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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED autolearn=unavailable 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 C1CDCC43381 for ; Sat, 2 Mar 2019 06:13:14 +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 8F81F206DD for ; Sat, 2 Mar 2019 06:13:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="HSbwXZxH" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8F81F206DD Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=huawei.com 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:Date: Message-ID:From:References:To:Subject:Reply-To:Content-ID:Content-Description :Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=6oqGcHXPFQK0UXKNrWSDw3DLB/bhbbBW1jMSi5KQkbs=; b=HSbwXZxHKymBYK RF0q3clhB1gnUOadlwApx/zPznJ/0a7up3AVkPOnVnSfmR4WtOs4CSE235yfw0VVuVqwlKGmPj4oR TA7euoHkUY38p2jz4EgRTyk9VvfPYDbBEkWHo3E3BQPieOLffMrUuZAU2lMZpxnQSPwtcecf6rLDK lrUE1e2nwQacWvbp7lxmvTLPF8c5kQngo+KxVgY3m1NJidzxW4zqjTBF+2ZLvlnxtfhfLoWIAe6r8 av/b+hCRasHH+RjoAMQJSomh13fphpcp4bSgB+oX3BQQcs715qAMzLoeWj/4jmmG1km5dpPMIWdxr lOukpJbgjsUm8ts7FJzQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gzxtY-0004CN-4n; Sat, 02 Mar 2019 06:13:12 +0000 Received: from szxga06-in.huawei.com ([45.249.212.32] helo=huawei.com) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1gzxtU-0004Bh-3L for linux-arm-kernel@lists.infradead.org; Sat, 02 Mar 2019 06:13:10 +0000 Received: from DGGEMS409-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id C2181738D0A63C084325; Sat, 2 Mar 2019 14:12:58 +0800 (CST) Received: from [127.0.0.1] (10.177.23.164) by DGGEMS409-HUB.china.huawei.com (10.3.19.209) with Microsoft SMTP Server id 14.3.408.0; Sat, 2 Mar 2019 14:12:50 +0800 Subject: Re: [PATCH RFC 1/1] iommu: set the default iommu-dma mode as non-strict To: Jean-Philippe Brucker , Hanjun Guo , John Garry , Robin Murphy , Will Deacon , Joerg Roedel , linux-arm-kernel , iommu , linux-kernel References: <20190131135211.6732-1-thunder.leizhen@huawei.com> <94b9b0c9-1a24-63ba-5abe-5f6d79fed415@arm.com> <5C78B89C.7040100@huawei.com> From: "Leizhen (ThunderTown)" Message-ID: <5C7A1EE1.6020200@huawei.com> Date: Sat, 2 Mar 2019 14:12:49 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: X-Originating-IP: [10.177.23.164] X-CFilter-Loop: Reflected X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190301_221308_310675_36F00E48 X-CRM114-Status: GOOD ( 20.27 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Yunsheng Lin , Linuxarm 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 2019/3/1 19:07, Jean-Philippe Brucker wrote: > 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 It seems impossible to have such driver. The modules insmod by root users should be guaranteed by themselves. > (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... Yes, so that we have no need to consider untrusted drivers. > > 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. I plan to add an attribute file for each device, espcially for hotplug devices. And let the root users to decide which mode should be used, strict or non-strict. Becasue they should known whether the hot-plug divice is trusted or not. > > 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 >>> >>> >>> . >>> >> > > > . > -- Thanks! BestRegards _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel