# SPDX-License-Identifier: GPL-2.0-only
menu "EFI (Extensible Firmware Interface) Support"
depends on EFI
config EFI_ESRT
bool
depends on EFI && !IA64
default y
config EFI_VARS_PSTORE
tristate "Register efivars backend for pstore"
depends on PSTORE
select UCS2_STRING
default y
help
Say Y here to enable use efivars as a backend to pstore. This
will allow writing console messages, crash dumps, or anything
else supported by pstore to EFI variables.
config EFI_VARS_PSTORE_DEFAULT_DISABLE
bool "Disable using efivars as a pstore backend by default"
depends on EFI_VARS_PSTORE
default n
help
Saying Y here will disable the use of efivars as a storage
backend for pstore by default. This setting can be overridden
using the efivars module's pstore_disable parameter.
config EFI_SOFT_RESERVE
bool "Reserve EFI Specific Purpose Memory"
depends on EFI && EFI_STUB && ACPI_HMAT
default ACPI_HMAT
help
On systems that have mixed performance classes of memory EFI
may indicate specific purpose memory with an attribute (See
EFI_MEMORY_SP in UEFI 2.8). A memory range tagged with this
attribute may have unique performance characteristics compared
to the system's general purpose "System RAM" pool. On the
expectation that such memory has application specific usage,
and its base EFI memory type is "conventional" answer Y to
arrange for the kernel to reserve it as a "Soft Reserved"
resource, and set aside for direct-access (device-dax) by
default. The memory range can later be optionally assigned to
the page allocator by system administrator policy via the
device-dax kmem facility. Say N to have the kernel treat this
memory as "System RAM" by default.
If unsure, say Y.
config EFI_DXE_MEM_ATTRIBUTES
bool "Adjust memory attributes in EFISTUB"
depends on EFI && EFI_STUB && X86
default y
help
UEFI specification does not guarantee all memory to be
accessible for both write and execute as the kernel expects
it to be.
Use DXE services to check and alter memory protection
attributes during boot via EFISTUB to ensure that memory
ranges used by the kernel are writable and executable.
config EFI_PARAMS_FROM_FDT
bool
help
Select this config option from the architecture Kconfig if
the EFI runtime support gets system table address, memory
map address, and other parameters from the device tree.
config EFI_RUNTIME_WRAPPERS
bool
config EFI_GENERIC_STUB
bool
config EFI_ZBOOT
bool "Enable the generic EFI decompressor"
depends on EFI_GENERIC_STUB && !ARM
select HAVE_KERNEL_GZIP
select HAVE_KERNEL_LZ4
select HAVE_KERNEL_LZMA
select HAVE_KERNEL_LZO
select HAVE_KERNEL_XZ
select HAVE_KERNEL_ZSTD
help
Create the bootable image as an EFI application that carries the
actual kernel image in compressed form, and decompresses it into
memory before executing it via LoadImage/StartImage EFI boot service
calls. For compatibility with non-EFI loaders, the payload can be
decompressed and executed by the loader as well, provided that the
loader implements the decompression algorithm and that non-EFI boot
is supported by the encapsulated image. (The compression algorithm
used is described in the zboot image header)
config EFI_ARMSTUB_DTB_LOADER
bool "Enable the DTB loader"
depends on EFI_GENERIC_STUB && !RISCV && !LOONGARCH
default y
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.
If the device tree is provided by the platform or by
the bootloader this option may not be needed.
But, for various development reasons and to maintain existing
functionality for bootloaders that do not have such support
this option is necessary.
config EFI_BOOTLOADER_CONTROL
tristate "EFI Bootloader Control"
select UCS2_STRING
default n
help
This module installs a reboot hook, such that if reboot() is
invoked with a string argument NNN, "NNN" is copied to the
"LoaderEntryOneShot" EFI variable, to be read by the
bootloader. If the string matches one of the boot labels
defined in its configuration, the bootloader will boot once
to that label. The "LoaderEntryRebootReason" EFI variable is
set with the reboot reason: "reboot" or "shutdown". The
bootloader reads this reboot reason and takes particular
action according to its policy.
config EFI_CAPSULE_LOADER
tristate "EFI capsule loader"
depends on EFI && !IA64
help
This option exposes a loader interface "/dev/efi_capsule_loader" for
users to load EFI capsules. This driver requires working runtime
capsule support in the firmware, which many OEMs do not provide.
Most users should say N.
config EFI_CAPSULE_QUIRK_QUARK_CSH
bool "Add support for Quark capsules with non-standard headers"
depends on X86 && !64BIT
select EFI_CAPSULE_LOADER
default y
help
Add support for processing Quark X1000 EFI capsules, whose header
layout deviates from the layout mandated by the UEFI specification.
config EFI_TEST
tristate "EFI Runtime Service Tests Support"
depends on EFI
default n
help
This driver uses the efi.<service> function pointers directly instead
of going through the efivar API, because it is not trying to test the
kernel subsystem, just for testing the UEFI runtime service
interfaces which are provided by the firmware. This driver is used
by the Firmware Test Suite (FWTS) for testing the UEFI runtime
interfaces readiness of the firmware.
