linux-kernel - Re: [edk2] Corrupted EFI region

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Date:	Mon, 16 Sep 2013 18:25:22 +0200
From:	Laszlo Ersek <lersek@...hat.com>
To:	Josh Triplett <josh@...htriplett.org>
CC:	Matt Fleming <matt@...sole-pimps.org>, jerry.hoemann@...com,
	Andrew Fish <afish@...le.com>,
	edk2-devel@...ts.sourceforge.net, linux-efi@...r.kernel.org,
	Gleb Natapov <gleb@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Brian Richardson <brian.richardson@...el.com>,
	Colin Ian King <colin.king@...onical.com>,
	Randy Wright <rwright@...com>,
	Linn Crosetto <linn.crosetto@...com>, terry.lee@...com,
	samer.el-haj-mahmoud@...com, randy.pawell@...com, chrisp@...com,
	linda.knippers@...com, dong.wei@...com,
	"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
	Chao Zhang <chao.b.zhang@...el.com>,
	Yao Jiewen <jiewen.yao@...el.com>
Subject: Re: [edk2] Corrupted EFI region

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
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