lkml.org 
[lkml]   [2018]   [Oct]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: x86/mm: Found insecure W+X mapping at address (ptrval)/0xc00a0000
On Thu, Oct 04, 2018 at 10:03:21AM +0200, Joerg Roedel wrote:
> I also triggered this when working in the PTI-x32 code. It always
> happens on a 32-bit PAE kernel for me.
>
> Tracking it down I ended up in (iirc) arch/x86/mm/pageattr.c
> function static_protections():
>
> /*
> * The BIOS area between 640k and 1Mb needs to be executable for
> * PCI BIOS based config access (CONFIG_PCI_GOBIOS) support.
> */
> #ifdef CONFIG_PCI_BIOS
> if (pcibios_enabled && within(pfn, BIOS_BEGIN >> PAGE_SHIFT, BIOS_END >> PAGE_SHIFT))
> pgprot_val(forbidden) |= _PAGE_NX;
> #endif
>
> I think that is the reason we are seeing this in that configuration.

So looking at this, BIOS_BEGIN and BIOS_END is the same range as the ISA
range:

#define ISA_START_ADDRESS 0x000a0000
#define ISA_END_ADDRESS 0x00100000

#define BIOS_BEGIN 0x000a0000
#define BIOS_END 0x00100000


and I did try marking the ISA range RO in mark_rodata_ro() but the
machine wouldn't boot after. So I'm guessing BIOS needs to write there
some crap.

--
Regards/Gruss,
Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

\
 
 \ /
  Last update: 2018-10-04 10:15    [W:0.077 / U:0.080 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site