OvmfPkg/VmgExitLib: Implement library support for VmgExitLib in OVMF

The base VmgExitLib library provides a default limited interface. As it does not provide full support, create an OVMF version of this library to begin the process of providing full support of SEV-ES within OVMF. SEV-ES support is only provided for X64 builds, so only OvmfPkgX64.dsc is updated to make use of the OvmfPkg version of the library. Cc: Jordan Justen <jordan.l.justen@intel.com> Cc: Laszlo Ersek <lersek@redhat.com> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com> Acked-by: Laszlo Ersek <lersek@redhat.com> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com> Regression-tested-by: Laszlo Ersek <lersek@redhat.com>
lersek · Aug 17, 2020 · 61bacc0 · 61bacc0
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diff --git a/OvmfPkg/Library/VmgExitLib/VmgExitLib.c b/OvmfPkg/Library/VmgExitLib/VmgExitLib.c
@@ -0,0 +1,159 @@
+/** @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;
+
+  //
+  // 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
+
+**/
+VOID
+EFIAPI
+VmgInit (
+  IN OUT GHCB                *Ghcb
+  )
+{
+  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
+
+**/
+VOID
+EFIAPI
+VmgDone (
+  IN OUT GHCB                *Ghcb
+  )
+{
+}
+
diff --git a/OvmfPkg/Library/VmgExitLib/VmgExitLib.inf b/OvmfPkg/Library/VmgExitLib/VmgExitLib.inf
@@ -0,0 +1,36 @@
+## @file
+#  VMGEXIT Support Library.
+#
+#  Copyright (C) 2020, Advanced Micro Devices, Inc. All rights reserved.<BR>
+#  SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+##
+
+[Defines]
+  INF_VERSION                    = 0x00010005
+  BASE_NAME                      = VmgExitLib
+  FILE_GUID                      = 0e923c25-13cd-430b-8714-ffe85652a97b
+  MODULE_TYPE                    = BASE
+  VERSION_STRING                 = 1.0
+  LIBRARY_CLASS                  = VmgExitLib
+
+#
+# The following information is for reference only and not required by the build tools.
+#
+#  VALID_ARCHITECTURES           = X64
+#
+
+[Sources.common]
+  VmgExitLib.c
+  VmgExitVcHandler.c
+
+[Packages]
+  MdePkg/MdePkg.dec
+  OvmfPkg/OvmfPkg.dec
+  UefiCpuPkg/UefiCpuPkg.dec
+
+[LibraryClasses]
+  BaseLib
+  BaseMemoryLib
+  DebugLib
+
diff --git a/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c b/OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c
@@ -0,0 +1,81 @@
+/** @file
+  X64 #VC Exception Handler functon.
+
+  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>
+
+/**
+  Handle a #VC exception.
+
+  Performs the necessary processing to handle a #VC exception.
+
+  @param[in, out]  ExceptionType  Pointer to an EFI_EXCEPTION_TYPE to be set
+                                  as value to use on error.
+  @param[in, out]  SystemContext  Pointer to EFI_SYSTEM_CONTEXT
+
+  @retval  EFI_SUCCESS            Exception handled
+  @retval  EFI_UNSUPPORTED        #VC not supported, (new) exception value to
+                                  propagate provided
+  @retval  EFI_PROTOCOL_ERROR     #VC handling failed, (new) exception value to
+                                  propagate provided
+
+**/
+EFI_STATUS
+EFIAPI
+VmgExitHandleVc (
+  IN OUT EFI_EXCEPTION_TYPE  *ExceptionType,
+  IN OUT EFI_SYSTEM_CONTEXT  SystemContext
+  )
+{
+  MSR_SEV_ES_GHCB_REGISTER  Msr;
+  EFI_SYSTEM_CONTEXT_X64    *Regs;
+  GHCB                      *Ghcb;
+  UINT64                    ExitCode, Status;
+  EFI_STATUS                VcRet;
+
+  VcRet = EFI_SUCCESS;
+
+  Msr.GhcbPhysicalAddress = AsmReadMsr64 (MSR_SEV_ES_GHCB);
+  ASSERT (Msr.GhcbInfo.Function == 0);
+  ASSERT (Msr.Ghcb != 0);
+
+  Regs = SystemContext.SystemContextX64;
+  Ghcb = Msr.Ghcb;
+
+  VmgInit (Ghcb);
+
+  ExitCode = Regs->ExceptionData;
+  switch (ExitCode) {
+  default:
+    Status = VmgExit (Ghcb, SVM_EXIT_UNSUPPORTED, ExitCode, 0);
+    if (Status == 0) {
+      Regs->ExceptionData = 0;
+      *ExceptionType = GP_EXCEPTION;
+    } else {
+      GHCB_EVENT_INJECTION  Event;
+
+      Event.Uint64 = Status;
+      if (Event.Elements.ErrorCodeValid != 0) {
+        Regs->ExceptionData = Event.Elements.ErrorCode;
+      } else {
+        Regs->ExceptionData = 0;
+      }
+
+      *ExceptionType = Event.Elements.Vector;
+    }
+
+    VcRet = EFI_PROTOCOL_ERROR;
+  }
+
+  VmgDone (Ghcb);
+
+  return VcRet;
+}
diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc
@@ -233,7 +233,7 @@
 
 [LibraryClasses.common]
   BaseCryptLib|CryptoPkg/Library/BaseCryptLib/BaseCryptLib.inf
-  VmgExitLib|UefiCpuPkg/Library/VmgExitLibNull/VmgExitLibNull.inf
+  VmgExitLib|OvmfPkg/Library/VmgExitLib/VmgExitLib.inf
 
 [LibraryClasses.common.SEC]
   TimerLib|OvmfPkg/Library/AcpiTimerLib/BaseRomAcpiTimerLib.inf