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Apple's EFI drivers supply device properties which are needed to support
Macs optimally. They contain vital information which cannot be obtained
any other way (e.g. Thunderbolt Device ROM). They're also used to convey
the current device state so that OS drivers can pick up where EFI
drivers left (e.g. GPU mode setting).
There's an EFI driver dubbed "AAPL,PathProperties" which implements a
per-device key/value store. Other EFI drivers populate it using a custom
protocol. The macOS bootloader /System/Library/CoreServices/boot.efi
retrieves the properties with the same protocol. The kernel extension
AppleACPIPlatform.kext subsequently merges them into the I/O Kit
registry (see ioreg(8)) where they can be queried by other kernel
extensions and user space.
This commit extends the efistub to retrieve the device properties before
ExitBootServices is called. It assigns them to devices in an fs_initcall
so that they can be queried with the API in <linux/property.h>.
Note that the device properties will only be available if the kernel is
booted with the efistub. Distros should adjust their installers to
always use the efistub on Macs. grub with the "linux" directive will not
work unless the functionality of this commit is duplicated in grub.
(The "linuxefi" directive should work but is not included upstream as of
this writing.)
The custom protocol has GUID 91BD12FE-F6C3-44FB-A5B7-5122AB303AE0 and
looks like this:
typedef struct {
unsigned long version; /* 0x10000 */
efi_status_t (*get) (
IN struct apple_properties_protocol *this,
IN struct efi_dev_path *device,
IN efi_char16_t *property_name,
OUT void *buffer,
IN OUT u32 *buffer_len);
/* EFI_SUCCESS, EFI_NOT_FOUND, EFI_BUFFER_TOO_SMALL */
efi_status_t (*set) (
IN struct apple_properties_protocol *this,
IN struct efi_dev_path *device,
IN efi_char16_t *property_name,
IN void *property_value,
IN u32 property_value_len);
/* allocates copies of property name and value */
/* EFI_SUCCESS, EFI_OUT_OF_RESOURCES */
efi_status_t (*del) (
IN struct apple_properties_protocol *this,
IN struct efi_dev_path *device,
IN efi_char16_t *property_name);
/* EFI_SUCCESS, EFI_NOT_FOUND */
efi_status_t (*get_all) (
IN struct apple_properties_protocol *this,
OUT void *buffer,
IN OUT u32 *buffer_len);
/* EFI_SUCCESS, EFI_BUFFER_TOO_SMALL */
} apple_properties_protocol;
Thanks to Pedro Vilaça for this blog post which was helpful in reverse
engineering Apple's EFI drivers and bootloader:
https://reverse.put.as/2016/06/25/apple-efi-firmware-passwords-and-the-scbo-myth/
If someone at Apple is reading this, please note there's a memory leak
in your implementation of the del() function as the property struct is
freed but the name and value allocations are not.
Neither the macOS bootloader nor Apple's EFI drivers check the protocol
version, but we do to avoid breakage if it's ever changed. It's been the
same since at least OS X 10.6 (2009).
The get_all() function conveniently fills a buffer with all properties
in marshalled form which can be passed to the kernel as a setup_data
payload. The number of device properties is dynamic and can change
between a first invocation of get_all() (to determine the buffer size)
and a second invocation (to retrieve the actual buffer), hence the
peculiar loop which does not finish until the buffer size settles.
The macOS bootloader does the same.
The setup_data payload is later on unmarshalled in an fs_initcall. The
idea is that most buses instantiate devices in "subsys" initcall level
and drivers are usually bound to these devices in "device" initcall
level, so we assign the properties in-between, i.e. in "fs" initcall
level.
This assumes that devices to which properties pertain are instantiated
from a "subsys" initcall or earlier. That should always be the case
since on macOS, AppleACPIPlatformExpert::matchEFIDevicePath() only
supports ACPI and PCI nodes and we've fully scanned those buses during
"subsys" initcall level.
The second assumption is that properties are only needed from a "device"
initcall or later. Seems reasonable to me, but should this ever not work
out, an alternative approach would be to store the property sets e.g. in
a btree early during boot. Then whenever device_add() is called, an EFI
Device Path would have to be constructed for the newly added device,
and looked up in the btree. That way, the property set could be assigned
to the device immediately on instantiation. And this would also work for
devices instantiated in a deferred fashion. It seems like this approach
would be more complicated and require more code. That doesn't seem
justified without a specific use case.
For comparison, the strategy on macOS is to assign properties to objects
in the ACPI namespace (AppleACPIPlatformExpert::mergeEFIProperties()).
That approach is definitely wrong as it fails for devices not present in
the namespace: The NHI EFI driver supplies properties for attached
Thunderbolt devices, yet on Macs with Thunderbolt 1 only one device
level behind the host controller is described in the namespace.
Consequently macOS cannot assign properties for chained devices. With
Thunderbolt 2 they started to describe three device levels behind host
controllers in the namespace but this grossly inflates the SSDT and
still fails if the user daisy-chained more than three devices.
We copy the property names and values from the setup_data payload to
swappable virtual memory and afterwards make the payload available to
the page allocator. This is just for the sake of good housekeeping, it
wouldn't occupy a meaningful amount of physical memory (4444 bytes on my
machine). Only the payload is freed, not the setup_data header since
otherwise we'd break the list linkage and we cannot safely update the
predecessor's ->next link because there's no locking for the list.
The payload is currently not passed on to kexec'ed kernels, same for PCI
ROMs retrieved by setup_efi_pci(). This can be added later if there is
demand by amending setup_efi_state(). The payload can then no longer be
made available to the page allocator of course.
Tested-by: Lukas Wunner <lukas@wunner.de> [MacBookPro9,1]
Tested-by: Pierre Moreau <pierre.morrow@free.fr> [MacBookPro11,3]
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Andreas Noever <andreas.noever@gmail.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pedro Vilaça <reverser@put.as>
Cc: Peter Jones <pjones@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: grub-devel@gnu.org
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/20161112213237.8804-9-matt@codeblueprint.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>
154 lines
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154 lines
4.8 KiB
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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_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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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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