x86, pci, mrst: Add extra sanity check in walking the PCI extended cap chain

commit f82c3d71d6fd2e6a3e3416f09099e29087e39abf upstream.

The fixed bar capability structure is searched in PCI extended
configuration space.  We need to make sure there is a valid capability
ID to begin with otherwise, the search code may stuck in a infinite
loop which results in boot hang.  This patch adds additional check for
cap ID 0, which is also invalid, and indicates end of chain.

End of chain is supposed to have all fields zero, but that doesn't
seem to always be the case in the field.

Suggested-by: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
LKML-Reference: <1279306706-27087-1-git-send-email-jacob.jun.pan@linux.intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/arch/x86/pci/mrst.c b/arch/x86/pci/mrst.c
index 1cdc02cf8fa49e159cdd4696766abad56b50c13b..1699ea80e911ee15de30701bb2bef01ca1b458fd 100644 (file)
--- a/arch/x86/pci/mrst.c
+++ b/arch/x86/pci/mrst.c
@@ -66,8 +66,9 @@ static int fixed_bar_cap(struct pci_bus *bus, unsigned int devfn)
                                          devfn, pos, 4, &pcie_cap))
                        return 0;
 
-               if (pcie_cap == 0xffffffff)
-                       return 0;
+               if (PCI_EXT_CAP_ID(pcie_cap) == 0x0000 ||
+                       PCI_EXT_CAP_ID(pcie_cap) == 0xffff)
+                       break;
 
                if (PCI_EXT_CAP_ID(pcie_cap) == PCI_EXT_CAP_ID_VNDR) {
                        raw_pci_ext_ops->read(pci_domain_nr(bus), bus->number,
@@ -76,7 +77,7 @@ static int fixed_bar_cap(struct pci_bus *bus, unsigned int devfn)
                                return pos;
                }
 
-               pos = pcie_cap >> 20;
+               pos = PCI_EXT_CAP_NEXT(pcie_cap);
        }
 
        return 0;