Re: [PATCH -V1] x86: make executable for video bios area

wangyanqing
2011-11-16T09:34:26Z

Hi All!
Here is the result of my research, hope it is useful to resolve this question.

Notice:trace from up to down
1:pci_arch_init()

2:pci_mmcfg_early_init() ;boot without PCI_PROBE_NOEARLY

3:__pci_mmcfg_init(1);

4:pci_mmcfg_arch_init(); mmcfg need acpi

5:pci_probe = (pci_probe & ~PCI_PROBE_MASK) | PCI_PROBE_MMCONF; <== IMPORTANT: clean PCI_PROBE_BIOS away

6:pci_pcbios_init();

7:pci_probe & PCI_PROBE_BIOS ; it will fail

8:pci_find_bios() will no chance to execute

the result is:
1:pcibios_enabled will always 0
2:set_bios_x will no chance to execute, so from BIOS_BEGIN to BIOS_END is NX

lrmi:linux real mode interface project, http://sourceforge.net/projects/lrmi/
v86d use lrmi
lrmi.c:358

if (!map_file((void *)0xc0000, 0x40000,
PROT_READ | PROT_EXEC,
MAP_FIXED | MAP_SHARED, "/dev/mem", 0xc0000)) {
munmap((void *)0, 0x502);
munmap((void *)0xa0000, 0x20000);
real_mem_deinit();
return 0;
}
this function to map 000c0000-00100000 with X privilege

00000000-00001000 rw-s 00000000 00:01 822 /dev/mem
00009000-0000a000 r-xp 00001000 00:01 912 /sbin/v86d
00010000-00050000 rwxp 00000000 00:01 818 /dev/zero
000a0000-000c0000 rw-s 000a0000 00:01 822 /dev/mem
000c0000-00100000 r-xs 000c0000 00:01 822 /dev/mem
08048000-0804c000 r-xp 00001000 00:01 912 /sbin/v86d
0804c000-0804d000 rw-p 00004000 00:01 912 /sbin/v86d
b779a000-b779b000 r-xp 00000000 00:00 0 [vdso]
bfac2000-bfae3000 rw-p 00000000 00:00 0 [stack]

At last we get the reason that my machine hang with black screen
The reason is when I boot with ACPI, BIOS_BEGIN to BIOS_END is NX,
then v86d try to map 0xc0000 to 0x100000 with executable privilege,
it mmap success(mem.c:300, mmap_mem haven't check whether it is illegal),
but the pages between BIOS_BEGIN and BIOS_END is NX at all, so it hang!

Question:
1:boot with ACPI make BIOS area NX on X86, is that what we want?
2:mmap_mem haven't check whether it is illegal the mmap target address, right?

Thanks