qemu/pci: check constant registers on load

Add "cmask" table of constant register masks: if a bit is not writeable
and is set in cmask table, this bit is checked on load.  An attempt to
load an image that would change such a register causes load to fail.
Use this table to make sure that load does not modify registers that
guest can not change (directly or indirectly).

Note: we can't just assume that read-only registers never change,
because the guest could change a register indirectly.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/hw/pci.h b/hw/pci.h
index d07477f..8b5edef 100644
--- a/hw/pci.h
+++ b/hw/pci.h
@@ -101,6 +101,7 @@ typedef struct PCIIORegion {
 #define  PCI_COMMAND_MASTER	0x4	/* Enable bus master */
 #define PCI_STATUS              0x06    /* 16 bits */
 #define PCI_REVISION_ID         0x08    /* 8 bits  */
+#define PCI_CLASS_PROG		0x09	/* Reg. Level Programming Interface */
 #define PCI_CLASS_DEVICE        0x0a    /* Device class */
 #define PCI_CACHE_LINE_SIZE	0x0c	/* 8 bits */
 #define PCI_LATENCY_TIMER	0x0d	/* 8 bits */
@@ -159,6 +160,10 @@ struct PCIDevice {
     /* PCI config space */
     uint8_t config[PCI_CONFIG_SPACE_SIZE];
 
+    /* Used to enable config checks on load. Note that writeable bits are
+     * never checked even if set in cmask. */
+    uint8_t cmask[PCI_CONFIG_SPACE_SIZE];
+
     /* Used to implement R/W bytes */
     uint8_t wmask[PCI_CONFIG_SPACE_SIZE];