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 A83BCC43381 for ; Fri, 1 Mar 2019 11:07:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7730C20851 for ; Fri, 1 Mar 2019 11:07:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733008AbfCALHt (ORCPT ); Fri, 1 Mar 2019 06:07:49 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:33218 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727932AbfCALHt (ORCPT ); Fri, 1 Mar 2019 06:07:49 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id BA117EBD; Fri, 1 Mar 2019 03:07:48 -0800 (PST) Received: from [10.1.197.2] (ostrya.cambridge.arm.com [10.1.197.2]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A1AE83F575; Fri, 1 Mar 2019 03:07:46 -0800 (PST) Subject: Re: [PATCH RFC 1/1] iommu: set the default iommu-dma mode as non-strict To: "Leizhen (ThunderTown)" , Hanjun Guo , John Garry , Robin Murphy , Will Deacon , Joerg Roedel , linux-arm-kernel , iommu , linux-kernel Cc: Yunsheng Lin , Linuxarm References: <20190131135211.6732-1-thunder.leizhen@huawei.com> <94b9b0c9-1a24-63ba-5abe-5f6d79fed415@arm.com> <5C78B89C.7040100@huawei.com> From: Jean-Philippe Brucker Message-ID: Date: Fri, 1 Mar 2019 11:07:26 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <5C78B89C.7040100@huawei.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Leizhen, On 01/03/2019 04:44, Leizhen (ThunderTown) wrote: > > > On 2019/2/26 20:36, Hanjun Guo wrote: >> Hi Jean, >> >> On 2019/1/31 22:55, Jean-Philippe Brucker wrote: >>> Hi, >>> >>> On 31/01/2019 13:52, Zhen Lei wrote: >>>> Currently, many peripherals are faster than before. For example, the top >>>> speed of the older netcard is 10Gb/s, and now it's more than 25Gb/s. But >>>> when iommu page-table mapping enabled, it's hard to reach the top speed >>>> in strict mode, because of frequently map and unmap operations. In order >>>> to keep abreast of the times, I think it's better to set non-strict as >>>> default. >>> >>> Most users won't be aware of this relaxation and will have their system >>> vulnerable to e.g. thunderbolt hotplug. See for example 4.3 Deferred >>> Invalidation in >>> http://www.cs.technion.ac.il/users/wwwb/cgi-bin/tr-get.cgi/2018/MSC/MSC-2018-21.pdf > Hi Jean, > > In fact, we have discussed the vulnerable of deferred invalidation before upstream > the non-strict patches. The attacks maybe possible because of an untrusted device or > the mistake of the device driver. And we limited the VFIO to still use strict mode. > As mentioned in the pdf, limit the freed memory with deferred invalidation only to > be reused by the device, can mitigate the vulnerability. But it's too hard to implement > it now. > A compromise maybe we only apply non-strict to (1) dma_free_coherent, because the > memory is controlled by DMA common module, so we can make the memory to be freed after > the global invalidation in the timer handler. (2) And provide some new APIs related to > iommu_unmap_page/sg, these new APIs deferred invalidation. And the candiate device > drivers update the APIs if they want to improve performance. (3) Make sure that only > the trusted devices and trusted drivers can apply (1) and (2). For example, the driver > must be built into kernel Image. Do we have a notion of untrusted kernel drivers? A userspace driver (VFIO) is untrusted, ok. But a malicious driver loaded into the kernel address space would have much easier ways to corrupt the system than to exploit lazy mode... For (3), I agree that we should at least disallow lazy mode if pci_dev->untrusted is set. At the moment it means that we require the strictest IOMMU configuration for external-facing PCI ports, but it can be extended to blacklist other vulnerable devices or locations. If you do (3) then maybe we don't need (1) and (2), which require a tonne of work in the DMA and IOMMU layers (but would certainly be nice to see, since it would also help handle ATS invalidation timeouts) Thanks, Jean > So that some high-end trusted devices use non-strict mode, and keep others still using > strict mode. The drivers who want to use non-strict mode, should change to use new APIs > by themselves. > > >>> >>> Why not keep the policy to secure by default, as we do for >>> iommu.passthrough? And maybe add something similar to >>> CONFIG_IOMMU_DEFAULT_PASSTRHOUGH? It's easy enough for experts to pass a >>> command-line argument or change the default config. >> >> Sorry for the late reply, it was Chinese new year, and we had a long discussion >> internally, we are fine to add a Kconfig but not sure OS vendors will set it >> to default y. >> >> OS vendors seems not happy to pass a command-line argument, to be honest, >> this is our motivation to enable non-strict as default. Hope OS vendors >> can see this email thread, and give some input here. >> >> Thanks >> Hanjun >> >> >> . >> >