Re: [PATCH 0/2] Enable page table write protection

["Wang, Jian J" <jian.j.wang@intel.com>]

Yes, I validated them manually with JTAG debug tool. 

 if ((L3PageTable[Index3] & IA32_PG_PS) != 0) {
   // 1G page. Split to 2M.
   L2PageTable = AllocatePages (1);
   ASSERT (L2PageTable != NULL);
    PhysicalAddress = L3PageTable[Index3] & PAGING_1G_ADDRESS_MASK_64;
    for (Index = 0; Index < EFI_PAGE_SIZE/sizeof (UINT64); ++Index) {
     L2PageTable[Index] = PhysicalAddress  | AddressEncMask |
                          IA32_PG_PS | IA32_PG_P | IA32_PG_RW;
     PhysicalAddress += SIZE_2MB;
   }
   L3PageTable[Index3] = (UINT64) (UINTN) L2PageTable | AddressEncMask |
                                          IA32_PG_P | IA32_PG_RW;
   SetPageReadOnly (PageTableBase, (EFI_PHYSICAL_ADDRESS)(UINTN)L2PageTable);
 }

The newly allocated page table is set in the SetPageReadOnly() itself recursively, like
above code in which L2PageTable is allocated and then set it to be read-only after
initializing the table content.

> -----Original Message-----
> From: Yao, Jiewen
> Sent: Wednesday, November 29, 2017 5:16 PM
> To: Wang, Jian J <jian.j.wang@intel.com>
> Cc: edk2-devel@lists.01.org
> Subject: Re: [edk2] [PATCH 0/2] Enable page table write protection
> 
> Thanks.
> 
> May I know if this is validated in uefi shell, that all page table is readonly?
> 
> I did not find the code to set new allocated split page to be readonly. Can you
> give me a hand on that?
> 
> thank you!
> Yao, Jiewen
> 
> 
> > 在 2017年11月29日，下午4:47，Jian J Wang <jian.j.wang@intel.com> 写
> 道：
> >
> > Write Protect feature (CR0.WP) is always enabled in driver
> UefiCpuPkg/CpuDxe.
> > But the memory pages used for page table are not set as read-only in the
> driver
> > DxeIplPeim, after the paging is setup. This might jeopardize the page table
> > integrity if there's buffer overflow occured in other part of system.
> >
> > This patch series will change this situation by clearing R/W bit in page attribute
> > of the pages used as page table.
> >
> > Validation works include booting Windows (10/server 2016) and Linux
> (Fedora/Ubuntu)
> > on OVMF and Intel real platform.
> >
> > Jian J Wang (2):
> > UefiCpuPkg/CpuDxe: Check CR0.WP before changing page table
> > MdeModulePkg/DxeIpl: Mark page table as read-only
> >
> > MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c | 166
> +++++++++++++++++++++++
> > MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h |  14 ++
> > UefiCpuPkg/CpuDxe/CpuPageTable.c                 |  65 ++++++++-
> > 3 files changed, 241 insertions(+), 4 deletions(-)
> >
> > --
> > 2.14.1.windows.1
> >
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