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=-9.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 59CD7C433DB for ; Wed, 13 Jan 2021 03:57:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 167B82312E for ; Wed, 13 Jan 2021 03:57:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725917AbhAMD5e (ORCPT ); Tue, 12 Jan 2021 22:57:34 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42510 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725818AbhAMD5e (ORCPT ); Tue, 12 Jan 2021 22:57:34 -0500 Received: from mail-pg1-x533.google.com (mail-pg1-x533.google.com [IPv6:2607:f8b0:4864:20::533]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 504AEC061786; Tue, 12 Jan 2021 19:56:54 -0800 (PST) Received: by mail-pg1-x533.google.com with SMTP id z21so645894pgj.4; Tue, 12 Jan 2021 19:56:54 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=tVybN2uO9LxG9ltd3tCKTHJYv7lU36O5UathtbI9Q9Q=; b=jLig4OWz6r5npRBnWnkYmtzqG5FaXvnjSp/GwVihv4kwV2tapBGwAF3xjarDP4svmh mmN3Em4/UnH964tt6spkMXBvTXAa1Xjxi6HY2VwIUlElZ/L/49drfsdWJz7rkYT/pJvu yntpxB6D25C4BgTjLzt3HccAWYqhBQRzY5xmbmcHg9uBakUAJ4cTw8WcABTwfYSf2utS bVK9ADZgPBqt1M4K8HOhkKFeNAlDtYVBHRWT6ioSEXPxxCLeolZujd32j7r9fme4RUHN 48XR8U765COw3RQNjeJq5sRrwMZ2sbfbQ/6nLd1YYq7tC2A1pN/yQ3g/lIYtxVpVamT0 EzIQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=tVybN2uO9LxG9ltd3tCKTHJYv7lU36O5UathtbI9Q9Q=; b=t3CEiCgqNcp1373FBCP8xvooFBqHbtMCx875YAIwZelMTsJYBXU8xuEa92Y+k6R44E amMUBh6GViP0A1CtFBIjXQoqmdkxtrPL7nEVBuFY71FE/EfZAnl+hi23gTbRm2JejlUQ GOk0EE9rW0PiHUJfaLXA8oO24Gu9AEkQBHKose4PKUCNag2A4EnBfk84XwdzjwGxzbjm PXE4lc6+NYXvOpmr2jMa6vbpmcW4V5ZuUohzFlwvLWxzx8qQBR9ReJjgVvniKoTe02zz AN3PYlsWf791TNz43WHWSLmgRgI5phxtljW2bczZE30ki1M+aZxQTvrgfbqCnfoKMm5H pHtA== X-Gm-Message-State: AOAM531TY4l4R9PpbP/Z4owNxKjwsbN9iADctnMPYk9w/rAk+AGdS4jo KT5lSm8f8deoVP9rqkY+nJo= X-Google-Smtp-Source: ABdhPJyNiwxgLNGhX03OzTQQ31jD0Jl7mxbRLHzGfQFw82uojIWRVt9otXa8r8jCLr9MzK1TtdQTHQ== X-Received: by 2002:a62:65c1:0:b029:1aa:ba52:fdfd with SMTP id z184-20020a6265c10000b02901aaba52fdfdmr143707pfb.7.1610510213683; Tue, 12 Jan 2021 19:56:53 -0800 (PST) Received: from [10.230.29.29] ([192.19.223.252]) by smtp.gmail.com with ESMTPSA id b4sm605572pju.33.2021.01.12.19.56.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 12 Jan 2021 19:56:52 -0800 (PST) Subject: Re: [RFC PATCH v3 0/6] Restricted DMA To: Tomasz Figa Cc: Claire Chang , Rob Herring , mpe@ellerman.id.au, benh@kernel.crashing.org, paulus@samba.org, "list@263.net:IOMMU DRIVERS" , Joerg Roedel , Will Deacon , Frank Rowand , Konrad Rzeszutek Wilk , boris.ostrovsky@oracle.com, jgross@suse.com, sstabellini@kernel.org, Christoph Hellwig , Marek Szyprowski , Robin Murphy , grant.likely@arm.com, xypron.glpk@gmx.de, Thierry Reding , mingo@kernel.org, bauerman@linux.ibm.com, peterz@infradead.org, Greg KH , Saravana Kannan , "Rafael J . Wysocki" , heikki.krogerus@linux.intel.com, Andy Shevchenko , Randy Dunlap , Dan Williams , Bartosz Golaszewski , linux-devicetree , lkml , linuxppc-dev@lists.ozlabs.org, xen-devel@lists.xenproject.org, Nicolas Boichat , Jim Quinlan References: <20210106034124.30560-1-tientzu@chromium.org> <78871151-947d-b085-db03-0d0bd0b55632@gmail.com> <23a09b9a-70fc-a7a8-f3ea-b0bfa60507f0@gmail.com> From: Florian Fainelli Message-ID: Date: Tue, 12 Jan 2021 19:56:49 -0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Firefox/78.0 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On 1/12/2021 6:29 PM, Tomasz Figa wrote: > Hi Florian, > > On Wed, Jan 13, 2021 at 3:01 AM Florian Fainelli wrote: >> >> On 1/11/21 11:48 PM, Claire Chang wrote: >>> On Fri, Jan 8, 2021 at 1:59 AM Florian Fainelli wrote: >>>> >>>> On 1/7/21 9:42 AM, Claire Chang wrote: >>>> >>>>>> Can you explain how ATF gets involved and to what extent it does help, >>>>>> besides enforcing a secure region from the ARM CPU's perpsective? Does >>>>>> the PCIe root complex not have an IOMMU but can somehow be denied access >>>>>> to a region that is marked NS=0 in the ARM CPU's MMU? If so, that is >>>>>> still some sort of basic protection that the HW enforces, right? >>>>> >>>>> We need the ATF support for memory MPU (memory protection