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0014-xen-pciback-add-attribute-to-allow-MSI-enable-flag-w.patch
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0014-xen-pciback-add-attribute-to-allow-MSI-enable-flag-w.patch
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From 6403b443fb441d4206d59b34395f0bd6e876f168 Mon Sep 17 00:00:00 2001
From: HW42 <hw42@ipsumj.de>
Date: Tue, 12 Sep 2017 00:49:02 +0200
Subject: [PATCH] xen-pciback: add attribute to allow MSI enable flag writes
QEMU running in a stubdom needs to be able to set the MSI enable flag in
the PCI config space. This adds an attribute 'allow_msi_enable' which
when set for a PCI device allows writes to this flag. The toolstack will
need to set this for stubdoms.
This should not introduce any new security issues since a malicious
guest (or stubdom) can already generate MSIs through other ways, see
[1] page 8.
[1]: https://invisiblethingslab.com/resources/2011/Software%20Attacks%20on%20Intel%20VT-d.pdf
---
.../xen/xen-pciback/conf_space_capability.c | 39 +++++++++++
drivers/xen/xen-pciback/pci_stub.c | 64 +++++++++++++++++++
drivers/xen/xen-pciback/pciback.h | 1 +
3 files changed, 104 insertions(+)
diff --git a/drivers/xen/xen-pciback/conf_space_capability.c b/drivers/xen/xen-pciback/conf_space_capability.c
index e5694133ebe5..4be817f448c3 100644
--- a/drivers/xen/xen-pciback/conf_space_capability.c
+++ b/drivers/xen/xen-pciback/conf_space_capability.c
@@ -189,6 +189,40 @@ static const struct config_field caplist_pm[] = {
{}
};
+#define MSI_OK_BITS (PCI_MSI_FLAGS_ENABLE)
+
+static int msi_flags_write(struct pci_dev *dev, int offset, u16 new_value,
+ void *data)
+{
+ int err;
+ u16 old_value;
+ struct xen_pcibk_dev_data *dev_data = pci_get_drvdata(dev);
+
+ if (xen_pcibk_permissive || dev_data->permissive)
+ goto write;
+
+ err = pci_read_config_word(dev, offset, &old_value);
+ if (err)
+ return err;
+
+ if (!dev_data->allow_msi_enable
+ || (new_value ^ old_value) & ~MSI_OK_BITS)
+ return PCIBIOS_SET_FAILED;
+
+write:
+ return pci_write_config_word(dev, offset, new_value);
+}
+
+static const struct config_field caplist_msi[] = {
+ {
+ .offset = PCI_MSI_FLAGS,
+ .size = 2,
+ .u.w.read = xen_pcibk_read_config_word,
+ .u.w.write = msi_flags_write,
+ },
+ {}
+};
+
static struct xen_pcibk_config_capability xen_pcibk_config_capability_pm = {
.capability = PCI_CAP_ID_PM,
.fields = caplist_pm,
@@ -197,11 +231,16 @@ static struct xen_pcibk_config_capability xen_pcibk_config_capability_vpd = {
.capability = PCI_CAP_ID_VPD,
.fields = caplist_vpd,
};
+static struct xen_pcibk_config_capability xen_pcibk_config_capability_msi = {
+ .capability = PCI_CAP_ID_MSI,
+ .fields = caplist_msi,
+};
int xen_pcibk_config_capability_init(void)
{
register_capability(&xen_pcibk_config_capability_vpd);
register_capability(&xen_pcibk_config_capability_pm);
+ register_capability(&xen_pcibk_config_capability_msi);
return 0;
}
diff --git a/drivers/xen/xen-pciback/pci_stub.c b/drivers/xen/xen-pciback/pci_stub.c
index 097410a7cdb7..fb6a4a43c11d 100644
--- a/drivers/xen/xen-pciback/pci_stub.c
+++ b/drivers/xen/xen-pciback/pci_stub.c
