From 02916fa2f7b92b060bbdc70b2083d0fcf6139624 Mon Sep 17 00:00:00 2001
From: Dov Murik <dovmurik@linux.ibm.com>
Date: Thu, 15 Dec 2022 13:11:51 +0000
Subject: [PATCH] OvmfPkg/AmdSev/SecretDxe: Allocate secret location as
 EfiACPIReclaimMemory

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4186

Commit 079a58276b98 ("OvmfPkg/AmdSev/SecretPei: Mark SEV launch secret
area as reserved") marked the launch secret area itself (1 page) as
reserved so the guest OS can use it during the lifetime of the OS.
However, the address and size of the secret area held in the
CONFIDENTIAL_COMPUTING_SECRET_LOCATION struct are declared as STATIC in
OVMF (in AmdSev/SecretDxe); therefore there's no guarantee that it will
not be written over by OS data.

Fix this by allocating the memory for the
CONFIDENTIAL_COMPUTING_SECRET_LOCATION struct with the
EfiACPIReclaimMemory memory type to ensure the guest OS will not reuse
this memory.

Fixes: 079a58276b98 ("OvmfPkg/AmdSev/SecretPei: Mark SEV launch secret ...")
Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
---
 OvmfPkg/AmdSev/SecretDxe/SecretDxe.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/OvmfPkg/AmdSev/SecretDxe/SecretDxe.c b/OvmfPkg/AmdSev/SecretDxe/SecretDxe.c
index 934ad20..c851176 100644
--- a/OvmfPkg/AmdSev/SecretDxe/SecretDxe.c
+++ b/OvmfPkg/AmdSev/SecretDxe/SecretDxe.c
@@ -8,11 +8,6 @@
 #include <Library/UefiBootServicesTableLib.h>
 #include <Guid/ConfidentialComputingSecret.h>
 
-STATIC CONFIDENTIAL_COMPUTING_SECRET_LOCATION mSecretDxeTable = {
-  FixedPcdGet32 (PcdSevLaunchSecretBase),
-  FixedPcdGet32 (PcdSevLaunchSecretSize),
-};
-
 EFI_STATUS
 EFIAPI
 InitializeSecretDxe(
@@ -20,8 +15,23 @@ InitializeSecretDxe(
   IN EFI_SYSTEM_TABLE     *SystemTable
   )
 {
+  EFI_STATUS                              Status;
+  CONFIDENTIAL_COMPUTING_SECRET_LOCATION  *SecretDxeTable;
+
+  Status = gBS->AllocatePool (
+                  EfiACPIReclaimMemory,
+                  sizeof (CONFIDENTIAL_COMPUTING_SECRET_LOCATION),
+                  (VOID **)&SecretDxeTable
+                  );
+  if (EFI_ERROR (Status)) {
+    return Status;
+  }
+
+  SecretDxeTable->Base = FixedPcdGet32 (PcdSevLaunchSecretBase);
+  SecretDxeTable->Size = FixedPcdGet32 (PcdSevLaunchSecretSize);
+
   return gBS->InstallConfigurationTable (
                 &gConfidentialComputingSecretGuid,
-                &mSecretDxeTable
+                SecretDxeTable
                 );
 }
-- 
2.41.0