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/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_