[v1] Enable page table write protection

[edk2] [PATCH 0/2] Enable page table write protection

Posted by Jian J Wang 6 years, 4 months ago

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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Re: [edk2] [PATCH 0/2] Enable page table write protection

Posted by Yao, Jiewen 6 years, 4 months ago

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
> 
> _______________________________________________
> edk2-devel mailing list
> edk2-devel@lists.01.org
> https://lists.01.org/mailman/listinfo/edk2-devel
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Re: [edk2] [PATCH 0/2] Enable page table write protection

Posted by Wang, Jian J 6 years, 4 months ago

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
> >
> > _______________________________________________
> > edk2-devel mailing list
> > edk2-devel@lists.01.org
> > https://lists.01.org/mailman/listinfo/edk2-devel
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Re: [edk2] [PATCH 0/2] Enable page table write protection

Posted by Yao, Jiewen 6 years, 4 months ago

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
>>> 
>>> _______________________________________________
>>> edk2-devel mailing list
>>> edk2-devel@lists.01.org
>>> https://lists.01.org/mailman/listinfo/edk2-devel
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Re: [edk2] [PATCH 0/2] Enable page table write protection

Posted by Wang, Jian J 6 years, 4 months ago

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
> >>>
> >>> _______________________________________________
> >>> edk2-devel mailing list
> >>> edk2-devel@lists.01.org
> >>> https://lists.01.org/mailman/listinfo/edk2-devel
_______________________________________________
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Re: [edk2] [PATCH 0/2] Enable page table write protection

Posted by Yao, Jiewen 6 years, 4 months ago

I do think we need update CPU driver to protect new allocated split page.

If you verified in shell env, I think it will exposed, please add a test to trigger page split in CPU driver.

I recommend to write some unit test to parse page table in shell.

thank you!
Yao, Jiewen


> 在 2017年11月29日，下午8:15，Wang, Jian J <jian.j.wang@intel.com> 写道：
> 
> 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
>>>>> 
>>>>> _______________________________________________
>>>>> edk2-devel mailing list
>>>>> edk2-devel@lists.01.org
>>>>> https://lists.01.org/mailman/listinfo/edk2-devel
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Re: [edk2] [PATCH 0/2] Enable page table write protection

Posted by Wang, Jian J 6 years, 4 months ago

I did think of protecting new page table in cpu driver. But I think there's risks
to do it, which is that there might be a chance that, whenever you're trying to
mark one page used as page table to be read-only, you need to split its page
table in advance, and again and again, until all page tables are for 4KB pages.

Although this is a rare case, or the page table "split" will just happen for a few
times, it will slow down the boot process a little bit anyway. So I though  it's
safer not to protect new page tables created after DxeIpl.

Maybe it's just over worrying about it. Maybe we just need to add a PCD to 
turn on/off it just in case. Do you have any ideas in mind?

> -----Original Message-----
> From: Yao, Jiewen
> Sent: Wednesday, November 29, 2017 9:35 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
> 
> I do think we need update CPU driver to protect new allocated split page.
> 
> If you verified in shell env, I think it will exposed, please add a test to trigger
> page split in CPU driver.
> 
> I recommend to write some unit test to parse page table in shell.
> 
> thank you!
> Yao, Jiewen
> 
> 
> > 在 2017年11月29日，下午8:15，Wang, Jian J <jian.j.wang@intel.com> 写
> 道：
> >
> > 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
> >>>>>
> >>>>> _______________________________________________
> >>>>> edk2-devel mailing list
> >>>>> edk2-devel@lists.01.org
> >>>>> https://lists.01.org/mailman/listinfo/edk2-devel
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Re: [edk2] [PATCH 0/2] Enable page table write protection

Posted by Yao, Jiewen 6 years, 4 months ago

-- whenever you're trying to mark one page used as page table to be read-only, you need to split its page table in advance
[Jiewen] Sorry, I do not quite understand the problem statement.
To set a page to be ReadOnly, you just flip the R/W bit in the page entry.
The step I expect is:
1) You split page table.
2) Fill the data structure in the new entry.
3) Flip R/W bit (<== This is the new step).
4) FlushPageTable.

Thank you
Yao Jiewen

> -----Original Message-----
> From: Wang, Jian J
> Sent: Thursday, November 30, 2017 8:44 AM
> To: Yao, Jiewen <jiewen.yao@intel.com>
> Cc: edk2-devel@lists.01.org
> Subject: RE: [edk2] [PATCH 0/2] Enable page table write protection
> 
> I did think of protecting new page table in cpu driver. But I think there's risks
> to do it, which is that there might be a chance that, whenever you're trying to
> mark one page used as page table to be read-only, you need to split its page
> table in advance, and again and again, until all page tables are for 4KB pages.
> 
> Although this is a rare case, or the page table "split" will just happen for a few
> times, it will slow down the boot process a little bit anyway. So I though  it's
> safer not to protect new page tables created after DxeIpl.
> 
> Maybe it's just over worrying about it. Maybe we just need to add a PCD to
> turn on/off it just in case. Do you have any ideas in mind?
> 
> > -----Original Message-----
> > From: Yao, Jiewen
> > Sent: Wednesday, November 29, 2017 9:35 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
> >
> > I do think we need update CPU driver to protect new allocated split page.
> >
> > If you verified in shell env, I think it will exposed, please add a test to trigger
> > page split in CPU driver.
> >
> > I recommend to write some unit test to parse page table in shell.
> >
> > thank you!
> > Yao, Jiewen
> >
> >
> > > 在 2017年11月29日，下午8:15，Wang, Jian J <jian.j.wang@intel.com>
> 写
> > 道：
> > >
> > > 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
> > >>>>>
> > >>>>> _______________________________________________
> > >>>>> edk2-devel mailing list
> > >>>>> edk2-devel@lists.01.org
> > >>>>> https://lists.01.org/mailman/listinfo/edk2-devel
_______________________________________________
edk2-devel mailing list
edk2-devel@lists.01.org
https://lists.01.org/mailman/listinfo/edk2-devel

