Re: [PATCH v4 0/7] MdeModulePkg/DxeCore: increased memory protection

[Laszlo Ersek <lersek@redhat.com>]

On 02/27/17 15:38, Ard Biesheuvel wrote:
> Hello all,
> 
> First of all, thanks for the reviews and regression testing. However, I did
> not add the tested-by tags nor some of the R-b's, given the changes in this v4.
> 
> This series implements a memory protection policy that removes all executable
> permissions from writable memory regions, which greatly enhances security.
> It is based on Jiewen's recent work, which is a step in the right direction,
> but still leaves most of memory exploitable due to the default R+W+X
> permissions.
> 
> The idea is that the implementation of the CPU arch protocol goes over the
> memory map and removes exec permissions from all regions that are not already
> marked as 'code. This requires some preparatory work to ensure that the DxeCore
> itself is covered by a BootServicesCode region, not a BootServicesData region.
> Exec permissions are re-granted selectively, when the PE/COFF loader allocates
> the space for it. Combined with Jiewen's code/data split, this removes all
> RWX mapped regions.
> 
> Changes since v3:
> - mandate that the same policy applies to EfiConventionalMemory regions and
>   EfiBootServicesData regions: they are unlikely to differ in practice, and
>   dealing with that corner case greatly complicates the implementation, given
>   the way DxeCore allocates memory for itself in the implementation of the page
>   and pool allocation routines.
> - apply the EfiConventionalMemory policy to untested RAM regions in the GCD
>   memory space map: without this, we may still have a large region of RAM that
>   is exploitable, and it also removes the need to apply memory protections in
>   PromoteMemoryResource (), which is very difficult to achieve without a major
>   restructuring of the code due to the way locking is implemented here.
> - add missing ApplyMemoryProtectionPolicy() call to CoreAddMemoryDescriptor()
> - use CoreAcquireLockOrFail() on gMemoryLock for CoreAllocatePoolPages (#4)
> - incorporate feedback from Liming (#2, #6)
> - add patch to enable the NX memory protection policy for ArmVirtPkg (#7)
> 
> Changes since v2:
> - added patch to make EBC use EfiBootServicesCode pool allocations for thunks
> - redefine PCD according to Jiewen's feedback, including default value
> - use sorted memory map and merge adjacent entries with the same policy, to
>   prevent unnecessary page table splitting
> - ignore policy when executing in SMM
> - refactor the logic for managing permission attributes of pool allocations
> - added some R-b's
> 
> Changes since v1:
> - allocate code pages for PE/COFF images in PeiCore, so that DxeCore pages have
>   the expected memory type (as suggested by Jiewen)
> - add patch to inhibit page table updates while syncing the GCD memory space
>   map with the page tables
> - add PCD to set memory protection policy, which allows the policy for reserved
>   and ACPI/NVS memory to be configured separately
> - move attribute manipulation into DxeCore page allocation code: this way, we
>   should be able to solve the EBC case by allocating BootServicesCode pool
>   memory explicitly.
> 
> Series can be found here:
> https://git.linaro.org/people/ard.biesheuvel/uefi-next.git/log/?h=memprot-take2-v4
> 
> Ard Biesheuvel (7):
>   ArmPkg/CpuDxe: ignore attribute changes during SyncCacheConfig()
>   MdeModulePkg/PeiCore: allocate BootServicesCode memory for PE/COFF
>     images
>   MdeModulePkg/EbcDxe: use EfiBootServicesCode memory for thunks
>   MdeModulePkg/DxeCore: use separate lock for pool allocations
>   MdeModulePkg: define PCD for DXE memory protection policy
>   MdeModulePkg/DxeCore: implement memory protection policy
>   ArmVirtPkg/ArmVirt.dsc.inc: enable NX memory protection for all
>     platforms
> 
>  ArmPkg/Drivers/CpuDxe/CpuDxe.c                     |   3 +
>  ArmPkg/Drivers/CpuDxe/CpuDxe.h                     |   1 +
>  ArmPkg/Drivers/CpuDxe/CpuMmuCommon.c               |   4 +
>  ArmVirtPkg/ArmVirt.dsc.inc                         |   6 +
>  MdeModulePkg/Core/Dxe/DxeMain.h                    |  24 ++
>  MdeModulePkg/Core/Dxe/DxeMain.inf                  |   1 +
>  MdeModulePkg/Core/Dxe/Mem/Page.c                   |   7 +
>  MdeModulePkg/Core/Dxe/Mem/Pool.c                   |  65 +++-
>  MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c      | 371 +++++++++++++++++++-
>  MdeModulePkg/Core/Pei/Image/Image.c                |  23 +-
>  MdeModulePkg/MdeModulePkg.dec                      |  32 ++
>  MdeModulePkg/Universal/EbcDxe/AArch64/EbcSupport.c |   2 +-
>  MdeModulePkg/Universal/EbcDxe/EbcInt.c             |  23 ++
>  MdeModulePkg/Universal/EbcDxe/EbcInt.h             |  14 +
>  MdeModulePkg/Universal/EbcDxe/Ia32/EbcSupport.c    |   2 +-
>  MdeModulePkg/Universal/EbcDxe/Ipf/EbcSupport.c     |   2 +-
>  MdeModulePkg/Universal/EbcDxe/X64/EbcSupport.c     |   2 +-
>  17 files changed, 558 insertions(+), 24 deletions(-)
> 

