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If a machine is reset while secrets are present in RAM, it may be possible for code executed after the reboot to extract those secrets from untouched memory. The Trusted Computing Group specified a mechanism for requesting that the firmware clear all RAM on reset before booting another OS. This is done by setting the MemoryOverwriteRequestControl variable at startup. If userspace can ensure that all secrets are removed as part of a controlled shutdown, it can reset this variable to 0 before triggering a hardware reboot. Signed-off-by: Matthew Garrett <mjg59@google.com> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Matt Fleming <matt@codeblueprint.co.uk> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-efi@vger.kernel.org Link: http://lkml.kernel.org/r/20170825155019.6740-2-ard.biesheuvel@linaro.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
173 lines
5.5 KiB
Plaintext
173 lines
5.5 KiB
Plaintext
menu "EFI (Extensible Firmware Interface) Support"
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depends on EFI
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config EFI_VARS
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tristate "EFI Variable Support via sysfs"
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depends on EFI
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default n
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help
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If you say Y here, you are able to get EFI (Extensible Firmware
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Interface) variable information via sysfs. You may read,
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write, create, and destroy EFI variables through this interface.
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Note that using this driver in concert with efibootmgr requires
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at least test release version 0.5.0-test3 or later, which is
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available from:
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<http://linux.dell.com/efibootmgr/testing/efibootmgr-0.5.0-test3.tar.gz>
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Subsequent efibootmgr releases may be found at:
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<http://github.com/vathpela/efibootmgr>
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config EFI_ESRT
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bool
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depends on EFI && !IA64
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default y
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config EFI_VARS_PSTORE
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tristate "Register efivars backend for pstore"
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depends on EFI_VARS && PSTORE
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default y
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help
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Say Y here to enable use efivars as a backend to pstore. This
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will allow writing console messages, crash dumps, or anything
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else supported by pstore to EFI variables.
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config EFI_VARS_PSTORE_DEFAULT_DISABLE
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bool "Disable using efivars as a pstore backend by default"
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depends on EFI_VARS_PSTORE
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default n
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help
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Saying Y here will disable the use of efivars as a storage
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backend for pstore by default. This setting can be overridden
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using the efivars module's pstore_disable parameter.
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config EFI_RUNTIME_MAP
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bool "Export efi runtime maps to sysfs"
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depends on X86 && EFI && KEXEC_CORE
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default y
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help
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Export efi runtime memory maps to /sys/firmware/efi/runtime-map.
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That memory map is used for example by kexec to set up efi virtual
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mapping the 2nd kernel, but can also be used for debugging purposes.
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See also Documentation/ABI/testing/sysfs-firmware-efi-runtime-map.
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config EFI_FAKE_MEMMAP
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bool "Enable EFI fake memory map"
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depends on EFI && X86
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default n
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help
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Saying Y here will enable "efi_fake_mem" boot option.
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By specifying this parameter, you can add arbitrary attribute
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to specific memory range by updating original (firmware provided)
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EFI memmap.
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This is useful for debugging of EFI memmap related feature.
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e.g. Address Range Mirroring feature.
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config EFI_MAX_FAKE_MEM
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int "maximum allowable number of ranges in efi_fake_mem boot option"
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depends on EFI_FAKE_MEMMAP
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range 1 128
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default 8
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help
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Maximum allowable number of ranges in efi_fake_mem boot option.
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Ranges can be set up to this value using comma-separated list.
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The default value is 8.
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config EFI_PARAMS_FROM_FDT
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bool
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help
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Select this config option from the architecture Kconfig if
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the EFI runtime support gets system table address, memory
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map address, and other parameters from the device tree.
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config EFI_RUNTIME_WRAPPERS
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bool
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config EFI_ARMSTUB
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bool
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config EFI_BOOTLOADER_CONTROL
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tristate "EFI Bootloader Control"
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depends on EFI_VARS
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default n
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---help---
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This module installs a reboot hook, such that if reboot() is
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invoked with a string argument NNN, "NNN" is copied to the
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"LoaderEntryOneShot" EFI variable, to be read by the
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bootloader. If the string matches one of the boot labels
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defined in its configuration, the bootloader will boot once
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to that label. The "LoaderEntryRebootReason" EFI variable is
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set with the reboot reason: "reboot" or "shutdown". The
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bootloader reads this reboot reason and takes particular
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action according to its policy.
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config EFI_CAPSULE_LOADER
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tristate "EFI capsule loader"
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depends on EFI
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help
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This option exposes a loader interface "/dev/efi_capsule_loader" for
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users to load EFI capsules. This driver requires working runtime
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capsule support in the firmware, which many OEMs do not provide.
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Most users should say N.
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config EFI_CAPSULE_QUIRK_QUARK_CSH
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boolean "Add support for Quark capsules with non-standard headers"
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depends on X86 && !64BIT
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select EFI_CAPSULE_LOADER
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default y
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help
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Add support for processing Quark X1000 EFI capsules, whose header
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layout deviates from the layout mandated by the UEFI specification.
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config EFI_TEST
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tristate "EFI Runtime Service Tests Support"
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depends on EFI
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default n
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help
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This driver uses the efi.<service> function pointers directly instead
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of going through the efivar API, because it is not trying to test the
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kernel subsystem, just for testing the UEFI runtime service
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interfaces which are provided by the firmware. This driver is used
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by the Firmware Test Suite (FWTS) for testing the UEFI runtime
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interfaces readiness of the firmware.
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Details for FWTS are available from:
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<https://wiki.ubuntu.com/FirmwareTestSuite>
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Say Y here to enable the runtime services support via /dev/efi_test.
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If unsure, say N.
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config APPLE_PROPERTIES
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bool "Apple Device Properties"
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depends on EFI_STUB && X86
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select EFI_DEV_PATH_PARSER
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select UCS2_STRING
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help
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Retrieve properties from EFI on Apple Macs and assign them to
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devices, allowing for improved support of Apple hardware.
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Properties that would otherwise be missing include the
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Thunderbolt Device ROM and GPU configuration data.
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If unsure, say Y if you have a Mac. Otherwise N.
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config RESET_ATTACK_MITIGATION
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bool "Reset memory attack mitigation"
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depends on EFI_STUB
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help
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Request that the firmware clear the contents of RAM after a reboot
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using the TCG Platform Reset Attack Mitigation specification. This
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protects against an attacker forcibly rebooting the system while it
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still contains secrets in RAM, booting another OS and extracting the
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secrets.
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endmenu
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config UEFI_CPER
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bool
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config EFI_DEV_PATH_PARSER
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bool
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depends on ACPI
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default n
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