[PATCHv6 04/12] qemu/pci: check constant registers on load

Michael S. Tsirkin
2009-06-21T16:52:33Z

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>
---
hw/pci.c | 26 +++++++++++++++++++++++++-
hw/pci.h | 5 +++++
2 files changed, 30 insertions(+), 1 deletions(-)

diff --git a/hw/pci.c b/hw/pci.c
index 72ca27b..d8fa439 100644
--- a/hw/pci.c
+++ b/hw/pci.c
@@ -136,13 +136,19 @@ void pci_device_save(PCIDevice *s, QEMUFile *f)

int pci_device_load(PCIDevice *s, QEMUFile *f)
{
+ uint8_t config[PCI_CONFIG_SPACE_SIZE];
uint32_t version_id;
int i;

version_id = qemu_get_be32(f);
if (version_id > 2)
return -EINVAL;
- qemu_get_buffer(f, s->config, 256);
+ qemu_get_buffer(f, config, sizeof config);
+ for (i = 0; i < sizeof config; ++i)
+ if ((config[i] ^ s->config[i]) & s->cmask[i] & ~s->wmask[i])
+ return -EINVAL;
+ memcpy(s->config, config, sizeof config);
+
pci_update_mappings(s);

if (version_id >= 2)
@@ -237,6 +243,18 @@ int pci_assign_devaddr(const char *addr, int *domp, int *busp, unsigned *slotp)
return pci_parse_devaddr(devaddr, domp, busp, slotp);
}

+static void pci_init_cmask(PCIDevice *dev)
+{
+ pci_set_word(dev->cmask + PCI_VENDOR_ID, 0xffff);
+ pci_set_word(dev->cmask + PCI_DEVICE_ID, 0xffff);
+ dev->cmask[PCI_STATUS] = PCI_STATUS_CAP_LIST;
+ dev->cmask[PCI_REVISION_ID] = 0xff;
+ dev->cmask[PCI_CLASS_PROG] = 0xff;
+ pci_set_word(dev->cmask + PCI_CLASS_DEVICE, 0xffff);
+ dev->cmask[PCI_HEADER_TYPE] = 0xff;
+ dev->cmask[PCI_CAPABILITY_LIST] = 0xff;
+}
+
static void pci_init_wmask(PCIDevice *dev)
{
int i;
@@ -267,6 +285,7 @@ static PCIDevice *do_pci_register_device(PCIDevice *pci_dev, PCIBus *bus,
pstrcpy(pci_dev->name, sizeof(pci_dev->name), name);
memset(pci_dev->irq_state, 0, sizeof(pci_dev->irq_state));
pci_set_default_subsystem_id(pci_dev);
+ pci_init_cmask(pci_dev);
pci_init_wmask(pci_dev);

if (!config_read)
@@ -366,6 +385,7 @@ void pci_register_bar(PCIDevice *pci_dev, int region_num,
}
*(uint32_t *)(pci_dev->config + addr) = cpu_to_le32(type);
*(uint32_t *)(pci_dev->wmask + addr) = cpu_to_le32(wmask);
+ *(uint32_t *)(pci_dev->cmask + addr) = 0xffffffff;
}

static void pci_update_mappings(PCIDevice *d)
@@ -900,6 +920,8 @@ int pci_add_capability(PCIDevice *pdev, uint8_t cap_id, uint8_t size)
memset(pdev->used + offset, 0xFF, size);
/* Make capability read-only by default */
memset(pdev->wmask + offset, 0, size);
+ /* Check capability by default */
+ memset(pdev->cmask + offset, 0xFF, size);
return offset;
}

@@ -912,6 +934,8 @@ void pci_del_capability(PCIDevice *pdev, uint8_t cap_id, uint8_t size)
pdev->config[prev] = pdev->config[offset + PCI_CAP_LIST_NEXT];
/* Make capability writeable again */
memset(pdev->wmask + offset, 0xff, size);
+ /* Clear cmask as device-specific registers can't be checked */
+ memset(pdev->cmask + offset, 0, size);
memset(pdev->used + offset, 0, size);

if (!pdev->config[PCI_CAPABILITY_LIST])
diff --git a/hw/pci.h b/hw/pci.h
index 7172d81..558e18f 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];

--
1.6.2.2