Re: [edk2] Corrupted EFI region

Laszlo Ersek
2013-09-16T16:25:22Z

On 09/16/13 17:57, Josh Triplett wrote:

>> The edk2 commit that flipped the memory type underneath the image data
>> from EfiReservedMemoryType to EfiBootServicesData is:
>>
>> https://github.com/tianocore/edk2/commit/4c58575e
>>
>> I think this commit is wrong. It's fine for OSPM to release the image
>> data at some point, but not right after ExitBootServices(), because
>> referencing pointers in ACPI tables survive strictly longer.
>>
>> ... Actually, the commit does follow the ACPI spec 5.0:
>>
>> 5.2.22.4 Image Address
>>
>> The Image Address contains the location in memory where an
>> in-memory copy of the boot image can be found. The image should be
>> stored in EfiBootServicesData, allowing the system to reclaim
>> the memory when the image is no longer needed.
>>
>> The ACPI spec 5.0 should recommend EfiACPIReclaimMemory here IMO. (I
>> take the current wording ("should be stored") as a recommendation only.)
>
> I agree that UEFI *should* store the BGRT in EfiACPIReclaimMemory, but
> in practice the UEFI firmware I've seen with a BGRT does follow that
> recommendation and store it in EfiBootServicesData. So, even if the
> recommendation in the spec changed, the kernel would still have to
> accomodate both possibilities.

Just for the theoretical debate:

The edk2 commit linked above is 5 days old. All UEFI firmware in the
wild (on released hardware) should be using EfiReservedMemoryType (the
pre-patch memory type), which is even stricter.

EfiReservedMemoryType can never be released & repurposed, so it should
make no difference for crash kernel allocation, shouldn't it?

- call efi_free_boot_services() -- doesn't touch the image data (which
is in RAM of EfiReservedMemoryType),
- reserve crash kernel,
- access BGRT via ACPI.

BGRT had appeared in edk2 with

https://github.com/tianocore/edk2/commit/0284e90c

and EfiReservedMemoryType used to be the allocation type until commit
4c58575e.

Or are you alluding to UEFI firmware that's not based on TianoCore?

Laszlo