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   This program and the accompanying materials are licensed and made available
  10   under the terms and conditions of the BSD License which accompanies this
  11   distribution.  The full text of the license may be found at
  12   http://opensource.org/licenses/bsd-license.php
  13
  14   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, WITHOUT
  15   WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  16
  17 **/
  18
  19 #include <Library/BaseLib.h>
  20 #include <Library/BaseMemoryLib.h>
  21 #include <Library/DebugLib.h>
  22 #include <Library/DxeServicesTableLib.h>
  23 #include <Library/MemEncryptSevLib.h>
  24 #include <Library/MemoryAllocationLib.h>
  25 #include <Library/PcdLib.h>
  26
  27 EFI_STATUS
  28 EFIAPI
  29 AmdSevDxeEntryPoint (
  30   IN EFI_HANDLE         ImageHandle,
  31   IN EFI_SYSTEM_TABLE   *SystemTable
  32   )
  33 {
  34   EFI_STATUS                       Status;
  35   EFI_GCD_MEMORY_SPACE_DESCRIPTOR  *AllDescMap;
  36   UINTN                            NumEntries;
  37   UINTN                            Index;
  38
  39   //
  40   // Do nothing when SEV is not enabled
  41   //
  42   if (!MemEncryptSevIsEnabled ()) {
  43     return EFI_UNSUPPORTED;
  44   }
  45
  46   //
  47   // Iterate through the GCD map and clear the C-bit from MMIO and NonExistent
  48   // memory space. The NonExistent memory space will be used for mapping the
  49   // MMIO space added later (eg PciRootBridge). By clearing both known MMIO and
  50   // NonExistent memory space can gurantee that current and furture MMIO adds
  51   // will have C-bit cleared.
  52   //
  53   Status = gDS->GetMemorySpaceMap (&NumEntries, &AllDescMap);
  54   if (!EFI_ERROR (Status)) {
  55     for (Index = 0; Index < NumEntries; Index++) {
  56       CONST EFI_GCD_MEMORY_SPACE_DESCRIPTOR *Desc;
  57
  58       Desc = &AllDescMap[Index];
  59       if (Desc->GcdMemoryType == EfiGcdMemoryTypeMemoryMappedIo ||
  60           Desc->GcdMemoryType == EfiGcdMemoryTypeNonExistent) {
  61         Status = MemEncryptSevClearPageEncMask (
  62                    0,
  63                    Desc->BaseAddress,
  64                    EFI_SIZE_TO_PAGES (Desc->Length),
  65                    FALSE
  66                    );
  67         ASSERT_EFI_ERROR (Status);
  68       }
  69     }
  70
  71     FreePool (AllDescMap);
  72   }
  73
  74   //
  75   // When SMM is enabled, clear the C-bit from SMM Saved State Area
  76   //
  77   // NOTES: The SavedStateArea address cleared here is before SMBASE
  78   // relocation. Currently, we do not clear the SavedStateArea address after
  79   // SMBASE is relocated due to the following reasons:
  80   //
  81   // 1) Guest BIOS never access the relocated SavedStateArea.
  82   //
  83   // 2) The C-bit works on page-aligned address, but the SavedStateArea
  84   // address is not a page-aligned. Theoretically, we could roundup the address
  85   // and clear the C-bit of aligned address but looking carefully we found
  86   // that some portion of the page contains code -- which will causes a bigger
  87   // issues for SEV guest. When SEV is enabled, all the code must be encrypted
  88   // otherwise hardware will cause trap.
  89   //
  90   // We restore the C-bit for this SMM Saved State Area after SMBASE relocation
  91   // is completed (See OvmfPkg/Library/SmmCpuFeaturesLib/SmmCpuFeaturesLib.c).
  92   //
  93   if (FeaturePcdGet (PcdSmmSmramRequire)) {
  94     UINTN MapPagesBase;
  95     UINTN MapPagesCount;
  96
  97     Status = MemEncryptSevLocateInitialSmramSaveStateMapPages (
  98                &MapPagesBase,
  99                &MapPagesCount
 100                );
 101     ASSERT_EFI_ERROR (Status);
 102
 103     //
 104     // Although these pages were set aside (i.e., allocated) by PlatformPei, we
 105     // could be after a warm reboot from the OS. Don't leak any stale OS data
 106     // to the hypervisor.
 107     //
 108     ZeroMem ((VOID *)MapPagesBase, EFI_PAGES_TO_SIZE (MapPagesCount));
 109
 110     Status = MemEncryptSevClearPageEncMask (
 111                0,             // Cr3BaseAddress -- use current CR3
 112                MapPagesBase,  // BaseAddress
 113                MapPagesCount, // NumPages
 114                TRUE           // Flush
 115                );
 116     if (EFI_ERROR (Status)) {
 117       DEBUG ((DEBUG_ERROR, "%a: MemEncryptSevClearPageEncMask(): %r\n",
 118         __FUNCTION__, Status));
 119       ASSERT (FALSE);
 120       CpuDeadLoop ();
 121     }
 122   }
 123
 124   return EFI_SUCCESS;
 125 }