From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754137AbbIWSWK (ORCPT ); Wed, 23 Sep 2015 14:22:10 -0400 Received: from mail-by2on0096.outbound.protection.outlook.com ([207.46.100.96]:9174 "EHLO na01-by2-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752802AbbIWSWH (ORCPT ); Wed, 23 Sep 2015 14:22:07 -0400 Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=David.Daney@caviumnetworks.com; Message-ID: <5602EDC4.3040603@caviumnetworks.com> Date: Wed, 23 Sep 2015 11:21:56 -0700 From: David Daney User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 MIME-Version: 1.0 To: Will Deacon CC: David Daney , "linux-kernel@vger.kernel.org" , Bjorn Helgaas , "linux-pci@vger.kernel.org" , Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , "Kumar Gala" , "linux-arm-kernel@lists.infradead.org" , "devicetree@vger.kernel.org" , Marc Zyngier , "David Daney" Subject: Re: [PATCH v2 4/5] PCI: generic: Correct, and avoid overflow, in bus_max calculation. References: <1442527332-1174-1-git-send-email-ddaney.cavm@gmail.com> <1442527332-1174-5-git-send-email-ddaney.cavm@gmail.com> <20150923180157.GV7356@arm.com> In-Reply-To: <20150923180157.GV7356@arm.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [64.2.3.194] X-ClientProxiedBy: DM2PR07CA0011.namprd07.prod.outlook.com (10.141.52.139) To BY1PR0701MB1724.namprd07.prod.outlook.com (25.162.111.143) X-Microsoft-Exchange-Diagnostics: 1;BY1PR0701MB1724;2:Oi/obz7YpUzAvjerK96iNsS9JFcKE8egvqBb6Nz29laNhkOvT9d527gJV9aRLYeHZKVsNY6AVAtiqYwTLjYiuqcFRr2ApmMRjz4ax7w3IqASfaxC+erw+I8uMPzZ8pJXNnZHGiBu6UjmhW7RxSh15Xf6fsl5EnyPWn3Yd5nrr+I=;3:zYEE8uAARebMRW+RcMbtGbO5gaxGRpbA0LcNdm8W/Wf2n6ecurhhZ3WXC5bbpZVfhp4+BEv+Ny/waVcU2OWVjHwC4+Nv2Tc06ZBMXL6DWwdj6WdieoQV8c0+Iz6PEsxPLSmd3YnKBxzy5ddDbHHU6w==;25:ZQC+oW2v9Wa8niIlIcB2tMqP0BrPbkLVmQHTlwNQhKogYO4duyEXdJaxQzh2A7QIqU1N08m36D0WyvLtknNJXOY9pi+1+nPIiLbghYEMzXZg481b8D58LBfeZlYYta1z4Ic14BIL7sdC/m2maGq9ci7/4W6eawuLtu5uvOZj3T/oI0citcUioa/NodE3lS0SKCwcY6bgVvnvE12s3iJjXd4YcBDcyYATufgLiH8c5/cFiGFDTuhmI/1WjOsreSgIR8gRMDLJJrHjSlyiAznUAQ== X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:;SRVR:BY1PR0701MB1724; 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>> - u8 bus_max; >> + int bus_max; >> resource_size_t busn; >> struct resource *bus_range; >> struct device *dev = pci->host.dev.parent; >> @@ -177,8 +177,9 @@ static int gen_pci_parse_map_cfg_windows(struct gen_pci *pci) >> } >> >> /* Limit the bus-range to fit within reg */ >> - bus_max = pci->cfg.bus_range->start + >> - (resource_size(&pci->cfg.res) >> pci->cfg.ops.bus_shift) - 1; >> + bus_max = (resource_size(&pci->cfg.res) >> pci->cfg.ops.bus_shift) - 1; >> + if (bus_max > 255) >> + bus_max = 255; > > I still don't understand the need for this part. If the cfg space is bigger > than bus_max, isn't that simply an invalid resource? Given that the resource > could be broken in other ways too, this check feels more like a specific > workaround rather than generally useful code. Imagine... bus-range [0x80 .. 0xff], this requires a cfg.res that will cover the entire range of 0..0xff. according to the calculations above, (resource_size(&pci->cfg.res) >> pci->cfg.ops.bus_shift) - 1 will have a value of 0xff, so... bus_max = 0x80 + 0xff -> OVERFLOW of u8! That is not useful. bus_max should represent the largest bus number that can be covered by cfg.res. That is what my patch is attempting to accomplish. Calculate the largest bus number that can be accommodated by cfg.res, and then clamp it to 0xff. David Daney.