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authorLukas Wunner <lukas@wunner.de>2016-11-12 22:32:36 +0100
committerIngo Molnar <mingo@kernel.org>2016-11-13 08:23:16 +0100
commit58c5475aba67706b31d9237808d5d3d54074e5ea (patch)
tree812358c3b6af51c93ef855450aded9d65501ce89 /drivers/firmware/efi/Kconfig
parentefi: Allow bitness-agnostic protocol calls (diff)
downloadlinux-58c5475aba67706b31d9237808d5d3d54074e5ea.tar.xz
linux-58c5475aba67706b31d9237808d5d3d54074e5ea.zip
x86/efi: Retrieve and assign Apple device properties
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>
Diffstat (limited to 'drivers/firmware/efi/Kconfig')
-rw-r--r--drivers/firmware/efi/Kconfig13
1 files changed, 13 insertions, 0 deletions
diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
index 893fda48fcdd..2e78b0b96d74 100644
--- a/drivers/firmware/efi/Kconfig
+++ b/drivers/firmware/efi/Kconfig
@@ -129,6 +129,19 @@ config EFI_TEST
Say Y here to enable the runtime services support via /dev/efi_test.
If unsure, say N.
+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.
+
endmenu
config UEFI_CPER