[PATCH V2] device-assignment pci: correct pci config size default for cap version 2 endpoints

[Donald Dutile <ddutile@redhat.com>]

v2: do local boundary check with respect to legacy PCI header length,
    and don't depend on it in pci_add_capability().
  : fix compilation, and change else>2 to simple else for all other cases.

Doing device assignement using a PCIe device with it's
PCI Cap structure at offset 0xcc showed a problem in
the default size mapped for this cap-id.

The failure caused a corruption which might have gone unnoticed
otherwise.

Fix assigned_device_pci_cap_init() to set the default
size of PCIe Cap structure (cap-id 0x10) to 0x34 instead of 0x3c.
0x34 is default, min, for endpoint device with a cap version of 2.

Add check in assigned_devic_pci_cap_init() to ensure
size of Cap structure doesn't exceed legacy PCI header space,
which is where it must fit.

Signed-off-by: Donald Dutile <ddutile@redhat.com>
cc: Alex Williamson <alex.williamson@redhat.com>
cc: Michael S. Tsirkin <mst@redhat.com>
---

 hw/device-assignment.c |   19 ++++++++++++++++---
 1 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/hw/device-assignment.c b/hw/device-assignment.c
index 36ad6b0..6bb8af7 100644
--- a/hw/device-assignment.c
+++ b/hw/device-assignment.c
@@ -1419,21 +1419,34 @@ static int assigned_device_pci_cap_init(PCIDevice *pci_dev)
     }
 
     if ((pos = pci_find_cap_offset(pci_dev, PCI_CAP_ID_EXP, 0))) {
-        uint8_t version;
+        uint8_t version, size;
         uint16_t type, devctl, lnkcap, lnksta;
         uint32_t devcap;
-        int size = 0x3c; /* version 2 size */
 
         version = pci_get_byte(pci_dev->config + pos + PCI_EXP_FLAGS);
         version &= PCI_EXP_FLAGS_VERS;
         if (version == 1) {
             size = 0x14;
-        } else if (version > 2) {
+        } else if (version == 2) {
+            /* don't include slot cap/stat/ctrl 2 regs; only support endpoints */
+            size = 0x34;
+        } else {
             fprintf(stderr, "Unsupported PCI express capability version %d\n",
                     version);
             return -EINVAL;
         }
 
+	/* make sure cap struct resides in legacy hdr space */
+	if (size > PCI_CONFIG_SPACE_SIZE - pos) {
+            fprintf(stderr, "ERROR: %04x:%02x:%02x.%x "
+                    "Attempt to add PCI Cap Structure 0x%x at offset 0x%x,"
+                    "size 0x%x, which exceeds legacy PCI config space 0x%x\n",
+                    pci_find_domain(pci_dev->bus), pci_bus_num(pci_dev->bus),
+                    PCI_SLOT(pci_dev->devfn), PCI_FUNC(pci_dev->devfn),
+                    PCI_CAP_ID_EXP, pos, size, PCI_CONFIG_SPACE_SIZE);
+            return -EINVAL;
+        }
+
         if ((ret = pci_add_capability(pci_dev, PCI_CAP_ID_EXP,
                                       pos, size)) < 0) {
             return ret;