system76-edk2/OvmfPkg/Library/VmgExitLib/VmgExitLib.c

/** @file
  VMGEXIT Support Library.

  Copyright (C) 2020, Advanced Micro Devices, Inc. All rights reserved.<BR>
  SPDX-License-Identifier: BSD-2-Clause-Patent

**/

#include <Base.h>
#include <Uefi.h>
#include <Library/BaseMemoryLib.h>
#include <Library/VmgExitLib.h>
#include <Register/Amd/Msr.h>

/**
  Check for VMGEXIT error

  Check if the hypervisor has returned an error after completion of the VMGEXIT
  by examining the SwExitInfo1 field of the GHCB.

  @param[in]  Ghcb       A pointer to the GHCB

  @retval  0             VMGEXIT succeeded.
  @return                Exception number to be propagated, VMGEXIT processing
                         did not succeed.

**/
STATIC
UINT64
VmgExitErrorCheck (
  IN GHCB                *Ghcb
  )
{
  GHCB_EVENT_INJECTION  Event;
  GHCB_EXIT_INFO        ExitInfo;
  UINT64                Status;

  ExitInfo.Uint64 = Ghcb->SaveArea.SwExitInfo1;
  ASSERT ((ExitInfo.Elements.Lower32Bits == 0) ||
          (ExitInfo.Elements.Lower32Bits == 1));

  Status = 0;
  if (ExitInfo.Elements.Lower32Bits == 0) {
    return Status;
  }

  if (ExitInfo.Elements.Lower32Bits == 1) {
    ASSERT (Ghcb->SaveArea.SwExitInfo2 != 0);

    //
    // Check that the return event is valid
    //
    Event.Uint64 = Ghcb->SaveArea.SwExitInfo2;
    if (Event.Elements.Valid &&
        Event.Elements.Type == GHCB_EVENT_INJECTION_TYPE_EXCEPTION) {
      switch (Event.Elements.Vector) {
      case GP_EXCEPTION:
      case UD_EXCEPTION:
        //
        // Use returned event as return code
        //
        Status = Event.Uint64;
      }
    }
  }

  if (Status == 0) {
    GHCB_EVENT_INJECTION  GpEvent;

    GpEvent.Uint64 = 0;
    GpEvent.Elements.Vector = GP_EXCEPTION;
    GpEvent.Elements.Type   = GHCB_EVENT_INJECTION_TYPE_EXCEPTION;
    GpEvent.Elements.Valid  = 1;

    Status = GpEvent.Uint64;
  }

  return Status;
}

/**
  Perform VMGEXIT.

  Sets the necessary fields of the GHCB, invokes the VMGEXIT instruction and
  then handles the return actions.

  @param[in, out]  Ghcb       A pointer to the GHCB
  @param[in]       ExitCode   VMGEXIT code to be assigned to the SwExitCode
                              field of the GHCB.
  @param[in]       ExitInfo1  VMGEXIT information to be assigned to the
                              SwExitInfo1 field of the GHCB.
  @param[in]       ExitInfo2  VMGEXIT information to be assigned to the
                              SwExitInfo2 field of the GHCB.

  @retval  0                  VMGEXIT succeeded.
  @return                     Exception number to be propagated, VMGEXIT
                              processing did not succeed.

**/
UINT64
EFIAPI
VmgExit (
  IN OUT GHCB                *Ghcb,
  IN     UINT64              ExitCode,
  IN     UINT64              ExitInfo1,
  IN     UINT64              ExitInfo2
  )
{
  Ghcb->SaveArea.SwExitCode = ExitCode;
  Ghcb->SaveArea.SwExitInfo1 = ExitInfo1;
  Ghcb->SaveArea.SwExitInfo2 = ExitInfo2;

  VmgSetOffsetValid (Ghcb, GhcbSwExitCode);
  VmgSetOffsetValid (Ghcb, GhcbSwExitInfo1);
  VmgSetOffsetValid (Ghcb, GhcbSwExitInfo2);

  //
  // Guest memory is used for the guest-hypervisor communication, so fence
  // the invocation of the VMGEXIT instruction to ensure GHCB accesses are
  // synchronized properly.
  //
  MemoryFence ();
  AsmVmgExit ();
  MemoryFence ();

  return VmgExitErrorCheck (Ghcb);
}

/**
  Perform pre-VMGEXIT initialization/preparation.

  Performs the necessary steps in preparation for invoking VMGEXIT. Must be
  called before setting any fields within the GHCB.

  @param[in, out]  Ghcb            A pointer to the GHCB
  @param[in, out]  InterruptState  A pointer to hold the current interrupt
                                   state, used for restoring in VmgDone ()

**/
VOID
EFIAPI
VmgInit (
  IN OUT GHCB                *Ghcb,
  IN OUT BOOLEAN             *InterruptState
  )
{
  //
  // Be sure that an interrupt can't cause a #VC while the GHCB is
  // being used.
  //
  *InterruptState = GetInterruptState ();
  if (*InterruptState) {
    DisableInterrupts ();
  }

  SetMem (&Ghcb->SaveArea, sizeof (Ghcb->SaveArea), 0);
}

/**
  Perform post-VMGEXIT cleanup.

  Performs the necessary steps to cleanup after invoking VMGEXIT. Must be
  called after obtaining needed fields within the GHCB.

  @param[in, out]  Ghcb            A pointer to the GHCB
  @param[in]       InterruptState  An indicator to conditionally (re)enable
                                   interrupts

**/
VOID
EFIAPI
VmgDone (
  IN OUT GHCB                *Ghcb,
  IN     BOOLEAN             InterruptState
  )
{
  if (InterruptState) {
    EnableInterrupts ();
  }
}

/**
  Marks a field at the specified offset as valid in the GHCB.

  The ValidBitmap area represents the areas of the GHCB that have been marked
  valid. Set the bit in ValidBitmap for the input offset.

  @param[in, out] Ghcb    Pointer to the Guest-Hypervisor Communication Block
  @param[in]      Offset  Qword offset in the GHCB to mark valid

**/
VOID
EFIAPI
VmgSetOffsetValid (
  IN OUT GHCB                *Ghcb,
  IN     GHCB_REGISTER       Offset
  )
{
  UINT32  OffsetIndex;
  UINT32  OffsetBit;

  OffsetIndex = Offset / 8;
  OffsetBit   = Offset % 8;

  Ghcb->SaveArea.ValidBitmap[OffsetIndex] |= (1 << OffsetBit);
}

/**
  Checks if a specified offset is valid in the GHCB.

  The ValidBitmap area represents the areas of the GHCB that have been marked
  valid. Return whether the bit in the ValidBitmap is set for the input offset.

  @param[in]  Ghcb            A pointer to the GHCB
  @param[in]  Offset          Qword offset in the GHCB to mark valid

  @retval TRUE                Offset is marked valid in the GHCB
  @retval FALSE               Offset is not marked valid in the GHCB

**/
BOOLEAN
EFIAPI
VmgIsOffsetValid (
  IN GHCB                    *Ghcb,
  IN GHCB_REGISTER           Offset
  )
{
  UINT32  OffsetIndex;
  UINT32  OffsetBit;

  OffsetIndex = Offset / 8;
  OffsetBit   = Offset % 8;

  return ((Ghcb->SaveArea.ValidBitmap[OffsetIndex] & (1 << OffsetBit)) != 0);
}