Re: [edk2] [PATCH 0/2] Enable page table write protection

Posted by Wang, Jian J 6 years, 4 months ago

When you split page tables, you need to allocate new pages for new page table.
Since you have new page tables added, you need to mark them to be read-only
as well, right? When you do this, the page table for the memory newly allocated
might still needs to be split. This is the worst case but there's still chance of it,
right? We cannot guarantee, theoretically, the page table for the newly allocated
page tables is in the same as just split ones. So, in worst case, once we want to
mark new page table to be read-only, we need to split the page table managing
those memory, and if we need to do split, we need to allocate more new pages.
This might fall into a recursive situation until all the smallest page table are created.
In practice it's almost impossible to let it happen but the chances are we will fall into 
such recursive situation more than one level.

> -----Original Message-----
> From: Yao, Jiewen
> Sent: Thursday, November 30, 2017 8:52 AM
> 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
> 
> -- whenever you're trying to mark one page used as page table to be read-only,
> you need to split its page table in advance
> [Jiewen] Sorry, I do not quite understand the problem statement.
> To set a page to be ReadOnly, you just flip the R/W bit in the page entry.
> The step I expect is:
> 1) You split page table.
> 2) Fill the data structure in the new entry.
> 3) Flip R/W bit (<== This is the new step).
> 4) FlushPageTable.
> 
> Thank you
> Yao Jiewen
> 
> > -----Original Message-----
> > From: Wang, Jian J
> > Sent: Thursday, November 30, 2017 8:44 AM
> > To: Yao, Jiewen <jiewen.yao@intel.com>
> > Cc: edk2-devel@lists.01.org
> > Subject: RE: [edk2] [PATCH 0/2] Enable page table write protection
> >
> > I did think of protecting new page table in cpu driver. But I think there's risks
> > to do it, which is that there might be a chance that, whenever you're trying to
> > mark one page used as page table to be read-only, you need to split its page
> > table in advance, and again and again, until all page tables are for 4KB pages.
> >
> > Although this is a rare case, or the page table "split" will just happen for a few
> > times, it will slow down the boot process a little bit anyway. So I though  it's
> > safer not to protect new page tables created after DxeIpl.
> >
> > Maybe it's just over worrying about it. Maybe we just need to add a PCD to
> > turn on/off it just in case. Do you have any ideas in mind?
> >
> > > -----Original Message-----
> > > From: Yao, Jiewen
> > > Sent: Wednesday, November 29, 2017 9:35 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
> > >
> > > I do think we need update CPU driver to protect new allocated split page.
> > >
> > > If you verified in shell env, I think it will exposed, please add a test to trigger
> > > page split in CPU driver.
> > >
> > > I recommend to write some unit test to parse page table in shell.
> > >
> > > thank you!
> > > Yao, Jiewen
> > >
> > >
> > > > 在 2017年11月29日，下午8:15，Wang, Jian J <jian.j.wang@intel.com>
> > 写
> > > 道：
> > > >
> > > > 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
> > > >>>>>
> > > >>>>> _______________________________________________
> > > >>>>> edk2-devel mailing list
> > > >>>>> edk2-devel@lists.01.org
> > > >>>>> https://lists.01.org/mailman/listinfo/edk2-devel
_______________________________________________
edk2-devel mailing list
edk2-devel@lists.01.org
https://lists.01.org/mailman/listinfo/edk2-devel

Re: [edk2] [PATCH 0/2] Enable page table write protection

Posted by Yao, Jiewen 6 years, 4 months ago

Can you just allocate 1 more page for split?
If new one need split, you can just use the additional page.
If not, you can free it later.

