[PATCH] disk: gpt: verify alternate LBA points to last usable LBA

[Stefan Herbrechtsmeier]

Hi Heinrich,

Am 08.03.2021 um 18:38 schrieb Heinrich Schuchardt:
> On 08.03.21 17:07, Stefan Herbrechtsmeier wrote:
>> From: Stefan Herbrechtsmeier <stefan.herbrechtsmeier at weidmueller.com>
>>
>> The gpt command require the GPT backup header at the standard location
>> at the end of the device.Check the alternate LBA value before reading
>> the GPT backup header from the last usable LBA of the device.
> 
> If there is a bug in the gpt command, please, fix it instead of
> introducing constraints that don't exist in the UEFI specification.
> 
> The UEFI specification has:
> 
> "The backup GPT Partition Entry Array must be located after the Last
> Usable LBA and end before the backup GPT Header."

"If the primary GPT is invalid, the backup GPT is used instead and it is 
located on the last logical block on the disk." [UEFI specification 2.8, 
S. 120]

"Note that UEFI standard requires the backup header at the end of the 
device and partitioning tools can automatically relocate the header to 
follow the standard." [sfdisk man page, --relocate, gpt-bak-mini]

What should U-Boot do? I have a patch to use the backup GPT header if 
only the header itself is valid but I don't know if this behavior is 
correct.

Regards,
   Stefan