[PATCH v4 2/5] vfio/pci: Add device denylist

[Giovanni Cabiddu <giovanni.cabiddu@xxxxxxxxx>]

Add denylist of devices that by default are not probed by vfio-pci.
Devices in this list may be susceptible to untrusted application, even
if the IOMMU is enabled. To be accessed via vfio-pci, the user has to
explicitly disable the denylist.

The denylist can be disabled via the module parameter disable_denylist.

Signed-off-by: Giovanni Cabiddu <giovanni.cabiddu@xxxxxxxxx>
---
 drivers/vfio/pci/vfio_pci.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 7c0779018b1b..0101f41e7834 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -60,6 +60,10 @@ module_param(enable_sriov, bool, 0644);
 MODULE_PARM_DESC(enable_sriov, "Enable support for SR-IOV configuration.  Enabling SR-IOV on a PF typically requires support of the userspace PF driver, enabling VFs without such support may result in non-functional VFs or PF.");
 #endif
 
+static bool disable_denylist;
+module_param(disable_denylist, bool, 0444);
+MODULE_PARM_DESC(disable_denylist, "Disable use of device denylist. Disabling the denylist allows binding to devices with known errata that may lead to exploitable stability or security issues when accessed by untrusted users.");
+
 static inline bool vfio_vga_disabled(void)
 {
 #ifdef CONFIG_VFIO_PCI_VGA
@@ -69,6 +73,29 @@ static inline bool vfio_vga_disabled(void)
 #endif
 }
 
+static bool vfio_pci_dev_in_denylist(struct pci_dev *pdev)
+{
+	return false;
+}
+
+static bool vfio_pci_is_denylisted(struct pci_dev *pdev)
+{
+	if (!vfio_pci_dev_in_denylist(pdev))
+		return false;
+
+	if (disable_denylist) {
+		pci_warn(pdev,
+			 "device denylist disabled - allowing device %04x:%04x.\n",
+			 pdev->vendor, pdev->device);
+		return false;
+	}
+
+	pci_warn(pdev, "%04x:%04x exists in vfio-pci device denylist, driver probing disallowed.\n",
+		 pdev->vendor, pdev->device);
+
+	return true;
+}
+
 /*
  * Our VGA arbiter participation is limited since we don't know anything
  * about the device itself.  However, if the device is the only VGA device
@@ -1847,6 +1874,9 @@ static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	struct iommu_group *group;
 	int ret;
 
+	if (vfio_pci_is_denylisted(pdev))
+		return -EINVAL;
+
 	if (pdev->hdr_type != PCI_HEADER_TYPE_NORMAL)
 		return -EINVAL;
 
@@ -2336,6 +2366,9 @@ static int __init vfio_pci_init(void)
 
 	vfio_pci_fill_ids();
 
+	if (disable_denylist)
+		pr_warn("device denylist disabled.\n");
+
 	return 0;
 
 out_driver:
-- 
2.26.2