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=-10.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 14E06C433E0 for ; Wed, 15 Jul 2020 08:55:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D96E8206D5 for ; Wed, 15 Jul 2020 08:55:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="REAg+4jM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730055AbgGOIzB (ORCPT ); Wed, 15 Jul 2020 04:55:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56266 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728145AbgGOIzB (ORCPT ); Wed, 15 Jul 2020 04:55:01 -0400 Received: from mail-io1-xd42.google.com (mail-io1-xd42.google.com [IPv6:2607:f8b0:4864:20::d42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 20D2DC061755 for ; Wed, 15 Jul 2020 01:55:01 -0700 (PDT) Received: by mail-io1-xd42.google.com with SMTP id k23so1406542iom.10 for ; Wed, 15 Jul 2020 01:55:01 -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=E2KzDTTFRMDiRWJvyL1sP2xPLBu+h45b96i3t1+zICg=; b=REAg+4jMgFjTriSI5Lb0DMOgace/gsHcOhmNuScsAQpLlZNqocusWWB0jZYfdmjSxP 38l7QutyQ1JxMOQlHKZLh0wI17gFE2diQLmCqTGo00F/QJD2N8xY8Hr6cmS/nTG3iFe2 ElK1iW+HwQhoKoHVP7+a6W4MuY5rb4rVJzF1KRdBhBuQTs6t+xfubC5Ptl7CxjypZ1P4 C0tFFyfZZuSttYWNi+p+kpFEMjCm6elPYU7jq7CvJZUHVjTE+0hzQVQcltD2FrJcnMqy OnPyfIU0IflA0aaqOXFaeiuHmSDMQ8ozB2UNnguweCdAJ18RMhLDOD9SlH1xs8gkVALP G2sQ== 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=E2KzDTTFRMDiRWJvyL1sP2xPLBu+h45b96i3t1+zICg=; b=hT1YZp71qoUezFgoQXKa4YtK3gv10xDe6eSYDo9P7pwwWLpqjCsuPGQ8p8Xd5aeTjI 6cwh0mDylST/CmXZ6N8UUP6L3TeCt/xQ+AudUb1mHxjrp/h72mFxFtLwjzqo6NKrJd+8 4q+okqwDJ8d35mqb0oFqGW320uUciRwTBVLIgBgcEeD79POGNVfqkvTBGAfToepc9QbL h7JFSoAheB5B0iTISSDj/awOz+VfSJjBMWuojWyh3mjDlqXBLSZdWVGd7wMT1EuXZlWj HcEfOHexbhG3nC3yPyb/RRg8mOdUxPKY2mazK6//Hoi2q2J35LT6RYEjNXbLd08kW6e+ 7U9Q== X-Gm-Message-State: AOAM533ztRjkxbs3JK7dE8FmCcG9oVRR9CUM5u474tm4n0Zxop8/KQf8 LXiXAumhnp20FNplM2BV/wyLS3c64RmYyxp/tP4= X-Google-Smtp-Source: ABdhPJz7vNmjqPEigVUxaXZKf2QB7tcA/b2b+Q3C0oB6IQ4cfmzqBcJ5BN8+V+V89TuDMyBt64LqaV1Nd1j4r2f8x0c= X-Received: by 2002:a05:6602:1555:: with SMTP id h21mr8957112iow.163.1594803300431; Wed, 15 Jul 2020 01:55:00 -0700 (PDT) MIME-Version: 1.0 References: <20200714023836.2310569-1-nivedita@alum.mit.edu> <20200715004133.1430068-4-nivedita@alum.mit.edu> In-Reply-To: <20200715004133.1430068-4-nivedita@alum.mit.edu> Reply-To: sedat.dilek@gmail.com From: Sedat Dilek Date: Wed, 15 Jul 2020 10:54:49 +0200 Message-ID: Subject: Re: [PATCH v5 3/7] x86/boot/compressed: Get rid of GOT fixup code 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 , Kees Cook , Nathan Chancellor , Arnd Bergmann , "H . J . Lu" , 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 Wed, Jul 15, 2020 at 2:41 AM Arvind Sankar wrote: > > From: Ard Biesheuvel > > In a previous patch, we have eliminated GOT entries from the decompressor > binary and added an assertion that the .got section is empty. This means > that the GOT fixup routines that exist in both the 32-bit and 64-bit > startup routines have become dead code, and can be removed. > > While at it, drop the KEEP() from the linker script, as it has no effect > on the contents of output sections that are created by the linker itself. > > Reviewed-by: Kees Cook > Signed-off-by: Ard Biesheuvel > Acked-by: Arvind Sankar > Signed-off-by: Arvind Sankar > From: Ard Biesheuvel > Link: https://lore.kernel.org/r/20200523120021.34996-4-ardb@kernel.org Tested-by: Sedat Dilek - Sedat - > --- > arch/x86/boot/compressed/head_32.S | 24 ++--------- > arch/x86/boot/compressed/head_64.S | 57 -------------------------- > arch/x86/boot/compressed/vmlinux.lds.S | 4 +- > 3 files changed, 5 insertions(+), 80 deletions(-) > > diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S > index 03557f2174bf..39f0bb43218f 100644 > --- a/arch/x86/boot/compressed/head_32.S > +++ b/arch/x86/boot/compressed/head_32.S > @@ -49,16 +49,13 @@ > * 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, _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 > - * R_386_32 relocations when relocating the kernel. To generate > - * R_386_RELATIVE relocations, we mark _bss, _ebss, _got, _egot and _end as > - * hidden: > + * _bss, _ebss and _end, in PIE. It isn't wrong, just less optimal than > + * 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, _ebss and _end as hidden: > */ > .hidden _bss > .hidden _ebss > - .hidden _got > - .hidden _egot > .hidden _end > > __HEAD > @@ -192,19 +189,6 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) > shrl $2, %ecx > rep stosl > > -/* > - * Adjust our own GOT > - */ > - leal _got(%ebx), %edx > - leal _egot(%ebx), %ecx > -1: > - cmpl %ecx, %edx > - jae 2f > - addl %ebx, (%edx) > - addl $4, %edx > - jmp 1b > -2: > - > /* > * Do the extraction, and jump to the new kernel.. > */ > diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S > index 97d37f0a34f5..bf1ab30acc5b 100644 > --- a/arch/x86/boot/compressed/head_64.S > +++ b/arch/x86/boot/compressed/head_64.S > @@ -40,8 +40,6 @@ > */ > .hidden _bss > .hidden _ebss > - .hidden _got > - .hidden _egot > .hidden _end > > __HEAD > @@ -353,25 +351,6 @@ SYM_CODE_START(startup_64) > /* Set up the stack */ > leaq boot_stack_end(%rbx), %rsp > > - /* > - * paging_prepare() and cleanup_trampoline() below can have GOT > - * references. Adjust the table with address we are running at. > - * > - * Zero RAX for adjust_got: the GOT was not adjusted before; > - * there's no adjustment to undo. > - */ > - xorq %rax, %rax > - > - /* > - * Calculate the address the binary is loaded at and use it as > - * a GOT adjustment. > - */ > - call 1f > -1: popq %rdi > - subq $1b, %rdi > - > - call .Ladjust_got > - > /* > * At this point we are in long mode with 4-level paging enabled, > * but we might want to enable 5-level paging or vice versa. > @@ -464,21 +443,6 @@ trampoline_return: > pushq $0 > popfq > > - /* > - * Previously we've adjusted the GOT with address the binary was > - * loaded at. Now we need to re-adjust for relocation address. > - * > - * Calculate the address the binary is loaded at, so that we can > - * undo the previous GOT adjustment. > - */ > - call 1f > -1: popq %rax > - subq $1b, %rax > - > - /* The new adjustment is the relocation address */ > - movq %rbx, %rdi > - call .Ladjust_got > - > /* > * Copy the compressed kernel to the end of our buffer > * where decompression in place becomes safe. > @@ -556,27 +520,6 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) > jmp *%rax > SYM_FUNC_END(.Lrelocated) > > -/* > - * Adjust the global offset table > - * > - * RAX is the previous adjustment of the table to undo (use 0 if it's the > - * first time we touch GOT). > - * RDI is the new adjustment to apply. > - */ > -.Ladjust_got: > - /* Walk through the GOT adding the address to the entries */ > - leaq _got(%rip), %rdx > - leaq _egot(%rip), %rcx > -1: > - cmpq %rcx, %rdx > - jae 2f > - subq %rax, (%rdx) /* Undo previous adjustment */ > - addq %rdi, (%rdx) /* Apply the new adjustment */ > - addq $8, %rdx > - jmp 1b > -2: > - ret > - > .code32 > /* > * This is the 32-bit trampoline that will be copied over to low memory. > diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S > index 4bcc943842ab..a4a4a59a2628 100644 > --- a/arch/x86/boot/compressed/vmlinux.lds.S > +++ b/arch/x86/boot/compressed/vmlinux.lds.S > @@ -43,9 +43,7 @@ SECTIONS > _erodata = . ; > } > .got : { > - _got = .; > - KEEP(*(.got)) > - _egot = .; > + *(.got) > } > .got.plt : { > *(.got.plt) > -- > 2.26.2 >