Comment 12 for bug 931371

Luckily my first guess was correct. The following patch needs to be applied to SeaBIOS:

commit 3c5fcec00ce1317cda56d549259550fcc018c834
Author: Kevin O'Connor <email address hidden>
Date: Sat Oct 1 12:35:32 2011 -0400

    Fix alignment bug in pci_bios_init_root_regions().

    If there are no memory allocations for a given type then the "max" bar
    size is zero. However, ALIGN_DOWN does not handle an alignment of
    zero properly. Catch and handle the zero case.

    Signed-off-by: Kevin O'Connor <email address hidden>

diff --git a/src/pciinit.c b/src/pciinit.c
index a857da0..0d8758e 100644
--- a/src/pciinit.c
+++ b/src/pciinit.c
@@ -536,7 +536,7 @@ static void pci_bios_init_bus_bases(struct pci_bus *bus)
     }
 }

-#define ROOT_BASE(top, sum, align) ALIGN_DOWN((top)-(sum),(align))
+#define ROOT_BASE(top, sum, max) ALIGN_DOWN((top)-(sum),(max) ?: 1)

 static int pci_bios_init_root_regions(u32 start, u32 end)
 {

I tested this by applying this patch to seabios 0.6.2-0ubuntu2 and it completely cures the problem.