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authorKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>2015-11-02 17:24:08 -0500
committerKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>2015-12-18 10:48:34 -0500
commita396f3a210c3a61e94d6b87ec05a75d0be2a60d0 (patch)
treeebebdf4c71082028c2b5a1d4f30851192c7680dd
parentxen/pciback: Return error on XEN_PCI_OP_enable_msix when device has MSI or MSI-X enabled (diff)
downloadlinux-dev-a396f3a210c3a61e94d6b87ec05a75d0be2a60d0.tar.xz
linux-dev-a396f3a210c3a61e94d6b87ec05a75d0be2a60d0.zip
xen/pciback: Do not install an IRQ handler for MSI interrupts.
Otherwise an guest can subvert the generic MSI code to trigger an BUG_ON condition during MSI interrupt freeing: for (i = 0; i < entry->nvec_used; i++) BUG_ON(irq_has_action(entry->irq + i)); Xen PCI backed installs an IRQ handler (request_irq) for the dev->irq whenever the guest writes PCI_COMMAND_MEMORY (or PCI_COMMAND_IO) to the PCI_COMMAND register. This is done in case the device has legacy interrupts the GSI line is shared by the backend devices. To subvert the backend the guest needs to make the backend to change the dev->irq from the GSI to the MSI interrupt line, make the backend allocate an interrupt handler, and then command the backend to free the MSI interrupt and hit the BUG_ON. Since the backend only calls 'request_irq' when the guest writes to the PCI_COMMAND register the guest needs to call XEN_PCI_OP_enable_msi before any other operation. This will cause the generic MSI code to setup an MSI entry and populate dev->irq with the new PIRQ value. Then the guest can write to PCI_COMMAND PCI_COMMAND_MEMORY and cause the backend to setup an IRQ handler for dev->irq (which instead of the GSI value has the MSI pirq). See 'xen_pcibk_control_isr'. Then the guest disables the MSI: XEN_PCI_OP_disable_msi which ends up triggering the BUG_ON condition in 'free_msi_irqs' as there is an IRQ handler for the entry->irq (dev->irq). Note that this cannot be done using MSI-X as the generic code does not over-write dev->irq with the MSI-X PIRQ values. The patch inhibits setting up the IRQ handler if MSI or MSI-X (for symmetry reasons) code had been called successfully. P.S. Xen PCIBack when it sets up the device for the guest consumption ends up writting 0 to the PCI_COMMAND (see xen_pcibk_reset_device). XSA-120 addendum patch removed that - however when upstreaming said addendum we found that it caused issues with qemu upstream. That has now been fixed in qemu upstream. This is part of XSA-157 CC: stable@vger.kernel.org Reviewed-by: David Vrabel <david.vrabel@citrix.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
-rw-r--r--drivers/xen/xen-pciback/pciback_ops.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/drivers/xen/xen-pciback/pciback_ops.c b/drivers/xen/xen-pciback/pciback_ops.c
index 029f33ddb8bf..d0696ce31e9b 100644
--- a/drivers/xen/xen-pciback/pciback_ops.c
+++ b/drivers/xen/xen-pciback/pciback_ops.c
@@ -70,6 +70,13 @@ static void xen_pcibk_control_isr(struct pci_dev *dev, int reset)
enable ? "enable" : "disable");
if (enable) {
+ /*
+ * The MSI or MSI-X should not have an IRQ handler. Otherwise
+ * if the guest terminates we BUG_ON in free_msi_irqs.
+ */
+ if (dev->msi_enabled || dev->msix_enabled)
+ goto out;
+
rc = request_irq(dev_data->irq,
xen_pcibk_guest_interrupt, IRQF_SHARED,
dev_data->irq_name, dev);