Re: [PATCH 1/2] ArmVirtPkg/HighMemDxe: use CPU arch protocol to apply memprotect policy

[Laszlo Ersek <lersek@redhat.com>]

On 03/21/17 10:23, Ard Biesheuvel wrote:
> Instead of invoking gDS->SetMemorySpaceAttributes to set the EFI_MEMORY_XP
> attribute on newly added regions, which is guaranteed to fail if the same
> attribute was not declared as a capability of the region when it as added,
> invoke the CPU arch protocol directly to set the EFI_MEMORY_XP attribute
> if our memory protection policy demands it.
> 
> Reported-by: Michael Zimmermann <sigmaepsilon92@gmail.com>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  ArmVirtPkg/HighMemDxe/HighMemDxe.c   | 31 +++++++++++++++-----
>  ArmVirtPkg/HighMemDxe/HighMemDxe.inf |  1 +
>  2 files changed, 25 insertions(+), 7 deletions(-)
> 
> diff --git a/ArmVirtPkg/HighMemDxe/HighMemDxe.c b/ArmVirtPkg/HighMemDxe/HighMemDxe.c
> index f70978f6414f..4e41120deff3 100644
> --- a/ArmVirtPkg/HighMemDxe/HighMemDxe.c
> +++ b/ArmVirtPkg/HighMemDxe/HighMemDxe.c
> @@ -20,6 +20,7 @@
>  #include <Library/PcdLib.h>
>  #include <Library/UefiBootServicesTableLib.h>
>  
> +#include <Protocol/Cpu.h>
>  #include <Protocol/FdtClient.h>
>  
>  EFI_STATUS
> @@ -30,6 +31,7 @@ InitializeHighMemDxe (
>    )
>  {
>    FDT_CLIENT_PROTOCOL   *FdtClient;
> +  EFI_CPU_ARCH_PROTOCOL *Cpu;
>    EFI_STATUS            Status, FindNodeStatus;
>    INT32                 Node;
>    CONST UINT32          *Reg;
> @@ -43,6 +45,10 @@ InitializeHighMemDxe (
>                    (VOID **)&FdtClient);
>    ASSERT_EFI_ERROR (Status);
>  
> +  Status = gBS->LocateProtocol (&gEfiCpuArchProtocolGuid, NULL,
> +                  (VOID **)&Cpu);
> +  ASSERT_EFI_ERROR (Status);
> +
>    //
>    // Check for memory node and add the memory spaces except the lowest one
>    //
> @@ -78,13 +84,24 @@ InitializeHighMemDxe (
>            continue;
>          }
>  
> +        Status = gDS->SetMemorySpaceAttributes (CurBase, CurSize,
> +                        EFI_MEMORY_WB);
> +        if (EFI_ERROR (Status)) {
> +          DEBUG ((DEBUG_WARN,
> +            "%a: gDS->SetMemorySpaceAttributes() failed on region 0x%lx - 0x%lx (%r)\n",
> +            __FUNCTION__, CurBase, CurBase + CurSize - 1, Status));
> +        }
> +
> +        //
> +        // Due to the ambiguous nature of the RO/XP GCD memory space attributes,
> +        // it is impossible to add a memory space with the XP attribute in a way
> +        // that does not result in the XP attribute being set on *all* UEFI
> +        // memory map entries that are carved from it, including code regions
> +        // that require executable permissions.
>          //
> -        // Take care not to strip any permission attributes that will have been
> -        // set by DxeCore on the region we just added if a strict permission
> -        // policy is in effect for EfiConventionalMemory regions.
> -        // Unfortunately, we cannot interrogate the GCD memory space map for
> -        // those permissions, since they are not recorded there (for historical
> -        // reasons), so check the policy directly.
> +        // So instead, we never set the RO/XP attributes in the GCD memory space
> +        // capabilities or attribute fields, and apply any protections directly
> +        // on the page table mappings by going through the cpu arch protocol.
>          //
>          Attributes = EFI_MEMORY_WB;
>          if ((PcdGet64 (PcdDxeNxMemoryProtectionPolicy) &
> @@ -92,7 +109,7 @@ InitializeHighMemDxe (
>            Attributes |= EFI_MEMORY_XP;
>          }
>  
> -        Status = gDS->SetMemorySpaceAttributes (CurBase, CurSize, Attributes);
> +        Status = Cpu->SetMemoryAttributes (Cpu, CurBase, CurSize, Attributes);
>  
>          if (EFI_ERROR (Status)) {
>            DEBUG ((EFI_D_ERROR,
> diff --git a/ArmVirtPkg/HighMemDxe/HighMemDxe.inf b/ArmVirtPkg/HighMemDxe/HighMemDxe.inf
> index 89c743ebe058..ac1761974f52 100644
> --- a/ArmVirtPkg/HighMemDxe/HighMemDxe.inf
> +++ b/ArmVirtPkg/HighMemDxe/HighMemDxe.inf
> @@ -41,6 +41,7 @@ [LibraryClasses]
>    UefiDriverEntryPoint
>  
>  [Protocols]
> +  gEfiCpuArchProtocolGuid                 ## CONSUMES
>    gFdtClientProtocolGuid                  ## CONSUMES
>  
>  [Pcd]
> 

gEfiCpuArchProtocolGuid is already part of the DEPEX, so:

Reviewed-by: Laszlo Ersek <lersek@redhat.com>