Thank you
Yao Jiewen


> -----Original Message-----
> From: Wang, Jian J
> Sent: Thursday, November 30, 2017 9:17 AM
> To: Yao, Jiewen <jiewen.yao@intel.com>
> Cc: edk2-devel@lists.01.org
> Subject: RE: [edk2] [PATCH 0/2] Enable page table write protection
> 
> When you split page tables, you need to allocate new pages for new page table.
> Since you have new page tables added, you need to mark them to be read-only
> as well, right? When you do this, the page table for the memory newly allocated
> might still needs to be split. This is the worst case but there's still chance of it,
> right? We cannot guarantee, theoretically, the page table for the newly allocated
> page tables is in the same as just split ones. So, in worst case, once we want to
> mark new page table to be read-only, we need to split the page table managing
> those memory, and if we need to do split, we need to allocate more new pages.
> This might fall into a recursive situation until all the smallest page table are
> created.
> In practice it's almost impossible to let it happen but the chances are we will fall
> into
> such recursive situation more than one level.
> 
> > -----Original Message-----
> > From: Yao, Jiewen
> > Sent: Thursday, November 30, 2017 8:52 AM
> > 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
> >
> > -- whenever you're trying to mark one page used as page table to be read-only,
> > you need to split its page table in advance
> > [Jiewen] Sorry, I do not quite understand the problem statement.
> > To set a page to be ReadOnly, you just flip the R/W bit in the page entry.
> > The step I expect is:
> > 1) You split page table.
> > 2) Fill the data structure in the new entry.
> > 3) Flip R/W bit (<== This is the new step).
> > 4) FlushPageTable.
> >
> > Thank you
> > Yao Jiewen
> >
> > > -----Original Message-----
> > > From: Wang, Jian J
> > > Sent: Thursday, November 30, 2017 8:44 AM
> > > To: Yao, Jiewen <jiewen.yao@intel.com>
> > > Cc: edk2-devel@lists.01.org
> > > Subject: RE: [edk2] [PATCH 0/2] Enable page table write protection
> > >
> > > I did think of protecting new page table in cpu driver. But I think there's risks
> > > to do it, which is that there might be a chance that, whenever you're trying to
> > > mark one page used as page table to be read-only, you need to split its page
> > > table in advance, and again and again, until all page tables are for 4KB pages.
> > >
> > > Although this is a rare case, or the page table "split" will just happen for a few
> > > times, it will slow down the boot process a little bit anyway. So I though  it's
> > > safer not to protect new page tables created after DxeIpl.
> > >
> > > Maybe it's just over worrying about it. Maybe we just need to add a PCD to
> > > turn on/off it just in case. Do you have any ideas in mind?
> > >
> > > > -----Original Message-----
> > > > From: Yao, Jiewen
> > > > Sent: Wednesday, November 29, 2017 9:35 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
> > > >
> > > > I do think we need update CPU driver to protect new allocated split page.
> > > >
> > > > If you verified in shell env, I think it will exposed, please add a test to trigger
> > > > page split in CPU driver.
> > > >
> > > > I recommend to write some unit test to parse page table in shell.
> > > >
> > > > thank you!
> > > > Yao, Jiewen
> > > >
> > > >
> > > > > 在 2017年11月29日，下午8:15，Wang, Jian J <jian.j.wang@intel.com>
> > > 写
> > > > 道：
> > > > >
> > > > > 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
> > > > >>>>>
> > > > >>>>> _______________________________________________
> > > > >>>>> edk2-devel mailing list
> > > > >>>>> edk2-devel@lists.01.org
> > > > >>>>> https://lists.01.org/mailman/listinfo/edk2-devel
_______________________________________________
edk2-devel mailing list
edk2-devel@lists.01.org
https://lists.01.org/mailman/listinfo/edk2-devel

Re: [edk2] [PATCH 0/2] Enable page table write protection

Posted by Yao, Jiewen 6 years, 4 months ago

Clarify my word below:

Can you just predict and pre-allocate additional pages for future split in worst case?
If new one need split, you can just use the additional pages.
If not, you can free them later.

For example, you can allocate 2M aligned memory for new pages, for make sure they are in same page directory.

Thank you
Yao Jiewen

> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Yao,
> Jiewen
> Sent: Thursday, November 30, 2017 9:36 AM
> 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
> 
> Can you just allocate 1 more page for split?
> If new one need split, you can just use the additional page.
> If not, you can free it later.
> 
> Thank you
> Yao Jiewen
> 
> 
> > -----Original Message-----
> > From: Wang, Jian J
> > Sent: Thursday, November 30, 2017 9:17 AM
> > To: Yao, Jiewen <jiewen.yao@intel.com>
> > Cc: edk2-devel@lists.01.org
> > Subject: RE: [edk2] [PATCH 0/2] Enable page table write protection
> >
> > When you split page tables, you need to allocate new pages for new page
> table.
> > Since you have new page tables added, you need to mark them to be read-only
> > as well, right? When you do this, the page table for the memory newly
> allocated
> > might still needs to be split. This is the worst case but there's still chance of it,
> > right? We cannot guarantee, theoretically, the page table for the newly
> allocated
> > page tables is in the same as just split ones. So, in worst case, once we want to
> > mark new page table to be read-only, we need to split the page table managing
> > those memory, and if we need to do split, we need to allocate more new pages.
> > This might fall into a recursive situation until all the smallest page table are
> > created.
> > In practice it's almost impossible to let it happen but the chances are we will fall
> > into
> > such recursive situation more than one level.
> >
> > > -----Original Message-----
> > > From: Yao, Jiewen
> > > Sent: Thursday, November 30, 2017 8:52 AM
> > > 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
> > >
> > > -- whenever you're trying to mark one page used as page table to be
> read-only,
> > > you need to split its page table in advance
> > > [Jiewen] Sorry, I do not quite understand the problem statement.
> > > To set a page to be ReadOnly, you just flip the R/W bit in the page entry.
> > > The step I expect is:
> > > 1) You split page table.
> > > 2) Fill the data structure in the new entry.
> > > 3) Flip R/W bit (<== This is the new step).
> > > 4) FlushPageTable.
> > >
> > > Thank you
> > > Yao Jiewen
> > >
> > > > -----Original Message-----
> > > > From: Wang, Jian J
> > > > Sent: Thursday, November 30, 2017 8:44 AM
> > > > To: Yao, Jiewen <jiewen.yao@intel.com>
> > > > Cc: edk2-devel@lists.01.org
> > > > Subject: RE: [edk2] [PATCH 0/2] Enable page table write protection
> > > >
> > > > I did think of protecting new page table in cpu driver. But I think there's
> risks
> > > > to do it, which is that there might be a chance that, whenever you're trying
> to
> > > > mark one page used as page table to be read-only, you need to split its page
> > > > table in advance, and again and again, until all page tables are for 4KB
> pages.
> > > >
> > > > Although this is a rare case, or the page table "split" will just happen for a
> few
> > > > times, it will slow down the boot process a little bit anyway. So I though
> it's
> > > > safer not to protect new page tables created after DxeIpl.
> > > >
> > > > Maybe it's just over worrying about it. Maybe we just need to add a PCD to
> > > > turn on/off it just in case. Do you have any ideas in mind?
> > > >
> > > > > -----Original Message-----
> > > > > From: Yao, Jiewen
> > > > > Sent: Wednesday, November 29, 2017 9:35 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
> > > > >
> > > > > I do think we need update CPU driver to protect new allocated split page.
> > > > >
> > > > > If you verified in shell env, I think it will exposed, please add a test to
> trigger
> > > > > page split in CPU driver.
> > > > >
> > > > > I recommend to write some unit test to parse page table in shell.
> > > > >
> > > > > thank you!
> > > > > Yao, Jiewen
> > > > >
> > > > >
> > > > > > 在 2017年11月29日，下午8:15，Wang, Jian J
> <jian.j.wang@intel.com>
> > > > 写
> > > > > 道：
> > > > > >
> > > > > > 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
> > > > > >>>>>
> > > > > >>>>> _______________________________________________
> > > > > >>>>> edk2-devel mailing list
> > > > > >>>>> edk2-devel@lists.01.org
> > > > > >>>>> https://lists.01.org/mailman/listinfo/edk2-devel
> _______________________________________________
> edk2-devel mailing list
> edk2-devel@lists.01.org
> https://lists.01.org/mailman/listinfo/edk2-devel
_______________________________________________
edk2-devel mailing list
edk2-devel@lists.01.org
https://lists.01.org/mailman/listinfo/edk2-devel

