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=-2.7 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 4AD07C04AA5 for ; Mon, 15 Oct 2018 13:44:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F237720842 for ; Mon, 15 Oct 2018 13:44:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="uwZjxeq+" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F237720842 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-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726605AbeJOV33 (ORCPT ); Mon, 15 Oct 2018 17:29:29 -0400 Received: from mail.kernel.org ([198.145.29.99]:49724 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726422AbeJOV33 (ORCPT ); Mon, 15 Oct 2018 17:29:29 -0400 Received: from localhost (173-25-171-118.client.mchsi.com [173.25.171.118]) (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 4BFF620644; Mon, 15 Oct 2018 13:44:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1539611046; bh=j72JDwspvCT720xgfxzSRFTHkvQpa8+mtonWbWz1Ay4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=uwZjxeq+0KXzEkkjcaJ4pDpKJvxekZDX5rt3sUwwQHeiagLgzNdnl3af/JR79CT83 0+HY7HElVuSPvWeDUPYi1JChjTy14Z42lv55cmJbC14CCiKasjC809dUM0eMWpMnXw nIGUXs+vc9+O9ZArhYwGdBwRh6pNgVzchG4IFXj8= Date: Mon, 15 Oct 2018 08:44:04 -0500 From: Bjorn Helgaas To: Dave Young Cc: bp@suse.de, thomas.lendacky@amd.com, brijesh.singh@amd.com, Lianbo Jiang , bhe@redhat.com, tiwai@suse.de, x86@kernel.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, mingo@redhat.com, baiyaowei@cmss.chinamobile.com, hpa@zytor.com, dan.j.williams@intel.com, tglx@linutronix.de, Vivek Goyal Subject: Re: [PATCH 1/3] x86/kexec: Correct KEXEC_BACKUP_SRC_END off-by-one error Message-ID: <20181015134404.GA5906@bhelgaas-glaptop.roam.corp.google.com> References: <153805773703.1157.14773321497580233478.stgit@bhelgaas-glaptop.roam.corp.google.com> <153805811578.1157.6948388946904655969.stgit@bhelgaas-glaptop.roam.corp.google.com> <20180930092110.GB6950@dhcp-128-65.nay.redhat.com> <20180930092741.GC6950@dhcp-128-65.nay.redhat.com> <20181015045138.GA9719@dhcp-128-65.nay.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181015045138.GA9719@dhcp-128-65.nay.redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 15, 2018 at 12:51:38PM +0800, Dave Young wrote: > On 09/30/18 at 05:27pm, Dave Young wrote: > > On 09/30/18 at 05:21pm, Dave Young wrote: > > > On 09/27/18 at 09:21am, Bjorn Helgaas wrote: > > > > From: Bjorn Helgaas > > > > > > > > The only use of KEXEC_BACKUP_SRC_END is as an argument to > > > > walk_system_ram_res(): > > > > > > > > int crash_load_segments(struct kimage *image) > > > > { > > > > ... > > > > walk_system_ram_res(KEXEC_BACKUP_SRC_START, KEXEC_BACKUP_SRC_END, > > > > image, determine_backup_region); > > > > > > > > walk_system_ram_res() expects "start, end" arguments that are inclusive, > > > > i.e., the range to be walked includes both the start and end addresses. > > > > > > Looking at the function comment of find_next_iomem_res, the res->end > > > should be exclusive, am I missing something? > > > > Oops, you fix it in 2nd patch, I apparently miss that. > > > > Since the fix of checking the end is in another patch, probably merge > > these two patches so that they are in one patch to avoid break bisect. > > Not sure if above comment was missed, Boris, would you mind to fold the > patch 1 and 2? Sorry, I did miss this comment. Patch 2 was for the very specific case of a single-byte resource at the end address, which we probably never see in practice. For patch 1, the find_next_iomem_res() function comment had "[res->start.res->end)", but I think the code actually treated it as "[res->start.res->end]", so the comment was inaccurate. Before my patches we had: #define KEXEC_BACKUP_SRC_START (0UL) #define KEXEC_BACKUP_SRC_END (640 * 1024UL) # 0xa0000 The intention is to search for system RAM resources that intersect this region: [mem 0x0-0x9ffff] The call is: walk_system_ram_res(KEXEC_BACKUP_SRC_START, KEXEC_BACKUP_SRC_END, ..., determine_backup_region); walk_system_ram_res(0, 0xa0000, ..., determine_backup_region); Assume iomem_resource contains this system RAM resource: [mem 0x90000-0xaffff] In find_next_iomem_res(), the "res" input parameter is the region to search: res->start = 0; # KEXEC_BACKUP_SRC_START res->end = 0xa0000; # KEXEC_BACKUP_SRC_END In one of the loop iterations we find the [mem 0x90000-0xaffff] resource (p): p->start = 0x90000; p->end = 0xaffff; if (p->start > end) # 0x90000 > 0xa0000? false if (p->end >= start && p->start < end) # 0xaffff >= 0 ? true # 0x90000 < 0xa0000 ? true break; # so we'll return part of "p" if (res->start < p->start) # 0x0 < 0x90000 ? true res->start = 0x90000; # trim beginning to p->start if (res->end > p->end) # 0xa0000 > 0xaffff ? false So find_next_iomem_res() returns with this: res->start = 0x90000; # trimmed to p->start res->end = 0xa0000; # unchanged from input [mem 0x90000-0xa0000] # returned resource (res) and we call determine_backup_region(res), which sets: image->arch.backup_src_start = 0x90000; image->arch.backup_src_sz = resource_size(res) # 0xa0000 - 0x90000 + 1 # (0x10001) This is incorrect. What we wanted was the part of [mem 0x90000-0xaffff] that intersects the first 640K, i.e., [mem 0x90000-0x9ffff], but what we got was [mem 0x90000-0xa0000], which is one byte too long. The resource returned find_next_iomem_res() always ends at the "res->end" supplied as an input parameter *unless* the input res->end is strictly greater than the p->end, when it is truncated to p->end. Bottom line, I don't think patches 1 and 2 need to be folded together because they fix different problems. Bjorn