I regression-tested this series for x86 / OVMF as under v3, with the zero PCD default, and experienced no issues.

However, v4 breaks booting Fedora 24 on my Mustang (aarch64/KVM):

-----------------
[Bds]Booting Fedora
FSOpen: Open '\EFI\fedora\shim.efi' Success
[Bds] DevicePath expand: HD(1,MBR,0xDB4976D3,0x800,0x64000)/\EFI\fedora\shim.efi -> PciRoot(0x0)/Pci(0x1,0x1)/Pci(0x0,0x0)/Scsi(0x1,0x0)/HD(1,MBR,0xDB4976D3,0x800,0x64000)/\EFI\fedora\shim.efi
[Security] 3rd party image[0] can be loaded after EndOfDxe: PciRoot(0x0)/Pci(0x1,0x1)/Pci(0x0,0x0)/Scsi(0x1,0x0)/HD(1,MBR,0xDB4976D3,0x800,0x64000)/\EFI\fedora\shim.efi.
InstallProtocolInterface: [EfiLoadedImageProtocol] 13A6D2AC0
Loading driver at 0x001382F4000 EntryPoint=0x001382F4148
Loading driver at 0x001382F4000 EntryPoint=0x001382F4148 
InstallProtocolInterface: [EfiLoadedImageDevicePathProtocol] 138CDBD98
ProtectUefiImageCommon - 0x3A6D2AC0
  - 0x00000001382F4000 - 0x00000000000CBAE0
!!!!!!!!  ProtectUefiImageCommon - Section Alignment(0x20) is incorrect  !!!!!!!!
FSOpen: Open '\EFI\fedora\grubaa64.efi' Success


Synchronous Exception at 0x00000001380F7400

  X0 0x000000013A6EEA98   X1 0x000000013BFF0018   X2 0x00000001380F7400   X3 0x00000000000FD000
  X4 0x0000000000000000   X5 0x0000000000000000   X6 0x0000000138362AF4   X7 0x0000000000000000
  X8 0x000000013C01F548   X9 0x0000000200000000  X10 0x00000001380F6000  X11 0x00000001382F3FFF
 X12 0x0000000000000000  X13 0x0000000000000008  X14 0x0000000000000000  X15 0x0000000000000000
 X16 0x000000013EC6ABD0  X17 0x0000000000000000  X18 0x0000000000000000  X19 0x0000000138CDB698
 X20 0x000000013A746E18  X21 0x0000000000000000  X22 0x0000000000000000  X23 0x0000000000000000
 X24 0x0000000000000000  X25 0x0000000000000000  X26 0x0000000000000000  X27 0x0000000000000000
 X28 0x0000000000000000   FP 0x000000013EC6AA50   LR 0x00000001382F80F8  

  V0 0xAFAFAFAFAFAFAFAF AFAFAFAFAFAFAFAF   V1 0x6963702F66666666 6666666666666666
  V2 0x697363732F312C31 406567646972622D   V3 0x0000000000000000 0000000000000000
  V4 0x0000000000000400 0000000000000000   V5 0x4010040140100401 4010040140100401
  V6 0x0004000000000000 0004000000000000   V7 0x0000000000000000 0000000000000000
  V8 0x0000000000000000 0000000000000000   V9 0x0000000000000000 0000000000000000
 V10 0x0000000000000000 0000000000000000  V11 0x0000000000000000 0000000000000000
 V12 0x0000000000000000 0000000000000000  V13 0x0000000000000000 0000000000000000
 V14 0x0000000000000000 0000000000000000  V15 0x0000000000000000 0000000000000000
 V16 0x0000000000000000 0000000000000000  V17 0x0000000000000000 0000000000000000
 V18 0x0000000000000000 0000000000000000  V19 0x0000000000000000 0000000000000000
 V20 0x0000000000000000 0000000000000000  V21 0x0000000000000000 0000000000000000
 V22 0x0000000000000000 0000000000000000  V23 0x0000000000000000 0000000000000000
 V24 0x0000000000000000 0000000000000000  V25 0x0000000000000000 0000000000000000
 V26 0x0000000000000000 0000000000000000  V27 0x0000000000000000 0000000000000000
 V28 0x0000000000000000 0000000000000000  V29 0x0000000000000000 0000000000000000
 V30 0x0000000000000000 0000000000000000  V31 0x0000000000000000 0000000000000000