@@ -304,6 +304,8 @@ void pcistub_put_pci_dev(struct pci_dev *dev)
xen_pcibk_config_reset_dev(dev);
xen_pcibk_config_free_dyn_fields(dev);
+ dev_data->allow_msi_enable = 0;
+
xen_unregister_device_domain_owner(dev);
spin_lock_irqsave(&found_psdev->lock, flags);
@@ -1431,6 +1433,63 @@ static ssize_t permissive_show(struct device_driver *drv, char *buf)
}
static DRIVER_ATTR_RW(permissive);
+static ssize_t allow_msi_enable_store(struct device_driver *drv, const char *buf,
+ size_t count)
+{
+ int domain, bus, slot, func;
+ int err;
+ struct pcistub_device *psdev;
+ struct xen_pcibk_dev_data *dev_data;
+
+ err = str_to_slot(buf, &domain, &bus, &slot, &func);
+ if (err)
+ goto out;
+
+ psdev = pcistub_device_find(domain, bus, slot, func);
+ if (!psdev) {
+ err = -ENODEV;
+ goto out;
+ }
+
+ dev_data = pci_get_drvdata(psdev->dev);
+ /* the driver data for a device should never be null at this point */
+ if (!dev_data) {
+ err = -ENXIO;
+ goto release;
+ }
+ dev_data->allow_msi_enable = 1;
+release:
+ pcistub_device_put(psdev);
+out:
+ if (!err)
+ err = count;
+ return err;
+}
+
+static ssize_t allow_msi_enable_show(struct device_driver *drv, char *buf)
+{
+ struct pcistub_device *psdev;
+ struct xen_pcibk_dev_data *dev_data;
+ size_t count = 0;
+ unsigned long flags;
+ spin_lock_irqsave(&pcistub_devices_lock, flags);
+ list_for_each_entry(psdev, &pcistub_devices, dev_list) {
+ if (count >= PAGE_SIZE)
+ break;
+ if (!psdev->dev)
+ continue;
+ dev_data = pci_get_drvdata(psdev->dev);
+ if (!dev_data || !dev_data->allow_msi_enable)
+ continue;
+ count +=
+ scnprintf(buf + count, PAGE_SIZE - count, "%s\n",
+ pci_name(psdev->dev));
+ }
+ spin_unlock_irqrestore(&pcistub_devices_lock, flags);
+ return count;
+}
+static DRIVER_ATTR_RW(allow_msi_enable);
+
static void pcistub_exit(void)
{
driver_remove_file(&xen_pcibk_pci_driver.driver, &driver_attr_new_slot);
@@ -1440,6 +1499,8 @@ static void pcistub_exit(void)
driver_remove_file(&xen_pcibk_pci_driver.driver, &driver_attr_quirks);
driver_remove_file(&xen_pcibk_pci_driver.driver,
&driver_attr_permissive);
+ driver_remove_file(&xen_pcibk_pci_driver.driver,
+ &driver_attr_allow_msi_enable);
driver_remove_file(&xen_pcibk_pci_driver.driver,
&driver_attr_irq_handlers);
driver_remove_file(&xen_pcibk_pci_driver.driver,
@@ -1530,6 +1591,9 @@ static int __init pcistub_init(void)
if (!err)
err = driver_create_file(&xen_pcibk_pci_driver.driver,
&driver_attr_permissive);
+ if (!err)
+ err = driver_create_file(&xen_pcibk_pci_driver.driver,
+ &driver_attr_allow_msi_enable);
if (!err)
err = driver_create_file(&xen_pcibk_pci_driver.driver,
diff --git a/drivers/xen/xen-pciback/pciback.h b/drivers/xen/xen-pciback/pciback.h
index 263c059bff90..796f949c92be 100644
--- a/drivers/xen/xen-pciback/pciback.h
+++ b/drivers/xen/xen-pciback/pciback.h
@@ -45,6 +45,7 @@ struct xen_pcibk_dev_data {
struct list_head config_fields;
struct pci_saved_state *pci_saved_state;
unsigned int permissive:1;
+ unsigned int allow_msi_enable:1;
unsigned int warned_on_write:1;
unsigned int enable_intx:1;
unsigned int isr_on:1; /* Whether the IRQ handler is installed. */
--
2.25.3