diff -Naur VirtualBox-6.1.18/src/VBox/Devices/EFI/Firmware/VBoxPkg/VBoxFsDxe/fsw_efi.c VirtualBox-6.1.18-p/src/VBox/Devices/EFI/Firmware/VBoxPkg/VBoxFsDxe/fsw_efi.c
--- VirtualBox-6.1.18/src/VBox/Devices/EFI/Firmware/VBoxPkg/VBoxFsDxe/fsw_efi.c	2021-01-07 16:39:14.000000000 +0100
+++ VirtualBox-6.1.18-p/src/VBox/Devices/EFI/Firmware/VBoxPkg/VBoxFsDxe/fsw_efi.c	2021-01-30 02:19:42.121968017 +0100
@@ -384,6 +384,181 @@
 }
 #endif
 
+#if defined(VBOX)
+//
+// Extract INT32 from char array
+//
+#define UNPACK_INT32(a) (INT32)( (((UINT8 *) a)[0] <<  0) |    \
+                                 (((UINT8 *) a)[1] <<  8) |    \
+                                 (((UINT8 *) a)[2] << 16) |    \
+                                 (((UINT8 *) a)[3] << 24) )
+
+/**
+  Test for presence of one or more El Torito EFI boot entries.
+
+  @param[in]  BlockIo             BlockIo interface.
+  @param[in]  DiskIo              DiskIo interface.
+
+  @retval EFI_SUCCESS             An El Torito EFI boot entry was found.
+  @retval EFI_NOT_FOUND           An El Torito EFI boot entry was not found.
+  @retval other                   Failed to perform disk I/O.
+
+**/
+EFI_STATUS
+FindElToritoBootEntry (
+  IN EFI_BLOCK_IO_PROTOCOL  *BlockIo,
+  IN EFI_DISK_IO_PROTOCOL   *DiskIo
+  )
+{
+  EFI_STATUS                   Status;
+  EFI_BLOCK_IO_MEDIA           *Media;
+  CDROM_VOLUME_DESCRIPTOR      *VolDescriptor;
+  ELTORITO_CATALOG             *Catalog;
+  UINT64                       VolDescriptorOffset;
+  UINT32                       Lba2KB;
+  UINTN                        Check;
+  UINT16                       *CheckBuffer;
+  UINTN                        Index;
+  UINTN                        InEfiSection;
+  UINTN                        MaxIndex;
+  EFI_STATUS                   Found;
+
+  Found         = EFI_NOT_FOUND;
+  Media         = BlockIo->Media;
+
+  //
+  // CD_ROM has the fixed block size as 2048 bytes (SIZE_2KB)
+  //
+
+  // If the ISO image has been copied onto a different storage media
+  // then the block size might be different (eg: USB).
+  // Ensure 2048 (SIZE_2KB) is a multiple of block size
+  if (((SIZE_2KB % Media->BlockSize) != 0) || (Media->BlockSize > SIZE_2KB)) {
+    return EFI_NOT_FOUND;
+  }
+
+  VolDescriptor = AllocatePool ((UINTN)SIZE_2KB);
+
+  if (VolDescriptor == NULL) {
+    return EFI_NOT_FOUND;
+  }
+
+  Catalog = (ELTORITO_CATALOG *) VolDescriptor;
+
+  //
+  // Loop: handle one volume descriptor per time
+  //       The ISO-9660 volume descriptor starts at 32k on the media
+  //
+  for (VolDescriptorOffset = SIZE_32KB;
+       VolDescriptorOffset <= MultU64x32 (Media->LastBlock, Media->BlockSize);
+       VolDescriptorOffset += SIZE_2KB) {
+    Status = DiskIo->ReadDisk (
+                       DiskIo,
+                       Media->MediaId,
+                       VolDescriptorOffset,
+                       SIZE_2KB,
+                       VolDescriptor
+                       );
+    if (EFI_ERROR (Status)) {
+      Found = Status;
+      break;
+    }
+    //
+    // Check for valid volume descriptor signature
+    //
+    if (VolDescriptor->Unknown.Type == CDVOL_TYPE_END ||
+        CompareMem (VolDescriptor->Unknown.Id, CDVOL_ID, sizeof (VolDescriptor->Unknown.Id)) != 0
+        ) {
+      //
+      // end of Volume descriptor list
+      //
+      break;
+    }
+    //
+    // Is it an El Torito volume descriptor?
