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

[Alper Nebi Yasak]

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
 	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"
-- 
2.40.1