[RFC/RFT] Add noats flag to boot parameters

[Gil Kupfer <gilkup@gmail.com>]

This patch adds noats option to the pci boot parameter.
When noats is selected, all ATS related functions fail immediately and
the IOMMU is configured to not use device-iotlb.

Any function that checks for ATS capabilities directly against the
devices should also check this flag. (Currently, such functions exist
only in IOMMU drivers, and they are covered by this patch.)

The motivation behind this patch is the existence of malicious devices.
Lots of research has been done about how to utilitize the IOMMU as a
protection from such devices. When ATS is supported, any I/O device can
access any physical access by faking device-IOTLB entries.
Adding the ability to ignore these entries lets sysadmins enhance system
security.

Signed-off-by: Gil Kupfer <gilkup@cs.technion.ac.il>

---
This patch is intended to add the ability to disable ATS at boot time.

My IOMMU has the ATS ecap but I don't have any PCI device that supports
ATS so I can't fully test it. However, I did ran it (with and without the
new boot flag) on QEMU with virtualized IOMMU with the device-iotlb flag
and it seems that at least the machine does not crush.

QEMU version:
	master branch from Jul 11 2017
	commit aa916e409c04 ("Merge 29741be b876804")
---
 Documentation/admin-guide/kernel-parameters.txt |  2 ++
 drivers/iommu/amd_iommu.c                       | 11 ++++++++---
 drivers/iommu/intel-iommu.c                     |  3 ++-
 drivers/pci/ats.c                               |  3 +++
 drivers/pci/pci.c                               |  7 +++++++
 include/linux/pci.h                             |  2 ++
 6 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 7737ab5..f443362 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3000,6 +3000,8 @@
 		pcie_scan_all	Scan all possible PCIe devices.  Otherwise we
 				only look for one device below a PCIe downstream
 				port.
+		noats		[PCIE, Intel-IOMMU, AMD-IOMMU]
+				do not use PCIe ATS (and IOMMU device-iotlb).
 
 	pcie_aspm=	[PCIE] Forcibly enable or disable PCIe Active State Power
 			Management.
diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index 0f1219f..2aa757e 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -388,6 +388,9 @@ static bool pci_iommuv2_capable(struct pci_dev *pdev)
 	};
 	int i, pos;
 
+	if (is_pcie_ats_disabled())
+		return false;
+
 	for (i = 0; i < 3; ++i) {
 		pos = pci_find_ext_capability(pdev, caps[i]);
 		if (pos == 0)
@@ -3602,9 +3605,11 @@ int amd_iommu_device_info(struct pci_dev *pdev,
 
 	memset(info, 0, sizeof(*info));
 
-	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_ATS);
-	if (pos)
-		info->flags |= AMD_IOMMU_DEVICE_FLAG_ATS_SUP;
+	if (!is_pcie_ats_disabled()) {
+		pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_ATS);
+		if (pos)
+			info->flags |= AMD_IOMMU_DEVICE_FLAG_ATS_SUP;
+	}
 
 	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI);
 	if (pos)
diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index fc2765c..7ac4adc 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -2434,7 +2434,8 @@ static struct dmar_domain *dmar_insert_one_dev_info(struct intel_iommu *iommu,
 	if (dev && dev_is_pci(dev)) {
 		struct pci_dev *pdev = to_pci_dev(info->dev);
 
-		if (ecap_dev_iotlb_support(iommu->ecap) &&
+		if (!is_pcie_ats_disabled() &&
+		    ecap_dev_iotlb_support(iommu->ecap) &&
 		    pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_ATS) &&
 		    dmar_find_matched_atsr_unit(pdev))
 			info->ats_supported = 1;
diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
index eeb9fb2..619024d 100644
--- a/drivers/pci/ats.c
+++ b/drivers/pci/ats.c
@@ -21,6 +21,9 @@ void pci_ats_init(struct pci_dev *dev)
 {
 	int pos;
 
+	if (is_pcie_ats_disabled())
+		return;
+
 	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ATS);
 	if (!pos)
 		return;
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 563901c..eb77590 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -109,6 +109,10 @@ unsigned int pcibios_max_latency = 255;
 /* If set, the PCIe ARI capability will not be used. */
 static bool pcie_ari_disabled;
 
+/* If set, the PCIe ATS capability will not be used. */
+static bool pcie_ats_disabled;
+bool is_pcie_ats_disabled(void) { return pcie_ats_disabled; }
+
 /* Disable bridge_d3 for all PCIe ports */
 static bool pci_bridge_d3_disable;
 /* Force bridge_d3 for all PCIe ports */
@@ -5430,6 +5434,9 @@ static int __init pci_setup(char *str)
 		if (*str && (str = pcibios_setup(str)) && *str) {
 			if (!strcmp(str, "nomsi")) {
 				pci_no_msi();
+			} else if (!strncmp(str, "noats", 5)) {
+				pr_info("PCIe: ATS is disabled\n");
+				pcie_ats_disabled = true;
 			} else if (!strcmp(str, "noaer")) {
 				pci_no_aer();
 			} else if (!strncmp(str, "realloc=", 8)) {
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 8039f9f..58fe5fb 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1420,6 +1420,8 @@ int  ht_create_irq(struct pci_dev *dev, int idx);
 void ht_destroy_irq(unsigned int irq);
 #endif /* CONFIG_HT_IRQ */
 
+bool is_pcie_ats_disabled(void);
+
 #ifdef CONFIG_PCI_ATS
 /* Address Translation Service */
 void pci_ats_init(struct pci_dev *dev);
-- 
2.7.4