From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753946AbcARDZA (ORCPT ); Sun, 17 Jan 2016 22:25:00 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:59430 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753179AbcARDWF (ORCPT ); Sun, 17 Jan 2016 22:22:05 -0500 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "David Vrabel" , "Konrad Rzeszutek Wilk" Date: Mon, 18 Jan 2016 03:18:35 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 27/70] xen/pciback: Do not install an IRQ handler for MSI interrupts. In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.247 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.76-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Konrad Rzeszutek Wilk commit a396f3a210c3a61e94d6b87ec05a75d0be2a60d0 upstream. 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 Reviewed-by: David Vrabel Signed-off-by: Konrad Rzeszutek Wilk Signed-off-by: Ben Hutchings --- drivers/xen/xen-pciback/pciback_ops.c | 7 +++++++ 1 file changed, 7 insertions(+) --- a/drivers/xen/xen-pciback/pciback_ops.c +++ b/drivers/xen/xen-pciback/pciback_ops.c @@ -68,6 +68,13 @@ static void xen_pcibk_control_isr(struct 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);