Re: [edk2] [PATCH 0/2] Enable page table write protection

Posted by Wang, Jian J 6 years, 4 months ago

Good idea. I think it will highly reduce the possibility but not solve it still.
The dilemma here is: do we need to take care of it? This issue exists in theory
but has not yet been encountered in practice.

> -----Original Message-----
> From: Yao, Jiewen
> Sent: Thursday, November 30, 2017 9:36 AM
> 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
> 
> Can you just allocate 1 more page for split?
> If new one need split, you can just use the additional page.
> If not, you can free it later.
> 
> Thank you
> Yao Jiewen
> 
> 
> > -----Original Message-----
> > From: Wang, Jian J
> > Sent: Thursday, November 30, 2017 9:17 AM
> > To: Yao, Jiewen <jiewen.yao@intel.com>
> > Cc: edk2-devel@lists.01.org
> > Subject: RE: [edk2] [PATCH 0/2] Enable page table write protection
> >
> > When you split page tables, you need to allocate new pages for new page
> table.
> > Since you have new page tables added, you need to mark them to be read-only
> > as well, right? When you do this, the page table for the memory newly
> allocated
> > might still needs to be split. This is the worst case but there's still chance of it,
> > right? We cannot guarantee, theoretically, the page table for the newly
> allocated
> > page tables is in the same as just split ones. So, in worst case, once we want to
> > mark new page table to be read-only, we need to split the page table
> managing
> > those memory, and if we need to do split, we need to allocate more new
> pages.
> > This might fall into a recursive situation until all the smallest page table are
> > created.
> > In practice it's almost impossible to let it happen but the chances are we will
> fall
> > into
> > such recursive situation more than one level.
> >
> > > -----Original Message-----
> > > From: Yao, Jiewen
> > > Sent: Thursday, November 30, 2017 8:52 AM
> > > 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
> > >
> > > -- whenever you're trying to mark one page used as page table to be read-
> only,
> > > you need to split its page table in advance
> > > [Jiewen] Sorry, I do not quite understand the problem statement.
> > > To set a page to be ReadOnly, you just flip the R/W bit in the page entry.
> > > The step I expect is:
> > > 1) You split page table.
> > > 2) Fill the data structure in the new entry.
> > > 3) Flip R/W bit (<== This is the new step).
> > > 4) FlushPageTable.
> > >
> > > Thank you
> > > Yao Jiewen
> > >
> > > > -----Original Message-----
> > > > From: Wang, Jian J
> > > > Sent: Thursday, November 30, 2017 8:44 AM
> > > > To: Yao, Jiewen <jiewen.yao@intel.com>
> > > > Cc: edk2-devel@lists.01.org
> > > > Subject: RE: [edk2] [PATCH 0/2] Enable page table write protection
> > > >
> > > > I did think of protecting new page table in cpu driver. But I think there's
> risks
> > > > to do it, which is that there might be a chance that, whenever you're trying
> to
> > > > mark one page used as page table to be read-only, you need to split its
> page
> > > > table in advance, and again and again, until all page tables are for 4KB
> pages.
> > > >
> > > > Although this is a rare case, or the page table "split" will just happen for a
> few
> > > > times, it will slow down the boot process a little bit anyway. So I though
> it's
> > > > safer not to protect new page tables created after DxeIpl.
> > > >
> > > > Maybe it's just over worrying about it. Maybe we just need to add a PCD to
> > > > turn on/off it just in case. Do you have any ideas in mind?
> > > >
> > > > > -----Original Message-----
> > > > > From: Yao, Jiewen
> > > > > Sent: Wednesday, November 29, 2017 9:35 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
> > > > >
> > > > > I do think we need update CPU driver to protect new allocated split page.
> > > > >
> > > > > If you verified in shell env, I think it will exposed, please add a test to
> trigger
> > > > > page split in CPU driver.
> > > > >
> > > > > I recommend to write some unit test to parse page table in shell.
> > > > >
> > > > > thank you!
> > > > > Yao, Jiewen
> > > > >
> > > > >
> > > > > > 在 2017年11月29日，下午8:15，Wang, Jian J
> <jian.j.wang@intel.com>
> > > > 写
> > > > > 道：
> > > > > >
> > > > > > 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
> > > > > >>>>>
> > > > > >>>>> _______________________________________________
> > > > > >>>>> edk2-devel mailing list
> > > > > >>>>> edk2-devel@lists.01.org
> > > > > >>>>> https://lists.01.org/mailman/listinfo/edk2-devel
_______________________________________________
edk2-devel mailing list
edk2-devel@lists.01.org
https://lists.01.org/mailman/listinfo/edk2-devel

