtlIbK3DGvtvuhv3LWypi9O+eF4jKnRJsvH+ZH3Mbo U4+w== 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=dKMQLkfxGfTGmxyabfuv0+iSbqh28h3pHwoaw3c28Js=; b=RfCOXRjfjX6diW2U6V3QOSwDnt4CmN8sx7z2TCLCSCE/HCVWifrF2zF1fWgeeCJoig 65Q07gIHAXb3F9sEpeG9lw3UH0ZuNBBIPyPxlZvwuLUAmHtA1nWA9rOb6m/y2Sr59LHT ODGXEfMYCvZx6eRUklRc3S5Lm7enEvQopqcFFuxmrSz0L1TQ91RP3JIzg8zYoStP+8A+ 2SQM/SOevSxuQIe6RvSIhCfTExi7GK6YjaScdtoPbVybC3Gq8zE05bABRBg4IlE+VzBD UGaYl/NM+oG7OMtc61gTg1txPEu+HYAgyWEjF1TRjpGlwuCwIvmEI1d20mGQq9Uvnx03 /x3A== X-Gm-Message-State: AOAM531WIHULKBgjc4I37K/Ke6NU5y0RLM6h6J4OSGpBrkyJ6lnaL/V2 YdKxmtKXOoRJ/4faulpNU9Jy3q8ke5RUdg+RilY= X-Google-Smtp-Source: ABdhPJyuM1Q8Q41Q9x5fahY7RImPuyJ7v5KqrUC9qphA29v7YRe+UbZ+AgPiUR2BFKQ28wSlv3DqMorPuhNHt3sDVxE= X-Received: by 2002:a02:a408:: with SMTP id c8mr744385jal.125.1590496446177; Tue, 26 May 2020 05:34:06 -0700 (PDT) MIME-Version: 1.0 References: <20200524212816.243139-1-nivedita@alum.mit.edu> <20200525225918.1624470-1-nivedita@alum.mit.edu> In-Reply-To: Reply-To: sedat.dilek@gmail.com From: Sedat Dilek Date: Tue, 26 May 2020 14:33:55 +0200 Message-ID: Subject: Re: [PATCH v2 0/4] x86/boot: Remove runtime relocations from compressed kernel To: Ard Biesheuvel Cc: Arvind Sankar , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , X86 ML , Nick Desaulniers , Fangrui Song , Dmitry Golovin , Clang-Built-Linux ML , Masahiro Yamada , Daniel Kiper , Linux Kernel Mailing List 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 2:30 PM Ard Biesheuvel wrote: > > On Tue, 26 May 2020 at 14:29, Sedat Dilek wrote: > > > > 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? > > > > efi/next is here: > > https://git.kernel.org/pub/scm/linux/kernel/git/efi/efi.git/log/?h=next > > You'll need the top 3 patches. Thanks /o\. - Sedat -