unit). >>>>> Restricted DMA (with reserved-memory in dts) makes sure the predefined memory >>>>> region is for PCIe DMA only, but we still need MPU to locks down PCIe access to >>>>> that specific regions. >>>> >>>> OK so you do have a protection unit of some sort to enforce which region >>>> in DRAM the PCIE bridge is allowed to access, that makes sense, >>>> otherwise the restricted DMA region would only be a hint but nothing you >>>> can really enforce. This is almost entirely analogous to our systems then. >>> >>> Here is the example of setting the MPU: >>> https://github.com/ARM-software/arm-trusted-firmware/blob/master/plat/mediatek/mt8183/drivers/emi_mpu/emi_mpu.c#L132 >>> >>>> >>>> There may be some value in standardizing on an ARM SMCCC call then since >>>> you already support two different SoC vendors. >>>> >>>>> >>>>>> >>>>>> On Broadcom STB SoCs we have had something similar for a while however >>>>>> and while we don't have an IOMMU for the PCIe bridge, we do have a a >>>>>> basic protection mechanism whereby we can configure a region in DRAM to >>>>>> be PCIe read/write and CPU read/write which then gets used as the PCIe >>>>>> inbound region for the PCIe EP. By default the PCIe bridge is not >>>>>> allowed access to DRAM so we must call into a security agent to allow >>>>>> the PCIe bridge to access the designated DRAM region. >>>>>> >>>>>> We have done this using a private CMA area region assigned via Device >>>>>> Tree, assigned with a and requiring the PCIe EP driver to use >>>>>> dma_alloc_from_contiguous() in order to allocate from this device >>>>>> private CMA area. The only drawback with that approach is that it >>>>>> requires knowing how much memory you need up front for buffers and DMA >>>>>> descriptors that the PCIe EP will need to process. The problem is that >>>>>> it requires driver modifications and that does not scale over the number >>>>>> of PCIe EP drivers, some we absolutely do not control, but there is no >>>>>> need to bounce buffer. Your approach scales better across PCIe EP >>>>>> drivers however it does require bounce buffering which could be a >>>>>> performance hit. >>>>> >>>>> Only the streaming DMA (map/unmap) needs bounce buffering. >>>> >>>> True, and typically only on transmit since you don't really control >>>> where the sk_buff are allocated from, right? On RX since you need to >>>> hand buffer addresses to the WLAN chip prior to DMA, you can allocate >>>> them from a pool that already falls within the restricted DMA region, right? >>>> >>> >>> Right, but applying bounce buffering to RX will make it more secure. >>> The device won't be able to modify the content after unmap. Just like what >>> iommu_unmap does. >> >> Sure, however the goals of using bounce buffering equally applies to RX >> and TX in that this is the only layer sitting between a stack (block, >> networking, USB, etc.) and the underlying device driver that scales well >> in order to massage a dma_addr_t to be within a particular physical range. >> >> There is however room for improvement if the drivers are willing to >> change their buffer allocation strategy. When you receive Wi-Fi frames >> you need to allocate buffers for the Wi-Fi device to DMA into, and that >> happens ahead of the DMA transfers by the Wi-Fi device. At buffer >> allocation time you could very well allocate these frames from the >> restricted DMA region without having to bounce buffer them since the >> host CPU is in control over where and when to DMA into. >> > > That is, however, still a trade-off between saving that one copy and > protection from the DMA tampering with the packet contents when the > kernel is reading them. Notice how the copy effectively makes a > snapshot of the contents, guaranteeing that the kernel has a > consistent view of the packet, which is not true if the DMA could > modify the buffer contents in the middle of CPU accesses. I would say that the window just became so much narrower for the PCIe end-point to overwrite contents with the copy because it would have to happen within the dma_unmap_{page,single} time and before the copy is finished to the bounce buffer. -- Florian