OvmfPkg/AmdSevDxe/AmdSevDxe.c

   1 /** @file
   2
   3   AMD Sev Dxe driver. This driver is dispatched early in DXE, due to being list
   4   in APRIORI. It clears C-bit from MMIO and NonExistent Memory space when SEV
   5   is enabled.
   6
   7   Copyright (c) 2017, AMD Inc. All rights reserved.<BR>
   8
   9   SPDX-License-Identifier: BSD-2-Clause-Patent
  10
  11 **/
  12
  13 #include <Library/BaseLib.h>
  14 #include <Library/BaseMemoryLib.h>
  15 #include <Library/DebugLib.h>
  16 #include <Library/DxeServicesTableLib.h>
  17 #include <Library/MemEncryptSevLib.h>
  18 #include <Library/MemoryAllocationLib.h>
  19 #include <Library/PcdLib.h>
  20
  21 EFI_STATUS
  22 EFIAPI
  23 AmdSevDxeEntryPoint (
  24   IN EFI_HANDLE         ImageHandle,
  25   IN EFI_SYSTEM_TABLE   *SystemTable
  26   )
  27 {
  28   EFI_STATUS                       Status;
  29   EFI_GCD_MEMORY_SPACE_DESCRIPTOR  *AllDescMap;
  30   UINTN                            NumEntries;
  31   UINTN                            Index;
  32
  33   //
  34   // Do nothing when SEV is not enabled
  35   //
  36   if (!MemEncryptSevIsEnabled ()) {
  37     return EFI_UNSUPPORTED;
  38   }
  39
  40   //
  41   // Iterate through the GCD map and clear the C-bit from MMIO and NonExistent
  42   // memory space. The NonExistent memory space will be used for mapping the
  43   // MMIO space added later (eg PciRootBridge). By clearing both known MMIO and
  44   // NonExistent memory space can gurantee that current and furture MMIO adds
  45   // will have C-bit cleared.
  46   //
  47   Status = gDS->GetMemorySpaceMap (&NumEntries, &AllDescMap);
  48   if (!EFI_ERROR (Status)) {
  49     for (Index = 0; Index < NumEntries; Index++) {
  50       CONST EFI_GCD_MEMORY_SPACE_DESCRIPTOR *Desc;
  51
  52       Desc = &AllDescMap[Index];
  53       if (Desc->GcdMemoryType == EfiGcdMemoryTypeMemoryMappedIo ||
  54           Desc->GcdMemoryType == EfiGcdMemoryTypeNonExistent) {
  55         Status = MemEncryptSevClearPageEncMask (
  56                    0,
  57                    Desc->BaseAddress,
  58                    EFI_SIZE_TO_PAGES (Desc->Length),
  59                    FALSE
  60                    );
  61         ASSERT_EFI_ERROR (Status);
  62       }
  63     }
  64
  65     FreePool (AllDescMap);
  66   }
  67
  68   //
  69   // When SMM is enabled, clear the C-bit from SMM Saved State Area
  70   //
  71   // NOTES: The SavedStateArea address cleared here is before SMBASE
  72   // relocation. Currently, we do not clear the SavedStateArea address after
  73   // SMBASE is relocated due to the following reasons:
  74   //
  75   // 1) Guest BIOS never access the relocated SavedStateArea.
  76   //
  77   // 2) The C-bit works on page-aligned address, but the SavedStateArea
  78   // address is not a page-aligned. Theoretically, we could roundup the address
  79   // and clear the C-bit of aligned address but looking carefully we found
  80   // that some portion of the page contains code -- which will causes a bigger
  81   // issues for SEV guest. When SEV is enabled, all the code must be encrypted
  82   // otherwise hardware will cause trap.
  83   //
  84   // We restore the C-bit for this SMM Saved State Area after SMBASE relocation
  85   // is completed (See OvmfPkg/Library/SmmCpuFeaturesLib/SmmCpuFeaturesLib.c).
  86   //
  87   if (FeaturePcdGet (PcdSmmSmramRequire)) {
  88     UINTN MapPagesBase;
  89     UINTN MapPagesCount;
  90
  91     Status = MemEncryptSevLocateInitialSmramSaveStateMapPages (
  92                &MapPagesBase,
  93                &MapPagesCount
  94                );
  95     ASSERT_EFI_ERROR (Status);
  96
  97     //
  98     // Although these pages were set aside (i.e., allocated) by PlatformPei, we
  99     // could be after a warm reboot from the OS. Don't leak any stale OS data
 100     // to the hypervisor.
 101     //
 102     ZeroMem ((VOID *)MapPagesBase, EFI_PAGES_TO_SIZE (MapPagesCount));
 103
 104     Status = MemEncryptSevClearPageEncMask (
 105                0,             // Cr3BaseAddress -- use current CR3
 106                MapPagesBase,  // BaseAddress
 107                MapPagesCount, // NumPages
 108                TRUE           // Flush
 109                );
 110     if (EFI_ERROR (Status)) {
 111       DEBUG ((DEBUG_ERROR, "%a: MemEncryptSevClearPageEncMask(): %r\n",
 112         __FUNCTION__, Status));
 113       ASSERT (FALSE);
 114       CpuDeadLoop ();
 115     }
 116   }
 117
 118   return EFI_SUCCESS;
 119 }