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 E1CCBC433E0 for ; Tue, 26 May 2020 12:44:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B696C207CB for ; Tue, 26 May 2020 12:44:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="d4oVsmlS" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389290AbgEZMom (ORCPT ); Tue, 26 May 2020 08:44:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58548 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389265AbgEZMol (ORCPT ); Tue, 26 May 2020 08:44:41 -0400 Received: from mail-il1-x141.google.com (mail-il1-x141.google.com [IPv6:2607:f8b0:4864:20::141]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6E853C03E96D for ; Tue, 26 May 2020 05:44:41 -0700 (PDT) Received: by mail-il1-x141.google.com with SMTP id l20so20147688ilj.10 for ; Tue, 26 May 2020 05:44:41 -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=192v8HLLXNUx+tzLmNUVYrYxDcyonvfeueAArNuXXsI=; b=d4oVsmlSAyr8eSxp3bZQn6iMXwXt9As6p8lp8pWw+ZfV4MJ+GOit/1KDMg26e5uKBO n7qmpMF2eyBRJ6DgSAq/ZbAJZAZC3Yfe8gUOnpgzE75HWZ9hEjRLp6kABtZwh1kYWAum zwE9Cb37lamzylUEcJ6O6SF9I48LxlXmmcWcXo2NKZHz4mmyu/5zY/WTfNAsg26qzut8 QybUjo0eYL233a/cBrJOXOXhHY9cVqU0LoQZO67qrWZhugOJv2NB/KM3fJfRBqJhJfIW dnvbh/Qa6tiILM4AZ+SbvU/F45KoSHeRnr5LbpjcwlsprV+Z8fpxgyhW6rjgDDCbF99w jGmA== 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=192v8HLLXNUx+tzLmNUVYrYxDcyonvfeueAArNuXXsI=; b=k8h87MAjgu9hBiZc/5Vt8Bwcx9nUKDBbgdcT1uYScnyLXs4Yc9pemfB94UxoPzR6ue hVQBYMYbq7hpyiiAdhWSy4aUjb0lnu1K8YjJur0w7Nb3f8JPKcG5w1v26jSWV/923+mo OQZ4+5bwYU/PvoaU0XKAjkbUy4dRnUZxcULCYi6rCpy/TBdyUnYjTHrT1U0VHVBweHrl UC2M+DEzHZXwqbvbwzvDMDJ65+b0CVrHZdtH6YY/WKs6cwPDq7mPsXj1Ss9eUlbufJj4 MJiCO6Fmq8XNe/eTLHDAgdzHBG9us2LknM+Vfy4SgxvAupEDQQ3gNm/L/xI+CsNSX/fC X0GQ== X-Gm-Message-State: AOAM5325obqIP6T7PGjzSvm7XnaXJuv+p/EfwjD1enROxnLpoW6PdcQH SF1BUItXvx94gUabMAeonz/986Cz2cVDs7jN4dY= X-Google-Smtp-Source: ABdhPJwdgN5kiESZs1KmJ2NKBxJ2BXz03Qx/L16bIcWrHQAa+xF5Go3ubIfVfYgz2sWkygjp8HDCUBdJODKWVurYiA0= X-Received: by 2002:a92:6608:: with SMTP id a8mr934770ilc.204.1590497080697; Tue, 26 May 2020 05:44:40 -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 14:44:29 +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 2:33 PM Sedat Dilek wrote: > > 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 - Are those diffs correct when using "x86/boot: Correct relocation destination on old linkers"? $ cat ../head_32_S.diff diff --cc arch/x86/boot/compressed/head_32.S index 064e895bad92,03557f2174bf..000000000000 --- a/arch/x86/boot/compressed/head_32.S +++ b/arch/x86/boot/compressed/head_32.S @@@ -49,13 -49,17 +49,14 @@@ * Position Independent Executable (PIE) so that linker won't optimize * R_386_GOT32X relocation to its fixed symbol address. Older * linkers generate R_386_32 relocations against locally defined symbols, - * _bss, _ebss, in PIE. It isn't wrong, just suboptimal compared - * _bss, _ebss, _got, _egot and _end, in PIE. It isn't wrong, just less - * optimal than R_386_RELATIVE. But the x86 kernel fails to properly handle ++ * _bss, _ebss, _end in PIE. It isn't wrong, just suboptimal compared + * to R_386_RELATIVE. But the x86 kernel fails to properly handle * R_386_32 relocations when relocating the kernel. To generate - * R_386_RELATIVE relocations, we mark _bss and _ebss as hidden: - * R_386_RELATIVE relocations, we mark _bss, _ebss, _got, _egot and _end as - * hidden: ++ * R_386_RELATIVE relocations, we mark _bss, _ebss and _end as hidden: */ .hidden _bss .hidden _ebss - .hidden _got - .hidden _egot + .hidden _end __HEAD SYM_FUNC_START(startup_32) $ cat ../head_64_S.diff diff --cc arch/x86/boot/compressed/head_64.S index 4b7ad1dfbea6,76d1d64d51e3..000000000000 --- a/arch/x86/boot/compressed/head_64.S +++ b/arch/x86/boot/compressed/head_64.S @@@ -40,34 -40,11 +40,35 @@@ */ .hidden _bss .hidden _ebss - .hidden _got - .hidden _egot + .hidden _end __HEAD + +/* + * This macro gives the relative virtual address of X, i.e. the offset of X + * from startup_32. This is the same as the link-time virtual address of X, + * since startup_32 is at 0, but defining it this way tells the + * assembler/linker that we do not want the actual run-time address of X. This + * prevents the linker from trying to create unwanted run-time relocation + * entries for the reference when the compressed kernel is linked as PIE. + * + * A reference X(%reg) will result in the link-time VA of X being stored with + * the instruction, and a run-time R_X86_64_RELATIVE relocation entry that + * adds the 64-bit base address where the kernel is loaded. + * + * Replacing it with (X-startup_32)(%reg) results in the offset being stored, + * and no run-time relocation. + * + * The macro should be used as a displacement with a base register containing + * the run-time address of startup_32 [i.e. rva(X)(%reg)], or as an immediate + * [$ rva(X)]. + * + * This macro can only be used from within the .head.text section, since the + * expression requires startup_32 to be in the same section as the code being + * assembled. + */ +#define rva(X) ((X) - startup_32) + .code32 SYM_FUNC_START(startup_32) /* Thanks. - Sedat -