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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 F3DF1C00523 for ; Wed, 8 Jan 2020 10:23:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CAED12077B for ; Wed, 8 Jan 2020 10:23:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578478992; bh=wCfg2ssSFutFVGkbtoCVz2iPKb67wYGKG6IyCNR1lyQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Mb/xL2mCLCVq/muzR8ZQsdAkHVwufADq/5i7b82FQluwnnaVb1xGK0q4YI5izYP5a PLlm4+yodCLvl/dMqsZQwR2WRh48iGXQuD/brKvhUWiTr0JrB4m4RHgisrp/ohAy/d hdXFbKIsh/bN2zwt3lZyzbEuDIkvV4iES9GJgdTY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727595AbgAHKXM (ORCPT ); Wed, 8 Jan 2020 05:23:12 -0500 Received: from mail.kernel.org ([198.145.29.99]:49694 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726144AbgAHKXM (ORCPT ); Wed, 8 Jan 2020 05:23:12 -0500 Received: from localhost.localdomain (amontpellier-657-1-18-247.w109-210.abo.wanadoo.fr [109.210.65.247]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EDA4A2082E; Wed, 8 Jan 2020 10:23:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578478991; bh=wCfg2ssSFutFVGkbtoCVz2iPKb67wYGKG6IyCNR1lyQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=1qTg2IkYhepZw5OIwlGyLiL1eS1lQVkc5XJ2gP82L0KG5WHcG47/cHlVzaYzkKxYu VaUSbQxS8dPE9aZi/C+uZZI9dOHdutpN9FCHMc1aX7O+9icPM29hzhaJQmvEEDnOci c/K8+Fi/fIP8e1lUJK+/bD/N76vL5z+kKGHZz50Y= From: Ard Biesheuvel To: linux-efi@vger.kernel.org Cc: x86@kernel.org, luto@kernel.org, linux-kernel@vger.kernel.org, Ard Biesheuvel , Maarten Lankhorst , Linus Torvalds , Arvind Sankar Subject: [RFC PATCH 1/3] x86/boot/compressed: move .got.plt entries out of the .got section Date: Wed, 8 Jan 2020 11:23:02 +0100 Message-Id: <20200108102304.25800-2-ardb@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200108102304.25800-1-ardb@kernel.org> References: <20200108102304.25800-1-ardb@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-efi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-efi@vger.kernel.org The .got.plt section contains the part of the GOT which is used by PLT entries, and which gets updated lazily by the dynamic loader when function calls are dispatched through those PLT entries. On fully linked binaries such as the kernel proper or the decompressor, this never happens, and so in practice, the .got.plt section consists only of the first 3 magic entries that are meant to point at the _DYNAMIC section and at the fixup routine in the loader. However, since we don't use a dynamic loader, those entries are never populated or used. This means that treating those entries like ordinary GOT entries, and fixing them up based on the actual placement of the executable in memory is completely pointless, and we can just ignore the .got.plt section entirely, provided that it has no additional entries beyond the first 3 ones. So add an assertion in the linker script to ensure that this assumption holds, and move the contents out of the [_got, _egot) memory range that is modified by the GOT fixup routines. Signed-off-by: Ard Biesheuvel --- arch/x86/boot/compressed/vmlinux.lds.S | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S index 508cfa6828c5..51ca654e43a9 100644 --- a/arch/x86/boot/compressed/vmlinux.lds.S +++ b/arch/x86/boot/compressed/vmlinux.lds.S @@ -44,10 +44,13 @@ SECTIONS } .got : { _got = .; - KEEP(*(.got.plt)) KEEP(*(.got)) _egot = .; } + .got.plt : { + KEEP(*(.got.plt)) + } + .data : { _data = . ; *(.data) @@ -74,3 +77,11 @@ SECTIONS . = ALIGN(PAGE_SIZE); /* keep ZO size page aligned */ _end = .; } + +#ifdef CONFIG_X86_64 +ASSERT (SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18, + "Unexpected GOT/PLT entries detected!") +#else +ASSERT (SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0xc, + "Unexpected GOT/PLT entries detected!") +#endif -- 2.20.1