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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 1FEDCC43441 for ; Sun, 11 Nov 2018 23:58:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E77AD20839 for ; Sun, 11 Nov 2018 23:58:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E77AD20839 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zytor.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732755AbeKLJtK convert rfc822-to-8bit (ORCPT ); Mon, 12 Nov 2018 04:49:10 -0500 Received: from terminus.zytor.com ([198.137.202.136]:54481 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732407AbeKLJtJ (ORCPT ); Mon, 12 Nov 2018 04:49:09 -0500 Received: from wld62.hos.anvin.org (c-24-5-245-234.hsd1.ca.comcast.net [24.5.245.234] (may be forged)) (authenticated bits=0) by mail.zytor.com (8.15.2/8.15.2) with ESMTPSA id wABNwNnL3444911 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NO); Sun, 11 Nov 2018 15:58:24 -0800 Date: Sun, 11 Nov 2018 15:58:16 -0800 User-Agent: K-9 Mail for Android In-Reply-To: <685b425b-c816-4f65-3393-b48e59d170d8@suse.com> References: <20181010061456.22238-1-jgross@suse.com> <20181010061456.22238-3-jgross@suse.com> <685b425b-c816-4f65-3393-b48e59d170d8@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Subject: Re: PLEASE REVERT URGENTLY: Re: [PATCH v5 2/3] x86/boot: add acpi rsdp address to setup_header To: Juergen Gross , linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org, linux-doc@vger.kernel.org CC: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, corbet@lwn.net, boris.ostrovsky@oracle.com From: hpa@zytor.com Message-ID: <9A44B94A-AEDC-4638-A8FF-DEE76FE34056@zytor.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On November 10, 2018 7:22:29 AM PST, Juergen Gross wrote: >On 09/11/2018 23:23, H. Peter Anvin wrote: >> I just noticed this patch -- I missed it because the cover message >> seemed far more harmless so I didn't notice this change. >> >> THIS PATCH IS FATALLY WRONG AND NEEDS TO BE IMMEDIATELY REVERTED >BEFORE >> ANYONE STARTS RELYING ON IT; IT HAS THE POTENTIAL OF BREAKING THE >> BOOTLOADER PROTOCOL FOR ALL FUTURE. >> >> It seems to be based on fundamental misconceptions about the various >> data structures in the protocol, and does so in a way that completely >> breaks the way the protocol is designed to work. >> >> The protocol is specifically designed such that fields are not >version >> dependencies. The version number is strictly to inform the boot >loader >> about which capabilities the kernel has, so that the boot loader can >> know if a certain data field is meaningful and/or honored. >> >>> +Protocol 2.14: (Kernel 4.20) Added acpi_rsdp_addr holding the >physical >>> + address of the ACPI RSDP table. >>> + The bootloader updates version with: >>> + 0x8000 | min(kernel-version, bootloader-version) >>> + kernel-version being the protocol version supported by >>> + the kernel and bootloader-version the protocol version >>> + supported by the bootloader. >> >> [...] >> >>> **** MEMORY LAYOUT >>> >>> The traditional memory map for the kernel loader, used for Image or >>> @@ -197,6 +209,7 @@ Offset Proto Name Meaning >>> 0258/8 2.10+ pref_address Preferred loading address >>> 0260/4 2.10+ init_size Linear memory required during initialization >>> 0264/4 2.11+ handover_offset Offset of handover entry point >>> +0268/8 2.14+ acpi_rsdp_addr Physical address of RSDP table >> >> NO. >> >> That is not how struct setup_header works, nor does this belong here. >> >> struct setup_header contains *initialized data*, and has a length >byte >> at offset 0x201. The bootloader is responsible for copying the full >> structure into the appropriate offset (0x1f1) in struct boot_params. >> >> The length byte isn't actually a requirement, since the maximum >possible >> size of this structure is 144 bytes, and the kernel will (obviously) >not >> look at the older fields anyway, but it is good practice. The kernel >or >> any other entity is free to zero out the bytes past this length >pointer. >> >> There are only 24 bytes left in this structure, and this would occupy >8 >> of them for no valid reason. The *only* valid reason to put a >> zero-initialized field in struct setup_header is if it used by the >> 16-bit legacy BIOS boot, which is obviously not the case here. >> >> This field thus belongs in struct boot_params, not struct >setup_header. > >Would you be okay with putting acpi_rsdp_addr at offset 0x0cc (_pad4)? > > >Juergen I'd prefer if you used __pad3 offset 0x70 to keep the large block, and that way your field is also aligned. However, if you have some specific reason to prefer __pad4 it's no big deal, although I'm curious what it would be. -- Sent from my Android device with K-9 Mail. Please excuse my brevity.