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efi/libstub/arm: Add opt-in Kconfig option for the DTB loader 

There are various ways a platform can provide a device tree binary
to the kernel, with different levels of sophistication:

- ideally, the UEFI firmware, which is tightly coupled with the
  platform, provides a device tree image directly as a UEFI
  configuration table, and typically permits the contents to be
  manipulated either via menu options or via UEFI environment
  variables that specify a replacement image,

- GRUB for ARM has a 'devicetree' directive which allows a device
  tree image to be loaded from any location accessible to GRUB, and
  supersede the one provided by the firmware,

- the EFI stub implements a dtb= command line option that allows a
  device tree image to be loaded from a file residing in the same
  file system as the one the kernel image was loaded from.

The dtb= command line option was never intended to be more than a
development feature, to allow the other options to be implemented
in parallel. So let's make it an opt-in feature that is disabled
by default, but can be re-enabled at will.

Note that we already disable the dtb= command line option when we
detect that we are running with UEFI Secure Boot enabled.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Alexander Graf <agraf@suse.de>
Acked-by: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20180711094040.12506-7-ard.biesheuvel@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Ard Biesheuvel 2018-07-11 11:40:38 +02:00 committed by Ingo Molnar
parent f5dcc214aa
commit 3d7ee348aa
2 changed files with 16 additions and 3 deletions
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12
drivers/firmware/efi/Kconfig
View File

@ -87,6 +87,18 @@ config EFI_RUNTIME_WRAPPERS
config EFI_ARMSTUB
bool
config EFI_ARMSTUB_DTB_LOADER
bool "Enable the DTB loader"
depends on EFI_ARMSTUB
help
Select this config option to add support for the dtb= command
line parameter, allowing a device tree blob to be loaded into
memory from the EFI System Partition by the stub.
The device tree is typically provided by the platform or by
the bootloader, so this option is mostly for development
purposes only.
config EFI_BOOTLOADER_CONTROL
tristate "EFI Bootloader Control"
depends on EFI_VARS

7
drivers/firmware/efi/libstub/arm-stub.c
View File

@ -202,9 +202,10 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table,
* 'dtb=' unless UEFI Secure Boot is disabled. We assume that secure
* boot is enabled if we can't determine its state.
*/
if (secure_boot != efi_secureboot_mode_disabled &&
strstr(cmdline_ptr, "dtb=")) {
pr_efi(sys_table, "Ignoring DTB from command line.\n");
if (!IS_ENABLED(CONFIG_EFI_ARMSTUB_DTB_LOADER) ||
secure_boot != efi_secureboot_mode_disabled) {
if (strstr(cmdline_ptr, "dtb="))
pr_efi(sys_table, "Ignoring DTB from command line.\n");
} else {
status = handle_cmdline_files(sys_table, image, cmdline_ptr,
"dtb=",