Details for FWTS are available from:
<https://wiki.ubuntu.com/FirmwareTestSuite>
Say Y here to enable the runtime services support via /dev/efi_test.
If unsure, say N.
config EFI_DEV_PATH_PARSER
bool
config APPLE_PROPERTIES
bool "Apple Device Properties"
depends on EFI_STUB && X86
select EFI_DEV_PATH_PARSER
select UCS2_STRING
help
Retrieve properties from EFI on Apple Macs and assign them to
devices, allowing for improved support of Apple hardware.
Properties that would otherwise be missing include the
Thunderbolt Device ROM and GPU configuration data.
If unsure, say Y if you have a Mac. Otherwise N.
config RESET_ATTACK_MITIGATION
bool "Reset memory attack mitigation"
depends on EFI_STUB
help
Request that the firmware clear the contents of RAM after a reboot
using the TCG Platform Reset Attack Mitigation specification. This
protects against an attacker forcibly rebooting the system while it
still contains secrets in RAM, booting another OS and extracting the
secrets. This should only be enabled when userland is configured to
clear the MemoryOverwriteRequest flag on clean shutdown after secrets
have been evicted, since otherwise it will trigger even on clean
reboots.
config EFI_RCI2_TABLE
bool "EFI Runtime Configuration Interface Table Version 2 Support"
depends on X86 || COMPILE_TEST
help
Displays the content of the Runtime Configuration Interface
Table version 2 on Dell EMC PowerEdge systems as a binary
attribute 'rci2' under /sys/firmware/efi/tables directory.
RCI2 table contains BIOS HII in XML format and is used to populate
BIOS setup page in Dell EMC OpenManage Server Administrator tool.
The BIOS setup page contains BIOS tokens which can be configured.
Say Y here for Dell EMC PowerEdge systems.
config EFI_DISABLE_PCI_DMA
bool "Clear Busmaster bit on PCI bridges during ExitBootServices()"
help
Disable the busmaster bit in the control register on all PCI bridges
while calling ExitBootServices() and passing control to the runtime
kernel. System firmware may configure the IOMMU to prevent malicious
PCI devices from being able to attack the OS via DMA. However, since
firmware can't guarantee that the OS is IOMMU-aware, it will tear
down IOMMU configuration when ExitBootServices() is called. This
leaves a window between where a hostile device could still cause
damage before Linux configures the IOMMU again.
If you say Y here, the EFI stub will clear the busmaster bit on all
PCI bridges before ExitBootServices() is called. This will prevent
any malicious PCI devices from being able to perform DMA until the
kernel reenables busmastering after configuring the IOMMU.
This option will cause failures with some poorly behaved hardware
and should not be enabled without testing. The kernel commandline
options "efi=disable_early_pci_dma" or "efi=no_disable_early_pci_dma"
may be used to override this option.
config EFI_EARLYCON
def_bool y
depends on SERIAL_EARLYCON && !ARM && !IA64
select FONT_SUPPORT
select ARCH_USE_MEMREMAP_PROT
config EFI_CUSTOM_SSDT_OVERLAYS
bool "Load custom ACPI SSDT overlay from an EFI variable"
depends on ACPI
default ACPI_TABLE_UPGRADE
help
Allow loading of an ACPI SSDT overlay from an EFI variable specified
by a kernel command line option.
See Documentation/admin-guide/acpi/ssdt-overlays.rst for more
information.
config EFI_DISABLE_RUNTIME
bool "Disable EFI runtime services support by default"
default y if PREEMPT_RT
help
Allow to disable the EFI runtime services support by default. This can
already be achieved by using the efi=noruntime option, but it could be
useful to have this default without any kernel command line parameter.
The EFI runtime services are disabled by default when PREEMPT_RT is
enabled, because measurements have shown that some EFI functions calls
might take too much time to complete, causing large latencies which is
an issue for Real-Time kernels.
This default can be overridden by using the efi=runtime option.
config EFI_COCO_SECRET
bool "EFI Confidential Computing Secret Area Support"
help
Confidential Computing platforms (such as AMD SEV) allow the
Guest Owner to securely inject secrets during guest VM launch.
The secrets are placed in a designated EFI reserved memory area.
In order to use the secrets in the kernel, the location of the secret
area (as published in the EFI config table) must be kept.
If you say Y here, the address of the EFI secret area will be kept
for usage inside the kernel. This will allow the
virt/coco/efi_secret module to access the secrets, which in turn
allows userspace programs to access the injected secrets.
config UNACCEPTED_MEMORY
bool
depends on EFI_STUB
help
Some Virtual Machine platforms, such as Intel TDX, require
some memory to be "accepted" by the guest before it can be used.
This mechanism helps prevent malicious hosts from making changes
to guest memory.
UEFI specification v2.9 introduced EFI_UNACCEPTED_MEMORY memory type.
This option adds support for unaccepted memory and makes such memory
usable by the kernel.
config EFI_EMBEDDED_FIRMWARE
bool
select CRYPTO_LIB_SHA256
endmenu
config UEFI_CPER
bool
config UEFI_CPER_ARM
bool
depends on UEFI_CPER && ( ARM || ARM64 )
default y
config UEFI_CPER_X86
bool
depends on UEFI_CPER && X86
default y