+    //
+    if (CompareMem (VolDescriptor->BootRecordVolume.SystemId, CDVOL_ELTORITO_ID, sizeof (CDVOL_ELTORITO_ID) - 1) != 0) {
+      continue;
+    }
+    //
+    // Read in the boot El Torito boot catalog
+    // The LBA unit used by El Torito boot catalog is 2KB unit
+    //
+    Lba2KB = UNPACK_INT32 (VolDescriptor->BootRecordVolume.EltCatalog);
+    // Ensure the LBA (in 2KB unit) fits into our media
+    if (Lba2KB * (SIZE_2KB / Media->BlockSize) > Media->LastBlock) {
+      continue;
+    }
+
+    Status = DiskIo->ReadDisk (
+                       DiskIo,
+                       Media->MediaId,
+                       MultU64x32 (Lba2KB, SIZE_2KB),
+                       SIZE_2KB,
+                       Catalog
+                       );
+    if (EFI_ERROR (Status)) {
+      DEBUG ((EFI_D_ERROR, "EltCheckDevice: error reading catalog %r\n", Status));
+      continue;
+    }
+    //
+    // We don't care too much about the Catalog header's contents, but we do want
+    // to make sure it looks like a Catalog header
+    //
+    if (Catalog->Catalog.Indicator != ELTORITO_ID_CATALOG || Catalog->Catalog.Id55AA != 0xAA55) {
+      DEBUG ((EFI_D_ERROR, "EltCheckBootCatalog: El Torito boot catalog header IDs not correct\n"));
+      continue;
+    }
+
+    Check       = 0;
+    CheckBuffer = (UINT16 *) Catalog;
+    for (Index = 0; Index < sizeof (ELTORITO_CATALOG) / sizeof (UINT16); Index += 1) {
+      Check += CheckBuffer[Index];
+    }
+
+    if ((Check & 0xFFFF) != 0) {
+      DEBUG ((EFI_D_ERROR, "EltCheckBootCatalog: El Torito boot catalog header checksum failed\n"));
+      continue;
+    }
+
+    InEfiSection = 0;
+
+    //
+    // Here we limit the scan to a single media block. In theory
+    // an El Torito catalog can extend beyond that; in practice
+    // that's unlikely.
+    //
+    MaxIndex = Media->BlockSize / sizeof (ELTORITO_CATALOG);
+    for (Index = 1; Index < MaxIndex; Index += 1) {
+      //
+      // Next entry
+      //
+      Catalog += 1;
+
+      //
+      // Check this entry
+      //
+      if (Catalog->Section.Indicator == ELTORITO_ID_SECTION_HEADER ||
+          Catalog->Section.Indicator == ELTORITO_ID_SECTION_HEADER_FINAL) {
+        InEfiSection = Catalog->Section.PlatformId == 0xEF;
+        continue;
+      }
+      if (InEfiSection &&
+          Catalog->Boot.Indicator == ELTORITO_ID_SECTION_BOOTABLE &&
+          Catalog->Boot.MediaType == ELTORITO_NO_EMULATION &&
+          Catalog->Boot.Lba != 0) {
+        Found = EFI_SUCCESS;
+        break;
+      }
+    }
+  }
+
+  FreePool (VolDescriptor);
+
+  return Found;
+}
+#endif
+
 static EFI_STATUS fsw_efi_ReMount(IN FSW_VOLUME_DATA *pVolume,
                                        IN EFI_HANDLE      ControllerHandle,
                                        EFI_DISK_IO        *pDiskIo,
@@ -411,6 +586,20 @@
         if (!EFI_ERROR(Status))
             Status = EFI_UNSUPPORTED;
         else
+            Status = EFI_SUCCESS;
+    }
+#endif
+#if defined(VBOX)
+    /*
+     * Don't give the iso9660 filesystem driver a chance to claim a volume which contains
+     * an El Torito EFI boot entry or we lose the capability to boot from that entry.
+     */
+    if (!EFI_ERROR(Status))
+    {
+        Status = FindElToritoBootEntry(pBlockIo, pDiskIo);
+        if (!EFI_ERROR(Status))
+            Status = EFI_UNSUPPORTED;
+        else
             Status = EFI_SUCCESS;
     }
 #endif