Re: [edk2] [PATCH 0/2] Enable page table write protection

Posted by Yao, Jiewen 6 years, 4 months ago

Clarify my word below:

Can you just predict and pre-allocate additional pages for future split in worst case?
If new one need split, you can just use the additional pages.
If not, you can free them later.

For example, you can allocate 2M aligned memory for new pages, for make sure they are in same page directory.

I think it can resolve the problem.
The key is to pre-calculate how many pages are involved in the worst case.

Thank you
Yao Jiewen


> -----Original Message-----
> From: Wang, Jian J
> Sent: Thursday, November 30, 2017 9:47 AM
> To: Yao, Jiewen <jiewen.yao@intel.com>
> Cc: edk2-devel@lists.01.org
> Subject: RE: [edk2] [PATCH 0/2] Enable page table write protection
> 
> Good idea. I think it will highly reduce the possibility but not solve it still.
> The dilemma here is: do we need to take care of it? This issue exists in theory
> but has not yet been encountered in practice.
> 
> > -----Original Message-----
> > From: Yao, Jiewen
> > Sent: Thursday, November 30, 2017 9:36 AM
> > 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
> >
> > Can you just allocate 1 more page for split?
> > If new one need split, you can just use the additional page.
> > If not, you can free it later.
> >
> > Thank you
> > Yao Jiewen
> >
> >
> > > -----Original Message-----
> > > From: Wang, Jian J
> > > Sent: Thursday, November 30, 2017 9:17 AM
> > > To: Yao, Jiewen <jiewen.yao@intel.com>
> > > Cc: edk2-devel@lists.01.org
> > > Subject: RE: [edk2] [PATCH 0/2] Enable page table write protection
> > >
> > > When you split page tables, you need to allocate new pages for new page
> > table.
> > > Since you have new page tables added, you need to mark them to be
> read-only
> > > as well, right? When you do this, the page table for the memory newly
> > allocated
> > > might still needs to be split. This is the worst case but there's still chance of it,
> > > right? We cannot guarantee, theoretically, the page table for the newly
> > allocated
> > > page tables is in the same as just split ones. So, in worst case, once we want
> to
> > > mark new page table to be read-only, we need to split the page table
> > managing
> > > those memory, and if we need to do split, we need to allocate more new
> > pages.
> > > This might fall into a recursive situation until all the smallest page table are
> > > created.
> > > In practice it's almost impossible to let it happen but the chances are we will
> > fall
> > > into
> > > such recursive situation more than one level.
> > >
> > > > -----Original Message-----
> > > > From: Yao, Jiewen
> > > > Sent: Thursday, November 30, 2017 8:52 AM
> > > > 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
> > > >
> > > > -- whenever you're trying to mark one page used as page table to be read-
> > only,
> > > > you need to split its page table in advance
> > > > [Jiewen] Sorry, I do not quite understand the problem statement.
> > > > To set a page to be ReadOnly, you just flip the R/W bit in the page entry.
> > > > The step I expect is:
> > > > 1) You split page table.
> > > > 2) Fill the data structure in the new entry.
> > > > 3) Flip R/W bit (<== This is the new step).
> > > > 4) FlushPageTable.
> > > >
> > > > Thank you
> > > > Yao Jiewen
> > > >
> > > > > -----Original Message-----
> > > > > From: Wang, Jian J
> > > > > Sent: Thursday, November 30, 2017 8:44 AM
> > > > > To: Yao, Jiewen <jiewen.yao@intel.com>
> > > > > Cc: edk2-devel@lists.01.org
> > > > > Subject: RE: [edk2] [PATCH 0/2] Enable page table write protection
> > > > >
> > > > > I did think of protecting new page table in cpu driver. But I think there's
> > risks
> > > > > to do it, which is that there might be a chance that, whenever you're
> trying
> > to
> > > > > mark one page used as page table to be read-only, you need to split its
> > page
> > > > > table in advance, and again and again, until all page tables are for 4KB
> > pages.
> > > > >
> > > > > Although this is a rare case, or the page table "split" will just happen for a
> > few
> > > > > times, it will slow down the boot process a little bit anyway. So I though
> > it's
> > > > > safer not to protect new page tables created after DxeIpl.
> > > > >
> > > > > Maybe it's just over worrying about it. Maybe we just need to add a PCD
> to
> > > > > turn on/off it just in case. Do you have any ideas in mind?
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Yao, Jiewen
> > > > > > Sent: Wednesday, November 29, 2017 9:35 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
> > > > > >
> > > > > > I do think we need update CPU driver to protect new allocated split
> page.
> > > > > >
> > > > > > If you verified in shell env, I think it will exposed, please add a test to
> > trigger
> > > > > > page split in CPU driver.
> > > > > >
> > > > > > I recommend to write some unit test to parse page table in shell.
> > > > > >
> > > > > > thank you!
> > > > > > Yao, Jiewen
> > > > > >
> > > > > >
> > > > > > > 在 2017年11月29日，下午8:15，Wang, Jian J
> > <jian.j.wang@intel.com>
> > > > > 写
> > > > > > 道：
> > > > > > >
> > > > > > > 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
> > > > > > >>>>>
> > > > > > >>>>> _______________________________________________
> > > > > > >>>>> edk2-devel mailing list
> > > > > > >>>>> edk2-devel@lists.01.org
> > > > > > >>>>> https://lists.01.org/mailman/listinfo/edk2-devel
_______________________________________________
edk2-devel mailing list
edk2-devel@lists.01.org
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Re: [edk2] [PATCH 0/2] Enable page table write protection

