HighMemDxe.c

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#include <Library/BaseLib.h>
#include <Library/DebugLib.h>
#include <Library/DxeServicesTableLib.h>
#include <Library/PcdLib.h>
#include <Library/UefiBootServicesTableLib.h>
 
#include <Protocol/Cpu.h>
#include <Protocol/FdtClient.h>
 
EFI_STATUS
EFIAPI
InitializeHighMemDxe (
  IN EFI_HANDLE        ImageHandle,
  IN EFI_SYSTEM_TABLE  *SystemTable
  )
{
  FDT_CLIENT_PROTOCOL              *FdtClient;
  EFI_CPU_ARCH_PROTOCOL            *Cpu;
  EFI_STATUS                       Status, FindNodeStatus;
  INT32                            Node;
  CONST UINT32                     *Reg;
  UINT32                           RegSize;
  UINTN                            AddressCells, SizeCells;
  UINT64                           CurBase;
  UINT64                           CurSize;
  UINT64                           Attributes;
  EFI_GCD_MEMORY_SPACE_DESCRIPTOR  GcdDescriptor;
 
  Status = gBS->LocateProtocol (
                  &gFdtClientProtocolGuid,
                  NULL,
                  (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
  //
  for (FindNodeStatus = FdtClient->FindMemoryNodeReg (
                                     FdtClient,
                                     &Node,
                                     (CONST VOID **)&Reg,
                                     &AddressCells,
                                     &SizeCells,
                                     &RegSize
                                     );
       !EFI_ERROR (FindNodeStatus);
       FindNodeStatus = FdtClient->FindNextMemoryNodeReg (
                                     FdtClient,
                                     Node,
                                     &Node,
                                     (CONST VOID **)&Reg,
                                     &AddressCells,
                                     &SizeCells,
                                     &RegSize
                                     ))
  {
    ASSERT (AddressCells <= 2);
    ASSERT (SizeCells <= 2);
 
    while (RegSize > 0) {
      CurBase = SwapBytes32 (*Reg++);
      if (AddressCells > 1) {
        CurBase = (CurBase << 32) | SwapBytes32 (*Reg++);
      }
 
      CurSize = SwapBytes32 (*Reg++);
      if (SizeCells > 1) {
        CurSize = (CurSize << 32) | SwapBytes32 (*Reg++);
      }
 
      RegSize -= (AddressCells + SizeCells) * sizeof (UINT32);
 
      Status = gDS->GetMemorySpaceDescriptor (CurBase, &GcdDescriptor);
      if (EFI_ERROR (Status)) {
        DEBUG ((
          DEBUG_WARN,
          "%a: Region 0x%lx - 0x%lx not found in the GCD memory space map\n",
          __func__,
          CurBase,
          CurBase + CurSize - 1
          ));
        continue;
      }
 
      if (GcdDescriptor.GcdMemoryType == EfiGcdMemoryTypeNonExistent) {
        Status = gDS->AddMemorySpace (
                        EfiGcdMemoryTypeSystemMemory,
                        CurBase,
                        CurSize,
                        EFI_MEMORY_WB
                        );
 
        if (EFI_ERROR (Status)) {
          DEBUG ((
            DEBUG_ERROR,
            "%a: Failed to add System RAM @ 0x%lx - 0x%lx (%r)\n",
            __func__,
            CurBase,
            CurBase + CurSize - 1,
            Status
            ));
          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",
            __func__,
            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.
        //
        // 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) &
             (1U << (UINT32)EfiConventionalMemory)) != 0)
        {
          Attributes |= EFI_MEMORY_XP;
        }
 
        Status = Cpu->SetMemoryAttributes (Cpu, CurBase, CurSize, Attributes);
 
        if (EFI_ERROR (Status)) {
          DEBUG ((
            DEBUG_ERROR,
            "%a: Failed to set System RAM @ 0x%lx - 0x%lx attribute (%r)\n",
            __func__,
            CurBase,
            CurBase + CurSize - 1,
            Status
            ));
        } else {
          DEBUG ((
            DEBUG_INFO,
            "%a: Add System RAM @ 0x%lx - 0x%lx\n",
            __func__,
            CurBase,
            CurBase + CurSize - 1
            ));
        }
      }
    }
  }
 
  return EFI_SUCCESS;
}