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xen/pciback: Save xen_pci_op commands before processing it 

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.

CC: stable@vger.kernel.org
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Jan Beulich <JBeulich@suse.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
This commit is contained in:
Konrad Rzeszutek Wilk 2015-11-16 12:40:48 -05:00
parent be69746ec1
commit 8135cf8b09
2 changed files with 15 additions and 1 deletions
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1
drivers/xen/xen-pciback/pciback.h
View File

@ -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 {

15
drivers/xen/xen-pciback/pciback_ops.c
View File

@ -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);