Posted by Wang, Jian J 6 years, 4 months ago

That's a better idea. Maybe we don't to free them but just reserve it for future uses.
The reserved 2MB page table can manage 1GB memory. I think in BIOS time typical
memory usage I observed is far less than that.

> -----Original Message-----
> From: Yao, Jiewen
> Sent: Thursday, November 30, 2017 9:59 AM
> 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
> 
> Clarify my word below:
> 
> Can you just predict and pre-allocate additional pages for future split in worst
> case?
> If new one need split, you can just use the additional pages.
> If not, you can free them later.
> 
> For example, you can allocate 2M aligned memory for new pages, for make sure
> they are in same page directory.
> 
> I think it can resolve the problem.
> The key is to pre-calculate how many pages are involved in the worst case.
> 
> Thank you
> Yao Jiewen
> 
> 
> > -----Original Message-----
> > From: Wang, Jian J
> > Sent: Thursday, November 30, 2017 9:47 AM
> > To: Yao, Jiewen <jiewen.yao@intel.com>
> > Cc: edk2-devel@lists.01.org
> > Subject: RE: [edk2] [PATCH 0/2] Enable page table write protection
> >
> > Good idea. I think it will highly reduce the possibility but not solve it still.
> > The dilemma here is: do we need to take care of it? This issue exists in theory
> > but has not yet been encountered in practice.
> >
> > > -----Original Message-----
> > > From: Yao, Jiewen
> > > Sent: Thursday, November 30, 2017 9:36 AM
> > > 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
> > >
> > > Can you just allocate 1 more page for split?
> > > If new one need split, you can just use the additional page.
> > > If not, you can free it later.
> > >
> > > Thank you
> > > Yao Jiewen
> > >
> > >
> > > > -----Original Message-----
> > > > From: Wang, Jian J
> > > > Sent: Thursday, November 30, 2017 9:17 AM
> > > > To: Yao, Jiewen <jiewen.yao@intel.com>
> > > > Cc: edk2-devel@lists.01.org
> > > > Subject: RE: [edk2] [PATCH 0/2] Enable page table write protection
> > > >
> > > > When you split page tables, you need to allocate new pages for new page
> > > table.
> > > > Since you have new page tables added, you need to mark them to be
> > read-only
> > > > as well, right? When you do this, the page table for the memory newly
> > > allocated
> > > > might still needs to be split. This is the worst case but there's still chance of
> it,
> > > > right? We cannot guarantee, theoretically, the page table for the newly
> > > allocated
> > > > page tables is in the same as just split ones. So, in worst case, once we
> want
> > to
> > > > mark new page table to be read-only, we need to split the page table
> > > managing
> > > > those memory, and if we need to do split, we need to allocate more new
> > > pages.
> > > > This might fall into a recursive situation until all the smallest page table are
> > > > created.
> > > > In practice it's almost impossible to let it happen but the chances are we
> will
> > > fall
> > > > into
> > > > such recursive situation more than one level.
> > > >
> > > > > -----Original Message-----
> > > > > From: Yao, Jiewen
> > > > > Sent: Thursday, November 30, 2017 8:52 AM
> > > > > 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
> > > > >
> > > > > -- whenever you're trying to mark one page used as page table to be
> read-
> > > only,
> > > > > you need to split its page table in advance
> > > > > [Jiewen] Sorry, I do not quite understand the problem statement.
> > > > > To set a page to be ReadOnly, you just flip the R/W bit in the page entry.
> > > > > The step I expect is:
> > > > > 1) You split page table.
> > > > > 2) Fill the data structure in the new entry.
> > > > > 3) Flip R/W bit (<== This is the new step).
> > > > > 4) FlushPageTable.
> > > > >
> > > > > Thank you
> > > > > Yao Jiewen
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Wang, Jian J
> > > > > > Sent: Thursday, November 30, 2017 8:44 AM
> > > > > > To: Yao, Jiewen <jiewen.yao@intel.com>
> > > > > > Cc: edk2-devel@lists.01.org
> > > > > > Subject: RE: [edk2] [PATCH 0/2] Enable page table write protection
> > > > > >
> > > > > > I did think of protecting new page table in cpu driver. But I think there's
> > > risks
> > > > > > to do it, which is that there might be a chance that, whenever you're
> > trying
> > > to
> > > > > > mark one page used as page table to be read-only, you need to split its
> > > page
> > > > > > table in advance, and again and again, until all page tables are for 4KB
> > > pages.
> > > > > >
> > > > > > Although this is a rare case, or the page table "split" will just happen for
> a
> > > few
> > > > > > times, it will slow down the boot process a little bit anyway. So I though
> > > it's
> > > > > > safer not to protect new page tables created after DxeIpl.
> > > > > >
> > > > > > Maybe it's just over worrying about it. Maybe we just need to add a
> PCD
> > to
> > > > > > turn on/off it just in case. Do you have any ideas in mind?
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: Yao, Jiewen
> > > > > > > Sent: Wednesday, November 29, 2017 9:35 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
> > > > > > >
> > > > > > > I do think we need update CPU driver to protect new allocated split
> > page.
> > > > > > >
> > > > > > > If you verified in shell env, I think it will exposed, please add a test to
> > > trigger
> > > > > > > page split in CPU driver.
> > > > > > >
> > > > > > > I recommend to write some unit test to parse page table in shell.
> > > > > > >
> > > > > > > thank you!
> > > > > > > Yao, Jiewen
> > > > > > >
> > > > > > >
> > > > > > > > 在 2017年11月29日，下午8:15，Wang, Jian J
> > > <jian.j.wang@intel.com>
> > > > > > 写
> > > > > > > 道：
> > > > > > > >
> > > > > > > > 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
> > > > > > > >>>>>
> > > > > > > >>>>> _______________________________________________
> > > > > > > >>>>> edk2-devel mailing list
> > > > > > > >>>>> edk2-devel@lists.01.org
> > > > > > > >>>>> https://lists.01.org/mailman/listinfo/edk2-devel
_______________________________________________
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Re: [edk2] [PATCH 0/2] Enable page table write protection

