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Date:   Wed,  3 Jun 2020 06:03:17 -0700
Message-Id: <20200603130317.94672-1-rajatja@google.com>
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Subject: [PATCH v4] iommu/vt-d: Don't apply gfx quirks to untrusted devices
From:   Rajat Jain <rajatja@google.com>
To:     David Woodhouse <dwmw2@infradead.org>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        Joerg Roedel <joro@8bytes.org>,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
        Mika Westerberg <mika.westerberg@intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        lalithambika.krishnakumar@intel.com
Cc:     Rajat Jain <rajatja@google.com>, rajatxjain@gmail.com,
        pmalani@google.com, bleung@google.com, levinale@google.com,
        zsm@google.com, mnissler@google.com, tbroch@google.com
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Currently, an external malicious PCI device can masquerade the VID:PID
of faulty gfx devices, and thus apply iommu quirks to effectively
disable the IOMMU restrictions for itself.

Thus we need to ensure that the device we are applying quirks to, is
indeed an internal trusted device.

Signed-off-by: Rajat Jain <rajatja@google.com>
Acked-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Ashok Raj <ashok.raj@intel.com>
---
v4: - Add Ashok Raj's "Reviewed-by"
    - Use pci_info() and split debug print cleanly into 2 statements. 
v3: - Separate out the warning mesage in a function to be called from
      other places. Change the warning string as suggested.
v2: - Change the warning print strings.
    - Add Lu Baolu's acknowledgement.

 drivers/iommu/intel-iommu.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index ef0a5246700e5..efd1e5de947b9 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -6185,6 +6185,23 @@ intel_iommu_domain_set_attr(struct iommu_domain *domain,
 	return ret;
 }
 
+/*
+ * Check that the device does not live on an external facing PCI port that is
+ * marked as untrusted. Such devices should not be able to apply quirks and
+ * thus not be able to bypass the IOMMU restrictions.
+ */
+static bool risky_device(struct pci_dev *pdev)
+{
+	if (pdev->untrusted) {
+		pci_info(pdev,
+			 "Skipping IOMMU quirk for dev [%04X:%04X] on untrusted PCI link\n",
+			 pdev->vendor, pdev->device);
+		pci_info(pdev, "Please check with your BIOS/Platform vendor about this\n");
+		return true;
+	}
+	return false;
+}
+
 const struct iommu_ops intel_iommu_ops = {
 	.capable		= intel_iommu_capable,
 	.domain_alloc		= intel_iommu_domain_alloc,
@@ -6214,6 +6231,9 @@ const struct iommu_ops intel_iommu_ops = {
 
 static void quirk_iommu_igfx(struct pci_dev *dev)
 {
+	if (risky_device(dev))
+		return;
+
 	pci_info(dev, "Disabling IOMMU for graphics on this chipset\n");
 	dmar_map_gfx = 0;
 }
@@ -6255,6 +6275,9 @@ DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x163D, quirk_iommu_igfx);
 
 static void quirk_iommu_rwbf(struct pci_dev *dev)
 {
+	if (risky_device(dev))
+		return;
+
 	/*
 	 * Mobile 4 Series Chipset neglects to set RWBF capability,
 	 * but needs it. Same seems to hold for the desktop versions.
@@ -6285,6 +6308,9 @@ static void quirk_calpella_no_shadow_gtt(struct pci_dev *dev)
 {
 	unsigned short ggc;
 
+	if (risky_device(dev))
+		return;
+
 	if (pci_read_config_word(dev, GGC, &ggc))
 		return;
 
@@ -6318,6 +6344,12 @@ static void __init check_tylersburg_isoch(void)
 	pdev = pci_get_device(PCI_VENDOR_ID_INTEL, 0x3a3e, NULL);
 	if (!pdev)
 		return;
+
+	if (risky_device(pdev)) {
+		pci_dev_put(pdev);
+		return;
+	}
+
 	pci_dev_put(pdev);
 
 	/* System Management Registers. Might be hidden, in which case
@@ -6327,6 +6359,11 @@ static void __init check_tylersburg_isoch(void)
 	if (!pdev)
 		return;
 
+	if (risky_device(pdev)) {
+		pci_dev_put(pdev);
+		return;
+	}
+
 	if (pci_read_config_dword(pdev, 0x188, &vtisochctrl)) {
 		pci_dev_put(pdev);
 		return;
-- 
2.27.0.rc2.251.g90737beb825-goog