OvmfPkg/VirtHstiDxe: add code flash check

Detects qemu config issue: code pflash is writable.
Checked for both PC and Q35.

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Konstantin Kostiuk <kkostiuk@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Jiewen Yao <Jiewen.yao@intel.com>

OvmfPkg/VirtHstiDxe/QemuCommon.c

@@ -0,0 +1,36 @@
+/** @file
+
+SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#include <Library/BaseLib.h>
+#include <Library/DebugLib.h>
+
+#include "VirtHstiDxe.h"
+
+VOID
+VirtHstiQemuCommonInit (
+  VIRT_ADAPTER_INFO_PLATFORM_SECURITY  *VirtHsti
+  )
+{
+  VirtHstiSetSupported (VirtHsti, 0, VIRT_HSTI_BYTE0_READONLY_CODE_FLASH);
+}
+
+VOID
+VirtHstiQemuCommonVerify (
+  VOID
+  )
+{
+  CHAR16  *ErrorMsg;
+
+  switch (VirtHstiQemuFirmwareFlashCheck (PcdGet32 (PcdBfvBase))) {
+    case QEMU_FIRMWARE_FLASH_WRITABLE:
+      ErrorMsg = L"qemu code pflash is writable";
+      break;
+    default:
+      ErrorMsg = NULL;
+  }
+
+  VirtHstiTestResult (ErrorMsg, 0, VIRT_HSTI_BYTE0_READONLY_CODE_FLASH);
+}