Posted by Andrew Fish 6 years, 4 months ago


> On Nov 29, 2017, at 5:16 PM, Wang, Jian J <jian.j.wang@intel.com> wrote:
> 
> When you split page tables, you need to allocate new pages for new page table.
> Since you have new page tables added, you need to mark them to be read-only
> as well, right? When you do this, the page table for the memory newly allocated
> might still needs to be split. This is the worst case but there's still chance of it,
> right? We cannot guarantee, theoretically, the page table for the newly allocated
> page tables is in the same as just split ones. So, in worst case, once we want to
> mark new page table to be read-only, we need to split the page table managing
> those memory, and if we need to do split, we need to allocate more new pages.
> This might fall into a recursive situation until all the smallest page table are created.
> In practice it's almost impossible to let it happen but the chances are we will fall into 
> such recursive situation more than one level.
> 

Why not just have the page table update code turn off the write protect when it is modifying tables, and then turn it back on? Or am I missing something?

Thanks,

Andrew Fish

>> -----Original Message-----
>> From: Yao, Jiewen
>> Sent: Thursday, November 30, 2017 8:52 AM
>> 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
>> 
>> -- whenever you're trying to mark one page used as page table to be read-only,
>> you need to split its page table in advance
>> [Jiewen] Sorry, I do not quite understand the problem statement.
>> To set a page to be ReadOnly, you just flip the R/W bit in the page entry.
>> The step I expect is:
>> 1) You split page table.
>> 2) Fill the data structure in the new entry.
>> 3) Flip R/W bit (<== This is the new step).
>> 4) FlushPageTable.
>> 
>> Thank you
>> Yao Jiewen
>> 
>>> -----Original Message-----
>>> From: Wang, Jian J
>>> Sent: Thursday, November 30, 2017 8:44 AM
>>> To: Yao, Jiewen <jiewen.yao@intel.com>
>>> Cc: edk2-devel@lists.01.org
>>> Subject: RE: [edk2] [PATCH 0/2] Enable page table write protection
>>> 
>>> I did think of protecting new page table in cpu driver. But I think there's risks
>>> to do it, which is that there might be a chance that, whenever you're trying to
>>> mark one page used as page table to be read-only, you need to split its page
>>> table in advance, and again and again, until all page tables are for 4KB pages.
>>> 
>>> Although this is a rare case, or the page table "split" will just happen for a few
>>> times, it will slow down the boot process a little bit anyway. So I though  it's
>>> safer not to protect new page tables created after DxeIpl.
>>> 
>>> Maybe it's just over worrying about it. Maybe we just need to add a PCD to
>>> turn on/off it just in case. Do you have any ideas in mind?
>>> 
>>>> -----Original Message-----
>>>> From: Yao, Jiewen
>>>> Sent: Wednesday, November 29, 2017 9:35 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
>>>> 
>>>> I do think we need update CPU driver to protect new allocated split page.
>>>> 
>>>> If you verified in shell env, I think it will exposed, please add a test to trigger
>>>> page split in CPU driver.
>>>> 
>>>> I recommend to write some unit test to parse page table in shell.
>>>> 
>>>> thank you!
>>>> Yao, Jiewen
>>>> 
>>>> 
>>>>> 在 2017年11月29日，下午8:15，Wang, Jian J <jian.j.wang@intel.com>
>>> 写
>>>> 道：
>>>>> 
>>>>> 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
>>>>>>>>> 
>>>>>>>>> _______________________________________________
>>>>>>>>> edk2-devel mailing list
>>>>>>>>> edk2-devel@lists.01.org
>>>>>>>>> https://lists.01.org/mailman/listinfo/edk2-devel
> _______________________________________________
> edk2-devel mailing list
> edk2-devel@lists.01.org
> https://lists.01.org/mailman/listinfo/edk2-devel

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Re: [edk2] [PATCH 0/2] Enable page table write protection

Posted by Wang, Jian J 6 years, 4 months ago

Hi Andrew,

I did turn on/off write protection when I update page attributes. What we're discussing
is the worst case in which protecting the newly added page table will fall into a very deep
recursive loop. This is possible in theory but not sure it will really happen in practice.

