OvmfPkg/AmdSev: Expose the Sev Secret area using a configuration table

Now that the secret area is protected by a boot time HOB, extract its
location details into a configuration table referenced by
gSevLaunchSecretGuid so the boot loader or OS can locate it before a
call to ExitBootServices().

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3077
Signed-off-by: James Bottomley <jejb@linux.ibm.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20201130202819.3910-7-jejb@linux.ibm.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
[lersek@redhat.com: fix indentation of InstallConfigurationTable() args]

OvmfPkg/AmdSev/AmdSevX64.dsc

@@ -778,6 +778,7 @@
       gEfiShellPkgTokenSpaceGuid.PcdShellLibAutoInitialize|FALSE
   }
 !endif
+  OvmfPkg/AmdSev/SecretDxe/SecretDxe.inf
   OvmfPkg/AmdSev/Grub/Grub.inf
 !if $(BUILD_SHELL) == TRUE
   ShellPkg/Application/Shell/Shell.inf {

OvmfPkg/AmdSev/AmdSevX64.fdf

@@ -269,6 +269,7 @@ INF  MdeModulePkg/Universal/Disk/UdfDxe/UdfDxe.inf
 !if $(TOOL_CHAIN_TAG) != "XCODE5" && $(BUILD_SHELL) == TRUE
 INF  OvmfPkg/LinuxInitrdDynamicShellCommand/LinuxInitrdDynamicShellCommand.inf
 !endif
+INF OvmfPkg/AmdSev/SecretDxe/SecretDxe.inf
 INF  OvmfPkg/AmdSev/Grub/Grub.inf
 !if $(BUILD_SHELL) == TRUE
 INF  ShellPkg/Application/Shell/Shell.inf

OvmfPkg/AmdSev/SecretDxe/SecretDxe.c

@@ -0,0 +1,27 @@
+/** @file
+  SEV Secret configuration table constructor
+
+  Copyright (C) 2020 James Bottomley, IBM Corporation.
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+**/
+#include <PiDxe.h>
+#include <Library/UefiBootServicesTableLib.h>
+#include <Guid/SevLaunchSecret.h>
+
+STATIC SEV_LAUNCH_SECRET_LOCATION mSecretDxeTable = {
+  FixedPcdGet32 (PcdSevLaunchSecretBase),
+  FixedPcdGet32 (PcdSevLaunchSecretSize),
+};
+
+EFI_STATUS
+EFIAPI
+InitializeSecretDxe(
+  IN EFI_HANDLE           ImageHandle,
+  IN EFI_SYSTEM_TABLE     *SystemTable
+  )
+{
+  return gBS->InstallConfigurationTable (
+                &gSevLaunchSecretGuid,
+                &mSecretDxeTable
+                );
+}

OvmfPkg/AmdSev/SecretDxe/SecretDxe.inf

@@ -0,0 +1,37 @@
+## @file
+#  Sev Secret configuration Table installer
+#
+#  Copyright (C) 2020 James Bottomley, IBM Corporation.
+#
+#  SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+##
+
+[Defines]
+  INF_VERSION                    = 0x00010005
+  BASE_NAME                      = SecretDxe
+  FILE_GUID                      = 6e2b9619-8810-4e9d-a177-d432bb9abeda
+  MODULE_TYPE                    = DXE_DRIVER
+  VERSION_STRING                 = 1.0
+  ENTRY_POINT                    = InitializeSecretDxe
+
+[Sources]
+  SecretDxe.c
+
+[Packages]
+  OvmfPkg/OvmfPkg.dec
+  MdePkg/MdePkg.dec
+
+[LibraryClasses]
+  UefiBootServicesTableLib
+  UefiDriverEntryPoint
+
+[Guids]
+  gSevLaunchSecretGuid
+
+[FixedPcd]
+  gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretBase
+  gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretSize
+
+[Depex]
+  TRUE

OvmfPkg/Include/Guid/SevLaunchSecret.h

@@ -0,0 +1,28 @@
+ /** @file
+   UEFI Configuration Table for exposing the SEV Launch Secret location to UEFI
+   applications (boot loaders).
+
+   Copyright (C) 2020 James Bottomley, IBM Corporation.
+   SPDX-License-Identifier: BSD-2-Clause-Patent
+ **/
+
+#ifndef SEV_LAUNCH_SECRET_H_
+#define SEV_LAUNCH_SECRET_H_
+
+#include <Uefi/UefiBaseType.h>
+
+#define SEV_LAUNCH_SECRET_GUID                          \
+  { 0xadf956ad,                                         \
+    0xe98c,                                             \
+    0x484c,                                             \
+    { 0xae, 0x11, 0xb5, 0x1c, 0x7d, 0x33, 0x64, 0x47 }, \
+  }
+
+typedef struct {
+  UINT32 Base;
+  UINT32 Size;
+} SEV_LAUNCH_SECRET_LOCATION;
+
+extern EFI_GUID gSevLaunchSecretGuid;
+
+#endif // SEV_LAUNCH_SECRET_H_

OvmfPkg/OvmfPkg.dec

@@ -117,6 +117,7 @@
   gLinuxEfiInitrdMediaGuid              = {0x5568e427, 0x68fc, 0x4f3d, {0xac, 0x74, 0xca, 0x55, 0x52, 0x31, 0xcc, 0x68}}
   gQemuKernelLoaderFsMediaGuid          = {0x1428f772, 0xb64a, 0x441e, {0xb8, 0xc3, 0x9e, 0xbd, 0xd7, 0xf8, 0x93, 0xc7}}
   gGrubFileGuid                         = {0xb5ae312c, 0xbc8a, 0x43b1, {0x9c, 0x62, 0xeb, 0xb8, 0x26, 0xdd, 0x5d, 0x07}}
+  gSevLaunchSecretGuid                  = {0xadf956ad, 0xe98c, 0x484c, {0xae, 0x11, 0xb5, 0x1c, 0x7d, 0x33, 0x64, 0x47}}
 
 [Ppis]
   # PPI whose presence in the PPI database signals that the TPM base address