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

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

It's in the DxeIplPeim.

By the way, there's an issue in this patch. I forgot to protect page table for 32-bit mode.
So this patch works only for 64-bit mode. I'll add it in v2 patch. 

> -----Original Message-----
> From: Yao, Jiewen
> Sent: Wednesday, November 29, 2017 6:56 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
> 
> Is this code in CPU driver?
> 
> thank you!
> Yao, Jiewen
> 
> 
> > 在 2017年11月29日，下午6:24，Wang, Jian J <jian.j.wang@intel.com> 写
> 道：
> >
> > 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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