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xen: limit guest control of PCI command register
Otherwise the guest can abuse that control to cause e.g. PCIe
Unsupported Request responses (by disabling memory and/or I/O decoding
and subsequently causing [CPU side] accesses to the respective address
ranges), which (depending on system configuration) may be fatal to the
host.
This is CVE-2015-2756 / XSA-126.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
--- a/tools/qemu-xen/hw/xen/xen_pt.c
+++ b/tools/qemu-xen/hw/xen/xen_pt.c
@@ -388,7 +388,7 @@ static const MemoryRegionOps ops = {
.write = xen_pt_bar_write,
};
-static int xen_pt_register_regions(XenPCIPassthroughState *s)
+static int xen_pt_register_regions(XenPCIPassthroughState *s, uint16_t *cmd)
{
int i = 0;
XenHostPCIDevice *d = &s->real_device;
@@ -406,6 +406,7 @@ static int xen_pt_register_regions(XenPC
if (r->type & XEN_HOST_PCI_REGION_TYPE_IO) {
type = PCI_BASE_ADDRESS_SPACE_IO;
+ *cmd |= PCI_COMMAND_IO;
} else {
type = PCI_BASE_ADDRESS_SPACE_MEMORY;
if (r->type & XEN_HOST_PCI_REGION_TYPE_PREFETCH) {
@@ -414,6 +415,7 @@ static int xen_pt_register_regions(XenPC
if (r->type & XEN_HOST_PCI_REGION_TYPE_MEM_64) {
type |= PCI_BASE_ADDRESS_MEM_TYPE_64;
}
+ *cmd |= PCI_COMMAND_MEMORY;
}
memory_region_init_io(&s->bar[i], OBJECT(s), &ops, &s->dev,
@@ -638,6 +640,7 @@ static int xen_pt_initfn(PCIDevice *d)
XenPCIPassthroughState *s = DO_UPCAST(XenPCIPassthroughState, dev, d);
int rc = 0;
uint8_t machine_irq = 0;
+ uint16_t cmd = 0;
int pirq = XEN_PT_UNASSIGNED_PIRQ;
/* register real device */
@@ -672,7 +675,7 @@ static int xen_pt_initfn(PCIDevice *d)
s->io_listener = xen_pt_io_listener;
/* Handle real device's MMIO/PIO BARs */
- xen_pt_register_regions(s);
+ xen_pt_register_regions(s, &cmd);
/* reinitialize each config register to be emulated */
if (xen_pt_config_init(s)) {
@@ -736,6 +739,11 @@ static int xen_pt_initfn(PCIDevice *d)
}
out:
+ if (cmd) {
+ xen_host_pci_set_word(&s->real_device, PCI_COMMAND,
+ pci_get_word(d->config + PCI_COMMAND) | cmd);
+ }
+
memory_listener_register(&s->memory_listener, &address_space_memory);
memory_listener_register(&s->io_listener, &address_space_io);
XEN_PT_LOG(d,
--- a/tools/qemu-xen/hw/xen/xen_pt_config_init.c
+++ b/tools/qemu-xen/hw/xen/xen_pt_config_init.c
@@ -286,23 +286,6 @@ static int xen_pt_irqpin_reg_init(XenPCI
}
/* Command register */
-static int xen_pt_cmd_reg_read(XenPCIPassthroughState *s, XenPTReg *cfg_entry,
- uint16_t *value, uint16_t valid_mask)
-{
- XenPTRegInfo *reg = cfg_entry->reg;
- uint16_t valid_emu_mask = 0;
- uint16_t emu_mask = reg->emu_mask;
-
- if (s->is_virtfn) {
- emu_mask |= PCI_COMMAND_MEMORY;
- }
-
- /* emulate word register */
- valid_emu_mask = emu_mask & valid_mask;
- *value = XEN_PT_MERGE_VALUE(*value, cfg_entry->data, ~valid_emu_mask);
-
- return 0;
-}
static int xen_pt_cmd_reg_write(XenPCIPassthroughState *s, XenPTReg *cfg_entry,
uint16_t *val, uint16_t dev_value,
uint16_t valid_mask)
@@ -310,18 +293,13 @@ static int xen_pt_cmd_reg_write(XenPCIPa
XenPTRegInfo *reg = cfg_entry->reg;
uint16_t writable_mask = 0;
uint16_t throughable_mask = 0;
- uint16_t emu_mask = reg->emu_mask;
-
- if (s->is_virtfn) {
- emu_mask |= PCI_COMMAND_MEMORY;
- }
/* modify emulate register */
writable_mask = ~reg->ro_mask & valid_mask;
cfg_entry->data = XEN_PT_MERGE_VALUE(*val, cfg_entry->data, writable_mask);
/* create value for writing to I/O device register */
- throughable_mask = ~emu_mask & valid_mask;
+ throughable_mask = ~reg->emu_mask & valid_mask;
if (*val & PCI_COMMAND_INTX_DISABLE) {
throughable_mask |= PCI_COMMAND_INTX_DISABLE;
@@ -605,9 +583,9 @@ static XenPTRegInfo xen_pt_emu_reg_heade
.size = 2,
.init_val = 0x0000,
.ro_mask = 0xF880,
- .emu_mask = 0x0740,
+ .emu_mask = 0x0743,
.init = xen_pt_common_reg_init,
- .u.w.read = xen_pt_cmd_reg_read,
+ .u.w.read = xen_pt_word_reg_read,
.u.w.write = xen_pt_cmd_reg_write,
},
/* Capabilities Pointer reg */
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