> -----Original Message-----
> From: afish@apple.com [mailto:afish@apple.com]
> Sent: Thursday, November 30, 2017 9:38 AM
> To: Wang, Jian J <jian.j.wang@intel.com>
> Cc: Yao, Jiewen <jiewen.yao@intel.com>; edk2-devel@lists.01.org
> Subject: Re: [edk2] [PATCH 0/2] Enable page table write protection
> 
> 
> 
> > On Nov 29, 2017, at 5:16 PM, Wang, Jian J <jian.j.wang@intel.com> wrote:
> >
> > When you split page tables, you need to allocate new pages for new page
> table.
> > Since you have new page tables added, you need to mark them to be read-only
> > as well, right? When you do this, the page table for the memory newly
> allocated
> > might still needs to be split. This is the worst case but there's still chance of it,
> > right? We cannot guarantee, theoretically, the page table for the newly
> allocated
> > page tables is in the same as just split ones. So, in worst case, once we want to
> > mark new page table to be read-only, we need to split the page table
> managing
> > those memory, and if we need to do split, we need to allocate more new
> pages.
> > This might fall into a recursive situation until all the smallest page table are
> created.
> > In practice it's almost impossible to let it happen but the chances are we will
> fall into
> > such recursive situation more than one level.
> >
> 
> Why not just have the page table update code turn off the write protect when it
> is modifying tables, and then turn it back on? Or am I missing something?
> 
> Thanks,
> 
> Andrew Fish
> 
> >> -----Original Message-----
> >> From: Yao, Jiewen
> >> Sent: Thursday, November 30, 2017 8:52 AM
> >> 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
> >>
> >> -- whenever you're trying to mark one page used as page table to be read-
> only,
> >> you need to split its page table in advance
> >> [Jiewen] Sorry, I do not quite understand the problem statement.
> >> To set a page to be ReadOnly, you just flip the R/W bit in the page entry.
> >> The step I expect is:
> >> 1) You split page table.
> >> 2) Fill the data structure in the new entry.
> >> 3) Flip R/W bit (<== This is the new step).
> >> 4) FlushPageTable.
> >>
> >> Thank you
> >> Yao Jiewen
> >>
> >>> -----Original Message-----
> >>> From: Wang, Jian J
> >>> Sent: Thursday, November 30, 2017 8:44 AM
> >>> To: Yao, Jiewen <jiewen.yao@intel.com>
> >>> Cc: edk2-devel@lists.01.org
> >>> Subject: RE: [edk2] [PATCH 0/2] Enable page table write protection
> >>>
> >>> I did think of protecting new page table in cpu driver. But I think there's risks
> >>> to do it, which is that there might be a chance that, whenever you're trying
> to
> >>> mark one page used as page table to be read-only, you need to split its page
> >>> table in advance, and again and again, until all page tables are for 4KB pages.
> >>>
> >>> Although this is a rare case, or the page table "split" will just happen for a
> few
> >>> times, it will slow down the boot process a little bit anyway. So I though  it's
> >>> safer not to protect new page tables created after DxeIpl.
> >>>
> >>> Maybe it's just over worrying about it. Maybe we just need to add a PCD to
> >>> turn on/off it just in case. Do you have any ideas in mind?
> >>>
> >>>> -----Original Message-----
> >>>> From: Yao, Jiewen
> >>>> Sent: Wednesday, November 29, 2017 9:35 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
> >>>>
> >>>> I do think we need update CPU driver to protect new allocated split page.
> >>>>
> >>>> If you verified in shell env, I think it will exposed, please add a test to
> trigger
> >>>> page split in CPU driver.
> >>>>
> >>>> I recommend to write some unit test to parse page table in shell.
> >>>>
> >>>> thank you!
> >>>> Yao, Jiewen
> >>>>
> >>>>
> >>>>> 在 2017年11月29日，下午8:15，Wang, Jian J
> <jian.j.wang@intel.com>
> >>> 写
> >>>> 道：
> >>>>>
> >>>>> 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
> >>>>>>>>>
> >>>>>>>>> _______________________________________________
> >>>>>>>>> edk2-devel mailing list
> >>>>>>>>> edk2-devel@lists.01.org
> >>>>>>>>> https://lists.01.org/mailman/listinfo/edk2-devel
> > _______________________________________________
> > edk2-devel mailing list
> > edk2-devel@lists.01.org
> > https://lists.01.org/mailman/listinfo/edk2-devel

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Re: [edk2] [PATCH 0/2] Enable page table write protection

Posted by Laszlo Ersek 6 years, 4 months ago

Hi Jian,

On 11/29/17 09:46, Jian J Wang wrote:
> 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(-)
> 

thanks for the CC -- I'd like to test this feature.

Is it OK if I wait 1-2 days first, to see if there is review feedback
that requires a v2?

Thanks!
Laszlo
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Re: [edk2] [PATCH 0/2] Enable page table write protection

Posted by Wang, Jian J 6 years, 4 months ago

There's already issue found. So there must be v2. Please wait for it.

> -----Original Message-----
> From: Laszlo Ersek [mailto:lersek@redhat.com]
> Sent: Wednesday, November 29, 2017 8:39 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
> 
> Hi Jian,
> 
> On 11/29/17 09:46, Jian J Wang wrote:
> > 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(-)
> >
> 
> thanks for the CC -- I'd like to test this feature.
> 
> Is it OK if I wait 1-2 days first, to see if there is review feedback
> that requires a v2?
> 
> Thanks!
> Laszlo
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