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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=no 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 E1D91C3815B for ; Wed, 15 Apr 2020 08:41:36 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9532620784 for ; Wed, 15 Apr 2020 08:41:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="DCWmmaix"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="U/2uDTJR" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9532620784 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=KSLYe1p1GfML6ubqhYfIEYLQODqe3tSoKPDIjTG7Axw=; b=DCWmmaixaYARF6 5NAQHABu8t2A8pYdM2fOXmrRiS6xIYrM9q0FhOz406sTISlr28LL9V73NfxSWjvLqxTpYHyCxpKOv gWHkcOO/CFRtjS3UyTQfxKOIAehemyhbchnNgErVLXLI2iZCqaw8KEQ0oqY744SY65nEJawQh6+m8 ijOJvuY15Hlo7jdi04ofzHmVVk57iS+rMz6uhsMAAHwfXlcl3hQ6tLVz7rT+wFQTpusPPeA7hS8MR /MB1tk0y0XG4vqnyfm58M4YA001s+KdJhjCGKWqVRRBCZWyWQRUPwgeDOcgKiEiyonbYCn8hQHdzm DRzJGjEJ2HDbwddFGm6w==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jOdby-00077X-BW; Wed, 15 Apr 2020 08:41:34 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jOdZa-0002RT-KM for linux-arm-kernel@lists.infradead.org; Wed, 15 Apr 2020 08:39:08 +0000 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 53C5F20784; Wed, 15 Apr 2020 08:39:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586939945; bh=vgNL0nmxrNPZ77iSc+eqLDS1hNmohky3P8MkxPGmAFA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=U/2uDTJR7FC0k32qoEiGioaWSwb1ZZWOJ9hs8ZtYeWAFOHNFWRXjQDsw3r2cccbU/ 27jZ6EIUfis7cAXG/AcJfLg0x2+lpN49155UspngL+DW+aLwR03YQx8JA6TDSWT8r5 F5a3WwG1lahUmy6ccF0Susi1Ab+JbcBQ6rQGbUuI= Date: Wed, 15 Apr 2020 09:39:00 +0100 From: Will Deacon To: Ard Biesheuvel Subject: Re: [PATCH] arm64: set TEXT_OFFSET to 0x0 in preparation for removing it entirely Message-ID: <20200415083900.GA12621@willie-the-truck> References: <20200415082922.32709-1-ardb@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200415082922.32709-1-ardb@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200415_013906_705237_E2C0FE04 X-CRM114-Status: GOOD ( 16.75 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, catalin.marinas@arm.com, james.morse@arm.com, linux-arm-kernel@lists.infradead.org, suzuki.poulose@arm.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Apr 15, 2020 at 10:29:22AM +0200, Ard Biesheuvel wrote: > TEXT_OFFSET on arm64 is a historical artifact from the early days of > the arm64 port where the boot protocol was basically 'copy this image > to the base of memory + 512k', giving us 512 KB of guaranteed BSS space > to put the swapper page tables. When the arm64 port was merged for > v3.10, the Image header already carried the actual value of TEXT_OFFSET, > to allow the bootloader to discover it dynamically rather than hardcode > it to 512 KB. Hey, we're older than that! (3.7) > Today, this memory window is not used for any particular purpose, and > it is simply handed to the page allocator at boot. The only reason it > still exists is because of the 512k misalignment it causes with respect > to the 2 MB aligned virtual base address of the kernel, which affects > the virtual addresses of all statically allocated objects in the kernel > image. > > However, with the introduction of KASLR in v4.6, we added the concept of > relocatable kernels, which rewrite all absolute symbol references at > boot anyway, and so the placement of such kernels in the physical address > space is irrelevant, provided that the minimum segment alignment is > honoured (64 KB in most cases, 128 KB for 64k pages kernels with vmap'ed > stacks enabled). This makes 0x0 and 512 KB equally suitable values for > TEXT_OFFSET on the off chance that we are dealing with boot loaders that > ignore the value passed via the header entirely. > > Considering that the distros as well as Android ship KASLR-capable > kernels today, and the fact that TEXT_OFFSET was discoverable from the > Image header from the very beginning, let's change this value to 0x0, in > preparation for removing it entirely at a later date. Can we kill CONFIG_ARM64_RANDOMIZE_TEXT_OFFSET at the same time please? It seems less useful now than ever and it would move us closer to removing the TEXT_OFFSET definition entirely (but maybe we should wait a couple of cycles before doing that... what do you reckon?). Cheers, Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel