On Mon, Jun 25, 2018 at 08:34:05AM +0200, Ard Biesheuvel wrote:
> 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,
Just for comment - this too is considered an anomaly and will
eventually be phased out. (Some part of the functionality may be
retained in the form of overlay management.)
> - 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@xxxxxxxxxx>
Acked-by: Leif Lindholm <leif.lindholm@xxxxxxxxxx>
> ---
> drivers/firmware/efi/Kconfig | 12 ++++++++++++
> drivers/firmware/efi/libstub/arm-stub.c | 7 ++++---
> 2 files changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
> index 781a4a337557..fc1cb2961d5b 100644
> --- a/drivers/firmware/efi/Kconfig
> +++ b/drivers/firmware/efi/Kconfig
> @@ -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, and so this option is mostly for development
> + purposes only.
> +
> config EFI_BOOTLOADER_CONTROL
> tristate "EFI Bootloader Control"
> depends on EFI_VARS
> diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c
> index 01a9d78ee415..c98b1856fc3d 100644
> --- a/drivers/firmware/efi/libstub/arm-stub.c
> +++ b/drivers/firmware/efi/libstub/arm-stub.c
> @@ -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=",
> --
> 2.11.0
>
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