Re: [PATCH V3 2/3] MdeModulePkg/PartitionDxe: Skip the MBR that add for CD-ROM

["Ni, Ray" <ray.ni@intel.com>]

Reviewed-by: Ray Ni <ray.ni@intel.com>

> -----Original Message-----
> From: Gao, Zhichao <zhichao.gao@intel.com>
> Sent: Tuesday, July 14, 2020 9:23 AM
> To: devel@edk2.groups.io
> Cc: Wu, Hao A <hao.a.wu@intel.com>; Ni, Ray <ray.ni@intel.com>
> Subject: [PATCH V3 2/3] MdeModulePkg/PartitionDxe: Skip the MBR that add
> for CD-ROM
> 
> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2823
> 
> Refer to
> http://manpages.ubuntu.com/manpages/bionic/man8/mkudffs.8.html.
> Some Linux ISOs may have the MBR table for compatibility reasons
> for Windows. The MBR tale would contain the partition entry with
> start LBA0 and whole media size. There are two methods to check
> the filesystem in the CD-ROM:
> 1. MBR partition check (Windows)
> 2. Whole disk check (MAC OS)
> 
> UEFI doesn't have the MBR check for UDF and Eltorito. But it may
> pass the MBR check for such table and fail to detect the filesystem
> of UDF. Skip the MBR check if the MBR is added for Windows
> compatiblity so that the partition driver can continue UDF and
> ElTorito check.
> 
> Cc: Hao A Wu <hao.a.wu@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Signed-off-by: Zhichao Gao <zhichao.gao@intel.com>
> ---
>  .../Universal/Disk/PartitionDxe/Mbr.c         | 37 ++++++++++++++++---
>  1 file changed, 31 insertions(+), 6 deletions(-)
> 
> diff --git a/MdeModulePkg/Universal/Disk/PartitionDxe/Mbr.c
> b/MdeModulePkg/Universal/Disk/PartitionDxe/Mbr.c
> index f0c92aa09a..3830af1ea7 100644
> --- a/MdeModulePkg/Universal/Disk/PartitionDxe/Mbr.c
> +++ b/MdeModulePkg/Universal/Disk/PartitionDxe/Mbr.c
> @@ -39,6 +39,7 @@ PartitionValidMbr (
>    UINT32  StartingLBA;
>    UINT32  EndingLBA;
>    UINT32  NewEndingLBA;
> +  UINT32  SizeInLBA;
>    INTN    Index1;
>    INTN    Index2;
>    BOOLEAN MbrValid;
> @@ -51,13 +52,34 @@ PartitionValidMbr (
>    //
>    MbrValid = FALSE;
>    for (Index1 = 0; Index1 < MAX_MBR_PARTITIONS; Index1++) {
> -    if (Mbr->Partition[Index1].OSIndicator == 0x00 || UNPACK_UINT32 (Mbr-
> >Partition[Index1].SizeInLBA) == 0) {
> +    StartingLBA = UNPACK_UINT32 (Mbr->Partition[Index1].StartingLBA);
> +    SizeInLBA   = UNPACK_UINT32 (Mbr->Partition[Index1].SizeInLBA);
> +
> +    //
> +    // If the MBR with partition entry covering the ENTIRE disk, i.e. start at
> LBA0
> +    // with whole disk size, we treat it as an invalid MBR partition.
> +    //
> +    if ((StartingLBA == 0) &&
> +        (SizeInLBA == (LastLba + 1))) {
> +      //
> +      // Refer to the
> http://manpages.ubuntu.com/manpages/bionic/man8/mkudffs.8.html
> +      // "WHOLE DISK VS PARTITION"
> +      // Some linux ISOs may put the MBR table in the first 512 bytes for
> compatibility reasons with Windows.
> +      // Linux  kernel  ignores MBR table if contains partition which starts at
> sector 0.
> +      // Skip it because we don't have the partition check for UDF(El Torito
> compatible).
> +      // It would continue to do the whole disk check in the UDF routine.
> +      //
> +      DEBUG ((DEBUG_INFO, "PartitionValidMbr: MBR table has partition entry
> covering the ENTIRE disk. Don't treat it as a valid MBR.\n"));
> +
> +      return FALSE;
> +    }
> +
> +    if (Mbr->Partition[Index1].OSIndicator == 0x00 || SizeInLBA == 0) {
>        continue;
>      }
> 
>      MbrValid    = TRUE;
> -    StartingLBA = UNPACK_UINT32 (Mbr->Partition[Index1].StartingLBA);
> -    EndingLBA   = StartingLBA + UNPACK_UINT32 (Mbr-
> >Partition[Index1].SizeInLBA) - 1;
> +    EndingLBA   = StartingLBA + SizeInLBA - 1;
>      if (EndingLBA > LastLba) {
>        //
>        // Compatibility Errata:
> @@ -77,12 +99,15 @@ PartitionValidMbr (
>      }
> 
>      for (Index2 = Index1 + 1; Index2 < MAX_MBR_PARTITIONS; Index2++) {
> -      if (Mbr->Partition[Index2].OSIndicator == 0x00 || UNPACK_UINT32 (Mbr-
> >Partition[Index2].SizeInLBA) == 0) {
> +      StartingLBA = UNPACK_UINT32 (Mbr->Partition[Index2].StartingLBA);
> +      SizeInLBA   = UNPACK_UINT32 (Mbr->Partition[Index2].SizeInLBA);
> +
> +      if (Mbr->Partition[Index2].OSIndicator == 0x00 || SizeInLBA == 0) {
>          continue;
>        }
> 
> -      NewEndingLBA = UNPACK_UINT32 (Mbr->Partition[Index2].StartingLBA) +
> UNPACK_UINT32 (Mbr->Partition[Index2].SizeInLBA) - 1;
> -      if (NewEndingLBA >= StartingLBA && UNPACK_UINT32 (Mbr-
> >Partition[Index2].StartingLBA) <= EndingLBA) {
> +      NewEndingLBA = StartingLBA + SizeInLBA - 1;
> +      if (NewEndingLBA >= StartingLBA && StartingLBA <= EndingLBA) {
>          //
>          // This region overlaps with the Index1'th region
>          //
> --
> 2.21.0.windows.1