  SP 0x000000013EC6AA50  ELR 0x00000001380F7400  SPSR 0x60000205  FPSR 0x00000000
 ESR 0x8600000E          FAR 0x00000001380F7400

 ESR : EC 0x21  IL 0x1  ISS 0x0000000E

Instruction abort: Permission fault, second level

Stack dump:
  000013EC6A950: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  000013EC6A970: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  000013EC6A990: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  000013EC6A9B0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  000013EC6A9D0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  000013EC6A9F0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  000013EC6AA10: 0000000000000000 0000000000000000 00000001380F7400 0000000060000205
  000013EC6AA30: 0000000000000000 000000008600000E 00000001380F7400 0000000400000800
> 000013EC6AA50: 000000013EC6AB50 00000001382F8198 0000000138367370 000000013A6EEA98
  000013EC6AA70: 0000000138CDB698 000FD00000000000 00000001381F5018 0000000000000000
  000013EC6AA90: 0000000000000000 00000001382F3D18 0000000000001000 0000000000000000
  000013EC6AAB0: 000000013BFF0018 000000013A4BA518 000000013A6D2F98 0000000000000000
  000013EC6AAD0: 0000000000000000 0000000000000000 00000001382F4000 00000000000CBAE0
  000013EC6AAF0: 0000000200000001 0000000000000000 000000013A6D2AC0 11D295625B1B31A1
  000013EC6AB10: 3B7269C9A0003F8E 0000000000000000 00000001382F3F98 000000003EC6AB58
  000013EC6AB30: 000000013EC6AB60 800000000000000E 000000013EC6AB80 0000000000000000
ASSERT [ArmCpuDxe] .../ArmPkg/Library/DefaultExceptionHandlerLib/AArch64/DefaultExceptionHandler.c(265): ((BOOLEAN)(0==1))
-----------------

The "shim.efi" binary is not built with the required section alignment, but that's not a problem, it only elicits a warning, and that's it. "shim.efi" still proceeds to load "grubaa64.efi".

However, "grubaa64.efi" blows up.

I experience the same with my "RHEL for ARM 7.3" guest.

In my "openSUSE Tumbleweed" guest, "shim.efi" isn't actually used; there the "opensuse" UEFI boot option refers to grub directly. There I even catch the message "Welcome to GRUB!", but then it crashes too:

---------------
[Bds]Booting opensuse
FSOpen: Open '\EFI\opensuse\grubaa64.efi' Success
[Bds] DevicePath expand: HD(1,GPT,3E62269B-A0A1-4F3C-B404-081796D9CDB4,0x800,0x4E000)/\EFI\opensuse\grubaa64.efi -> PciRoot(0x0)/Pci(0x1,0x1)/Pci(0x0,0x0)/Scsi(0x1,0x0)/HD(1,GPT,3E62269B-A0A1-4F3C-B404-081796D9CDB4,0x800,0x4E000)/\EFI\opensuse\grubaa64.efi
[Security] 3rd party image[0] can be loaded after EndOfDxe: PciRoot(0x0)/Pci(0x1,0x1)/Pci(0x0,0x0)/Scsi(0x1,0x0)/HD(1,GPT,3E62269B-A0A1-4F3C-B404-081796D9CDB4,0x800,0x4E000)/\EFI\opensuse\grubaa64.efi.
InstallProtocolInterface: [EfiLoadedImageProtocol] 13A69FD40
Loading driver at 0x00138391000 EntryPoint=0x00138391400
Loading driver at 0x00138391000 EntryPoint=0x00138391400 
InstallProtocolInterface: [EfiLoadedImageDevicePathProtocol] 138CD4E98
ProtectUefiImageCommon - 0x3A69FD40
  - 0x0000000138391000 - 0x000000000002E600
!!!!!!!!  ProtectUefiImageCommon - Section Alignment(0x200) is incorrect  !!!!!!!!
Welcome to GRUB!

