OvmfPkg/Library/VmgExitLib/SecVmgExitVcHandler.c

   1 /** @file
   2   X64 #VC Exception Handler functon.
   3
   4   Copyright (C) 2020, Advanced Micro Devices, Inc. All rights reserved.<BR>
   5   SPDX-License-Identifier: BSD-2-Clause-Patent
   6
   7 **/
   8
   9 #include <Base.h>
  10 #include <Uefi.h>
  11 #include <Library/BaseMemoryLib.h>
  12 #include <Library/MemEncryptSevLib.h>
  13 #include <Library/VmgExitLib.h>
  14 #include <Register/Amd/Msr.h>
  15
  16 #include "VmgExitVcHandler.h"
  17
  18 /**
  19   Handle a #VC exception.
  20
  21   Performs the necessary processing to handle a #VC exception.
  22
  23   @param[in, out]  ExceptionType  Pointer to an EFI_EXCEPTION_TYPE to be set
  24                                   as value to use on error.
  25   @param[in, out]  SystemContext  Pointer to EFI_SYSTEM_CONTEXT
  26
  27   @retval  EFI_SUCCESS            Exception handled
  28   @retval  EFI_UNSUPPORTED        #VC not supported, (new) exception value to
  29                                   propagate provided
  30   @retval  EFI_PROTOCOL_ERROR     #VC handling failed, (new) exception value to
  31                                   propagate provided
  32
  33 **/
  34 EFI_STATUS
  35 EFIAPI
  36 VmgExitHandleVc (
  37   IN OUT EFI_EXCEPTION_TYPE  *ExceptionType,
  38   IN OUT EFI_SYSTEM_CONTEXT  SystemContext
  39   )
  40 {
  41   MSR_SEV_ES_GHCB_REGISTER  Msr;
  42   GHCB                      *Ghcb;
  43   GHCB                      *GhcbBackup;
  44   EFI_STATUS                VcRet;
  45   BOOLEAN                   InterruptState;
  46   SEV_ES_PER_CPU_DATA       *SevEsData;
  47
  48   InterruptState = GetInterruptState ();
  49   if (InterruptState) {
  50     DisableInterrupts ();
  51   }
  52
  53   Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
  54   ASSERT (Msr.GhcbInfo.Function == 0);
  55   ASSERT (Msr.Ghcb != 0);
  56
  57   Ghcb       = Msr.Ghcb;
  58   GhcbBackup = NULL;
  59
  60   SevEsData = (SEV_ES_PER_CPU_DATA *)(Ghcb + 1);
  61   SevEsData->VcCount++;
  62
  63   //
  64   // Check for maximum SEC #VC nesting.
  65   //
  66   if (SevEsData->VcCount > VMGEXIT_MAXIMUM_VC_COUNT) {
  67     VmgExitIssueAssert (SevEsData);
  68   } else if (SevEsData->VcCount > 1) {
  69     UINTN  GhcbBackupSize;
  70
  71     //
  72     // Be sure that the proper amount of pages are allocated
  73     //
  74     GhcbBackupSize = (VMGEXIT_MAXIMUM_VC_COUNT - 1) * sizeof (*Ghcb);
  75     if (GhcbBackupSize > FixedPcdGet32 (PcdOvmfSecGhcbBackupSize)) {
  76       //
  77       // Not enough SEC backup pages allocated.
  78       //
  79       VmgExitIssueAssert (SevEsData);
  80     }
  81
  82     //
  83     // Save the active GHCB to a backup page.
  84     //   To access the correct backup page, increment the backup page pointer
  85     //   based on the current VcCount.
  86     //
  87     GhcbBackup  = (GHCB *)FixedPcdGet32 (PcdOvmfSecGhcbBackupBase);
  88     GhcbBackup += (SevEsData->VcCount - 2);
  89
  90     CopyMem (GhcbBackup, Ghcb, sizeof (*Ghcb));
  91   }
  92
  93   VcRet = InternalVmgExitHandleVc (Ghcb, ExceptionType, SystemContext);
  94
  95   if (GhcbBackup != NULL) {
  96     //
  97     // Restore the active GHCB from the backup page.
  98     //
  99     CopyMem (Ghcb, GhcbBackup, sizeof (*Ghcb));
 100   }
 101
 102   SevEsData->VcCount--;
 103
 104   if (InterruptState) {
 105     EnableInterrupts ();
 106   }
 107
 108   return VcRet;
 109 }