[3.19.y-ckt stable] Patch "xen/pciback: Save xen_pci_op commands before processing it" has been added to the 3.19.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    xen/pciback: Save xen_pci_op commands before processing it

to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.19.y-queue

This patch is scheduled to be released in version 3.19.8-ckt13.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.19.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From 9bac474dd0a8de272210e0cf0171a73dc8a49953 Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Date: Mon, 16 Nov 2015 12:40:48 -0500
Subject: xen/pciback: Save xen_pci_op commands before processing it

commit 8135cf8b092723dbfcc611fe6fdcb3a36c9951c5 upstream.

Double fetch vulnerabilities that happen when a variable is
fetched twice from shared memory but a security check is only
performed the first time.

The xen_pcibk_do_op function performs a switch statements on the op->cmd
value which is stored in shared memory. Interestingly this can result
in a double fetch vulnerability depending on the performed compiler
optimization.

This patch fixes it by saving the xen_pci_op command before
processing it. We also use 'barrier' to make sure that the
compiler does not perform any optimization.

This is part of XSA155.

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Signed-off-by: Jan Beulich <JBeulich at suse.com>
Signed-off-by: David Vrabel <david.vrabel at citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/xen/xen-pciback/pciback.h     |  1 +
 drivers/xen/xen-pciback/pciback_ops.c | 15 ++++++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/xen-pciback/pciback.h b/drivers/xen/xen-pciback/pciback.h
index 58e38d5..4d529f3 100644
--- a/drivers/xen/xen-pciback/pciback.h
+++ b/drivers/xen/xen-pciback/pciback.h
@@ -37,6 +37,7 @@ struct xen_pcibk_device {
 	struct xen_pci_sharedinfo *sh_info;
 	unsigned long flags;
 	struct work_struct op_work;
+	struct xen_pci_op op;
 };

 struct xen_pcibk_dev_data {
diff --git a/drivers/xen/xen-pciback/pciback_ops.c b/drivers/xen/xen-pciback/pciback_ops.c
index c4a0666..a0e0e3e 100644
--- a/drivers/xen/xen-pciback/pciback_ops.c
+++ b/drivers/xen/xen-pciback/pciback_ops.c
@@ -298,9 +298,11 @@ void xen_pcibk_do_op(struct work_struct *data)
 		container_of(data, struct xen_pcibk_device, op_work);
 	struct pci_dev *dev;
 	struct xen_pcibk_dev_data *dev_data = NULL;
-	struct xen_pci_op *op = &pdev->sh_info->op;
+	struct xen_pci_op *op = &pdev->op;
 	int test_intx = 0;

+	*op = pdev->sh_info->op;
+	barrier();
 	dev = xen_pcibk_get_pci_dev(pdev, op->domain, op->bus, op->devfn);

 	if (dev == NULL)
@@ -342,6 +344,17 @@ void xen_pcibk_do_op(struct work_struct *data)
 		if ((dev_data->enable_intx != test_intx))
 			xen_pcibk_control_isr(dev, 0 /* no reset */);
 	}
+	pdev->sh_info->op.err = op->err;
+	pdev->sh_info->op.value = op->value;
+#ifdef CONFIG_PCI_MSI
+	if (op->cmd == XEN_PCI_OP_enable_msix && op->err == 0) {
+		unsigned int i;
+
+		for (i = 0; i < op->value; i++)
+			pdev->sh_info->op.msix_entries[i].vector =
+				op->msix_entries[i].vector;
+	}
+#endif
 	/* Tell the driver domain that we're done. */
 	wmb();
 	clear_bit(_XEN_PCIF_active, (unsigned long *)&pdev->sh_info->flags);
--
1.9.1