^M

Synchronous Exception at 0x00000000FFFF1F3C

  X0 0x00000000FFFF3720   X1 0x00000000FFFF1F3C   X2 0x000000000000000D   X3 0x000000013839FA30
  X4 0x00000000FFFF1F3C   X5 0x00000000FFFF0800   X6 0x00000000FFFF1000   X7 0x0000000000000000
  X8 0x00000000FFFF2120   X9 0x000000000000001F  X10 0x0000000000000000  X11 0x000000013EC6A880
 X12 0x0098989800989898  X13 0x0098989800989898  X14 0x0000000000000001  X15 0x0000000000000003
 X16 0x000000013EC6ABD0  X17 0x0000000000000000  X18 0x0000000000000000  X19 0x00000000FFFF3720
 X20 0x0000000138399000  X21 0x0000000138399000  X22 0x0000000000000000  X23 0x0000000000000000
 X24 0x0000000000000000  X25 0x0000000000000000  X26 0x0000000000000000  X27 0x0000000000000000
 X28 0x0000000000000000   FP 0x000000013EC6AB60   LR 0x00000001383980CC  

  V0 0xAFAFAFAFAFAFAFAF AFAFAFAFAFAFAFAF   V1 0x6963702F66666666 6666666666666666
  V2 0x697363732F312C31 406567646972622D   V3 0x0000000000000000 0000000000000000
  V4 0x0000000000000400 0000000000000000   V5 0x4010040140100401 4010040140100401
  V6 0x0004000000000000 0004000000000000   V7 0x0000000000000000 0000000000000000
  V8 0x0000000000000000 0000000000000000   V9 0x0000000000000000 0000000000000000
 V10 0x0000000000000000 0000000000000000  V11 0x0000000000000000 0000000000000000
 V12 0x0000000000000000 0000000000000000  V13 0x0000000000000000 0000000000000000
 V14 0x0000000000000000 0000000000000000  V15 0x0000000000000000 0000000000000000
 V16 0x0000000000000000 0000000000000000  V17 0x0000000000000000 0000000000000000
 V18 0x0000000000000000 0000000000000000  V19 0x0000000000000000 0000000000000000
 V20 0x0000000000000000 0000000000000000  V21 0x0000000000000000 0000000000000000
 V22 0x0000000000000000 0000000000000000  V23 0x0000000000000000 0000000000000000
 V24 0x0000000000000000 0000000000000000  V25 0x0000000000000000 0000000000000000
 V26 0x0000000000000000 0000000000000000  V27 0x0000000000000000 0000000000000000
 V28 0x0000000000000000 0000000000000000  V29 0x0000000000000000 0000000000000000
 V30 0x0000000000000000 0000000000000000  V31 0x0000000000000000 0000000000000000

  SP 0x000000013EC6AB60  ELR 0x00000000FFFF1F3C  SPSR 0x60000205  FPSR 0x00000000
 ESR 0x8600000D          FAR 0x00000000FFFF1F3C

 ESR : EC 0x21  IL 0x1  ISS 0x0000000D

Instruction abort: Permission fault, first level

Stack dump:
  000013EC6AA60: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  000013EC6AA80: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  000013EC6AAA0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  000013EC6AAC0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  000013EC6AAE0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  000013EC6AB00: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  000013EC6AB20: 0000000000000000 0000000000000000 00000000FFFF1F3C 0000000060000205
  000013EC6AB40: 0000000000000000 000000008600000D 00000000FFFF1F3C 0000000000000000
> 000013EC6AB60: 000000013EC6AB80 0000000138399650 00000001383AAA18 0000000000000000
  000013EC6AB80: 000000013EC6ABD0 000000013EC71E50 000000013A732218 000000013A747718
  000013EC6ABA0: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  000013EC6ABC0: 0000000000000000 000000013A747718 000000013EC6AC50 000000013BA5C62C
  000013EC6ABE0: 000000013EC6AC00 0000000138CD4060 0000000138CD4068 000000013A6EE018
  000013EC6AC00: 000000013EC6AC30 000000013BA577B4 0000000000000000 0000000000000000
  000013EC6AC20: 000000013ECA83D8 0000000000000126 000000013EC6AC50 000000013A69FD18
  000013EC6AC40: 000000013A6EE018 0000000000000000 000000013EC6ACF0 000000013BA4AF88
ASSERT [ArmCpuDxe] .../ArmPkg/Library/DefaultExceptionHandlerLib/AArch64/DefaultExceptionHandler.c(265): ((BOOLEAN)(0==1))
---------------

If I revert the last patch in the series (leaving ArmVirtQemu's PCD at the default 0), then all three guests boot fine.

This reminds me of the case when Star introduced the non-executable stack for DXE, we turned it on in OVMF, and that killed the grub version shipped with an older Debian release:

https://www.mail-archive.com/edk2-devel@lists.01.org/msg02022.html

So ultimately we had to make the PCD dynamic, and make it default to "off" (see commit ab081a50e565, "OvmfPkg: PlatformPei: take no-exec DXE settings from the QEMU command line", 2015-09-15).

Thanks
Laszlo