[PATCH] efi_loader: Increase default variable store size to 32K

[Heinrich Schuchardt]

On 7/8/23 17:21, Alper Nebi Yasak wrote:
> Debian's arm64 UEFI Secure Boot shim makes the EFI variable store run
> out of space while mirroring its MOK database to variables. This can be
> observed in QEMU like so:
>
>    $ tools/buildman/buildman -o build/qemu_arm64 --boards=qemu_arm64 -w
>    $ cd build/qemu_arm64
>    $ curl -L -o debian.iso \
>        https://cdimage.debian.org/debian-cd/current/arm64/iso-cd/debian-12.0.0-arm64-netinst.iso
>    $ qemu-system-aarch64 \
>        -nographic -bios u-boot.bin \
>        -machine virt -cpu cortex-a53 -m 1G -smp 2 \
>        -drive if=virtio,file=debian.iso,index=0,format=raw,readonly=on,media=cdrom
>    [...]
>    => # interrupt autoboot
>    => env set -e -bs -nv -rt -guid 605dab50-e046-4300-abb6-3dd810dd8b23 SHIM_VERBOSE 1
>    => boot
>    [...]
>    mok.c:296:mirror_one_esl() SetVariable("MokListXRT43", ... varsz=0x4C) = Out of Resources
>    mok.c:452:mirror_mok_db() esd:0x7DB92D20 adj:0x30
>    Failed to set MokListXRT: Out of Resources
>    mok.c:767:mirror_one_mok_variable() mirror_mok_db("MokListXRT",  datasz=17328) returned Out of Resources
>    mok.c:812:mirror_one_mok_variable() returning Out of Resources
>    Could not create MokListXRT: Out of Resources
>    [...]
>    Welcome to GRUB!
>
> This would normally be fine as shim would continue to run grubaa64.efi,
> but shim's error handling code for this case has a bug [1] that causes a
> synchronous abort on at least chromebook_kevin (but apparently not on
> QEMU arm64).
>
> Double the default variable store size so the variables fit. There is a
> note about this value matching PcdFlashNvStorageVariableSize when
> EFI_MM_COMM_TEE is enabled, so keep the old default in that case.
>
> [1] https://github.com/rhboot/shim/pull/577
>
> Signed-off-by: Alper Nebi Yasak <alpernebiyasak at gmail.com>
> ---
> I'm not very familiar with EFI things, apologies if this default
> should not be changed (consider this a bug report in that case).
>
>   lib/efi_loader/Kconfig | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
> index c5835e6ef61a..0660d1174902 100644
> --- a/lib/efi_loader/Kconfig
> +++ b/lib/efi_loader/Kconfig
> @@ -96,7 +96,8 @@ endif
>
>   config EFI_VAR_BUF_SIZE
>   	int "Memory size of the UEFI variable store"
> -	default 16384
> +	default 16384 if EFI_MM_COMM_TEE
> +	default 32768

https://learn.microsoft.com/en-us/previous-versions/windows/hardware/cert-program/windows-hardware-certification-requirements-for-client-and-server-systems

requires 64 KiB.

Best regards

Heinrich

>   	range 4096 2147483647
>   	help
>   	  This defines the size in bytes of the memory area reserved for keeping
> @@ -106,7 +107,7 @@ config EFI_VAR_BUF_SIZE
>   	  match the value of PcdFlashNvStorageVariableSize used to compile the
>   	  StandAloneMM module.
>
> -	  Minimum 4096, default 16384.
> +	  Minimum 4096, default 32768, or 16384 when using StandAloneMM.
>
>   config EFI_GET_TIME
>   	bool "GetTime() runtime service"