Re: [edk2-devel] [PATCH] MdeModulePkg/PartitionDxe: Ignore PMBR BootIndicator per UEFI spec

["Laszlo Ersek" <lersek@redhat.com>]

On 07/05/21 11:36, Neal Gompa wrote:
> Per UEFI Spec 2.8 (UEFI_Spec_2_8_final.pdf, page 114)
> 5.2.3 Protective MBR
> Table 20. Protective MBR Partition Record protecting the entire disk
> 
> The description for BootIndicator states the following:
> 
>> Set to 0x00 to indicate a non-bootable partition. If set to any
>> value other than 0x00 the behavior of this flag on non-UEFI
>> systems is undefined. Must be ignored by UEFI implementations.
> 
> Unfortunately, we have been incorrectly assuming that the
> BootIndicator value must be 0x00, which leads to problems
> when the 'pmbr_boot' flag is set on a disk containing a GPT
> (such as with GNU parted). When the flag is set, the value
> changes to 0x01, causing this check to fail and the system
> is rendered unbootable despite it being valid from the
> perspective of the UEFI spec.
> 
> To resolve this, we drop the check for the BootIndicator
> so that we stop caring about the value set there, which
> restores the capability to boot such disks.
> 
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3474
> 
> Cc: Chris Murphy <chrismurphy@fedoraproject.org>
> Cc: David Duncan <davdunc@amazon.com>
> Cc: Lazlo Ersek <lersek@redhat.com>
> Cc: Hao A Wu <hao.a.wu@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Zhichao Gao <zhichao.gao@intel.com>
> 
> Signed-off-by: Neal Gompa <ngompa@fedoraproject.org>
> ---
>  MdeModulePkg/Universal/Disk/PartitionDxe/Gpt.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/MdeModulePkg/Universal/Disk/PartitionDxe/Gpt.c b/MdeModulePkg/Universal/Disk/PartitionDxe/Gpt.c
> index aefb2d6ecb3f..efaff5e0808f 100644
> --- a/MdeModulePkg/Universal/Disk/PartitionDxe/Gpt.c
> +++ b/MdeModulePkg/Universal/Disk/PartitionDxe/Gpt.c
> @@ -264,8 +264,7 @@ PartitionInstallGptChildHandles (
>    // Verify that the Protective MBR is valid
>    //
>    for (Index = 0; Index < MAX_MBR_PARTITIONS; Index++) {
> -    if (ProtectiveMbr->Partition[Index].BootIndicator == 0x00 &&
> -        ProtectiveMbr->Partition[Index].OSIndicator == PMBR_GPT_PARTITION &&
> +    if (ProtectiveMbr->Partition[Index].OSIndicator == PMBR_GPT_PARTITION &&
>          UNPACK_UINT32 (ProtectiveMbr->Partition[Index].StartingLBA) == 1
>          ) {
>        break;
> 

Reviewed-by: Laszlo Ersek <lersek@redhat.com>

Thanks
Laszlo