From patchwork Fri Mar 18 17:42:58 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Robin Murphy X-Patchwork-Id: 552980 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B16D7C433FE for ; Fri, 18 Mar 2022 17:43:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239714AbiCRRod (ORCPT ); Fri, 18 Mar 2022 13:44:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42098 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239736AbiCRRob (ORCPT ); Fri, 18 Mar 2022 13:44:31 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id E8376A76FF; Fri, 18 Mar 2022 10:43:11 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id AE1811515; Fri, 18 Mar 2022 10:43:11 -0700 (PDT) Received: from e121345-lin.cambridge.arm.com (e121345-lin.cambridge.arm.com [10.1.196.40]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 45A903F7B4; Fri, 18 Mar 2022 10:43:10 -0700 (PDT) From: Robin Murphy To: joro@8bytes.org, baolu.lu@linux.intel.com, andreas.noever@gmail.com, michael.jamet@intel.com, mika.westerberg@linux.intel.com, YehezkelShB@gmail.com Cc: iommu@lists.linux-foundation.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, mario.limonciello@amd.com, hch@lst.de Subject: [PATCH v2 2/2] thunderbolt: Make iommu_dma_protection more accurate Date: Fri, 18 Mar 2022 17:42:58 +0000 Message-Id: <0dd14883930c9f55ace22162e23765a37d91a057.1647624084.git.robin.murphy@arm.com> X-Mailer: git-send-email 2.28.0.dirty In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org Between me trying to get rid of iommu_present() and Mario wanting to support the AMD equivalent of DMAR_PLATFORM_OPT_IN, scrutiny has shown that the iommu_dma_protection attribute is being far too optimistic. Even if an IOMMU might be present for some PCI segment in the system, that doesn't necessarily mean it provides translation for the device(s) we care about. Furthermore, all that DMAR_PLATFORM_OPT_IN really does is tell us that memory was protected before the kernel was loaded, and prevent the user from disabling the intel-iommu driver entirely. While that lets us assume kernel integrity, what matters for actual runtime DMA protection is whether we trust individual devices, based on the "external facing" property that we expect firmware to describe for Thunderbolt ports. It's proven challenging to determine the appropriate ports accurately given the variety of possible topologies, so while still not getting a perfect answer, by putting enough faith in firmware we can at least get a good bit closer. If we can see that any device near a Thunderbolt NHI has all the requisites for Kernel DMA Protection, chances are that it *is* a relevant port, but moreover that implies that firmware is playing the game overall, so we'll use that to assume that all Thunderbolt ports should be correctly marked and thus will end up fully protected. CC: Mario Limonciello Signed-off-by: Robin Murphy Acked-by: Christoph Hellwig --- v2: Give up trying to look for specific devices, just look for evidence that firmware cares at all. drivers/thunderbolt/domain.c | 12 +++-------- drivers/thunderbolt/nhi.c | 41 ++++++++++++++++++++++++++++++++++++ include/linux/thunderbolt.h | 2 ++ 3 files changed, 46 insertions(+), 9 deletions(-) diff --git a/drivers/thunderbolt/domain.c b/drivers/thunderbolt/domain.c index 7018d959f775..2889a214dadc 100644 --- a/drivers/thunderbolt/domain.c +++ b/drivers/thunderbolt/domain.c @@ -7,9 +7,7 @@ */ #include -#include #include -#include #include #include #include @@ -257,13 +255,9 @@ static ssize_t iommu_dma_protection_show(struct device *dev, struct device_attribute *attr, char *buf) { - /* - * Kernel DMA protection is a feature where Thunderbolt security is - * handled natively using IOMMU. It is enabled when IOMMU is - * enabled and ACPI DMAR table has DMAR_PLATFORM_OPT_IN set. - */ - return sprintf(buf, "%d\n", - iommu_present(&pci_bus_type) && dmar_platform_optin()); + struct tb *tb = container_of(dev, struct tb, dev); + + return sysfs_emit(buf, "%d\n", tb->nhi->iommu_dma_protection); } static DEVICE_ATTR_RO(iommu_dma_protection); diff --git a/drivers/thunderbolt/nhi.c b/drivers/thunderbolt/nhi.c index c73da0532be4..9e396e283792 100644 --- a/drivers/thunderbolt/nhi.c +++ b/drivers/thunderbolt/nhi.c @@ -14,6 +14,7 @@ #include #include #include +#include #include #include #include @@ -1102,6 +1103,45 @@ static void nhi_check_quirks(struct tb_nhi *nhi) nhi->quirks |= QUIRK_AUTO_CLEAR_INT; } +static int nhi_check_iommu_pdev(struct pci_dev *pdev, void *data) +{ + if (!pdev->untrusted || + !dev_iommu_capable(&pdev->dev, IOMMU_CAP_PRE_BOOT_PROTECTION)) + return 0; + *(bool *)data = true; + return 1; /* Stop walking */ +} + +static void nhi_check_iommu(struct tb_nhi *nhi) +{ + struct pci_bus *bus = nhi->pdev->bus; + bool port_ok = false; + + /* + * Ideally what we'd do here is grab every PCI device that + * represents a tunnelling adapter for this NHI and check their + * status directly, but unfortunately USB4 seems to make it + * obnoxiously difficult to reliably make any correlation. + * + * So for now we'll have to bodge it... Hoping that the system + * is at least sane enough that an adapter is in the same PCI + * segment as its NHI, if we can find *something* on that segment + * which meets the requirements for Kernel DMA Protection, we'll + * take that to imply that firmware is aware and has (hopefully) + * done the right thing in general. We need to know that the PCI + * layer has seen the ExternalFacingPort property and propagated + * it to the "untrusted" flag that the IOMMU layer will then + * enforce, but also that the IOMMU driver itself can be trusted + * not to have been subverted by a pre-boot DMA attack. + */ + while (bus->parent) + bus = bus->parent; + + pci_walk_bus(bus, nhi_check_iommu_pdev, &port_ok); + + nhi->iommu_dma_protection = port_ok; +} + static int nhi_init_msi(struct tb_nhi *nhi) { struct pci_dev *pdev = nhi->pdev; @@ -1219,6 +1259,7 @@ static int nhi_probe(struct pci_dev *pdev, const struct pci_device_id *id) return -ENOMEM; nhi_check_quirks(nhi); + nhi_check_iommu(nhi); res = nhi_init_msi(nhi); if (res) { diff --git a/include/linux/thunderbolt.h b/include/linux/thunderbolt.h index 124e13cb1469..7a8ad984e651 100644 --- a/include/linux/thunderbolt.h +++ b/include/linux/thunderbolt.h @@ -465,6 +465,7 @@ static inline struct tb_xdomain *tb_service_parent(struct tb_service *svc) * @msix_ida: Used to allocate MSI-X vectors for rings * @going_away: The host controller device is about to disappear so when * this flag is set, avoid touching the hardware anymore. + * @iommu_dma_protection: An IOMMU will isolate external-facing ports. * @interrupt_work: Work scheduled to handle ring interrupt when no * MSI-X is used. * @hop_count: Number of rings (end point hops) supported by NHI. @@ -479,6 +480,7 @@ struct tb_nhi { struct tb_ring **rx_rings; struct ida msix_ida; bool going_away; + bool iommu_dma_protection; struct work_struct interrupt_work; u32 hop_count; unsigned long quirks;