kernel/git/stable/linux.git/drivers/firmware/efi/efivars.c, branch master

efi: vars: Remove deprecated 'efivars' sysfs interface

2022-06-24T18:40:19+00:00

Commit 5d9db883761a ("efi: Add support for a UEFI variable filesystem") dated Oct 5, 2012, introduced a new efivarfs pseudo-filesystem to replace the efivars sysfs interface that was used up to that point to expose EFI variables to user space. The main problem with the sysfs interface was that it only supported up to 1024 bytes of payload per file, whereas the underlying variables themselves are only bounded by a platform specific per-variable and global limit that is typically much higher than 1024 bytes. The deprecated sysfs interface is only enabled on x86 and Itanium, other EFI enabled architectures only support the efivarfs pseudo-filesystem. So let's finally rip off the band aid, and drop the old interface entirely. This will make it easier to refactor and clean up the underlying infrastructure that is shared between efivars, efivarfs and efi-pstore, and is long overdue for a makeover. Signed-off-by: Ard Biesheuvel

efi: vars: Use locking version to iterate over efivars linked lists

2022-06-24T18:40:19+00:00

Both efivars and efivarfs uses __efivar_entry_iter() to go over the linked list that shadows the list of EFI variables held by the firmware, but fail to call the begin/end helpers that are documented as a prerequisite. So switch to the proper version, which is efivar_entry_iter(). Given that in both cases, efivar_entry_remove() is invoked with the lock held already, don't take the lock there anymore. Signed-off-by: Ard Biesheuvel

efi: pstore: Omit efivars caching EFI varstore access layer

2022-06-24T18:40:19+00:00

Avoid the efivars layer and simply call the newly introduced EFI varstore helpers instead. This simplifies the code substantially, and also allows us to remove some hacks in the shared efivars layer that were added for efi-pstore specifically. In order to be able to delete the EFI variable associated with a record, store the UTF-16 name of the variable in the pstore record's priv field. That way, we don't have to make guesses regarding which variable the record may have been loaded from. Signed-off-by: Ard Biesheuvel

efi: vars: Don't drop lock in the middle of efivar_init()

2022-06-24T18:40:18+00:00

Even though the efivars_lock lock is documented as protecting the efivars->ops pointer (among other things), efivar_init() happily releases and reacquires the lock for every EFI variable that it enumerates. This used to be needed because the lock was originally a spinlock, which prevented the callback that is invoked for every variable from being able to sleep. However, releasing the lock could potentially invalidate the ops pointer, but more importantly, it might allow a SetVariable() runtime service call to take place concurrently, and the UEFI spec does not define how this affects an enumeration that is running in parallel using the GetNextVariable() runtime service, which is what efivar_init() uses. In the meantime, the lock has been converted into a semaphore, and the only reason we need to drop the lock is because the efivarfs pseudo filesystem driver will otherwise deadlock when it invokes the efivars API from the callback to create the efivar_entry items and insert them into the linked list. (EFI pstore is affected in a similar way) So let's switch to helpers that can be used while the lock is already taken. This way, we can hold on to the lock throughout the enumeration. Signed-off-by: Ard Biesheuvel

efi: use default_groups in kobj_type

2022-01-06T20:19:05+00:00

There are currently 2 ways to create a set of sysfs files for a kobj_type, through the default_attrs field, and the default_groups field. Move the firmware efi sysfs code to use default_groups field which has been the preferred way since aa30f47cf666 ("kobject: Add support for default attribute groups to kobj_type") so that we can soon get rid of the obsolete default_attrs field. Cc: Ard Biesheuvel Cc: linux-efi@vger.kernel.org Signed-off-by: Greg Kroah-Hartman Signed-off-by: Ard Biesheuvel

efi: efivars: limit availability to X86 builds

2020-09-29T17:40:57+00:00

CONFIG_EFI_VARS controls the code that exposes EFI variables via sysfs entries, which was deprecated before support for non-Intel architectures was added to EFI. So let's limit its availability to Intel architectures for the time being, and hopefully remove it entirely in the not too distant future. While at it, let's remove the module alias so that the module is no longer loaded automatically. Signed-off-by: Ard Biesheuvel

efi: efivars: un-export efivars_sysfs_init()

2020-09-29T17:40:57+00:00

efivars_sysfs_init() is only used locally in the source file that defines it, so make it static and unexport it. Signed-off-by: Ard Biesheuvel

efi: pstore: disentangle from deprecated efivars module

2020-09-29T17:40:57+00:00

The EFI pstore implementation relies on the 'efivars' abstraction, which encapsulates the EFI variable store in a way that can be overridden by other backing stores, like the Google SMI one. On top of that, the EFI pstore implementation also relies on the efivars.ko module, which is a separate layer built on top of the 'efivars' abstraction that exposes the [deprecated] sysfs entries for each variable that exists in the backing store. Since the efivars.ko module is deprecated, and all users appear to have moved to the efivarfs file system instead, let's prepare for its removal, by removing EFI pstore's dependency on it. Signed-off-by: Ard Biesheuvel

efi/efivars: Expose RT service availability via efivars abstraction

2020-07-09T07:14:29+00:00

Commit bf67fad19e493b ("efi: Use more granular check for availability for variable services") introduced a check into the efivarfs, efi-pstore and other drivers that aborts loading of the module if not all three variable runtime services (GetVariable, SetVariable and GetNextVariable) are supported. However, this results in efivarfs being unavailable entirely if only SetVariable support is missing, which is only needed if you want to make any modifications. Also, efi-pstore and the sysfs EFI variable interface could be backed by another implementation of the 'efivars' abstraction, in which case it is completely irrelevant which services are supported by the EFI firmware. So make the generic 'efivars' abstraction dependent on the availibility of the GetVariable and GetNextVariable EFI runtime services, and add a helper 'efivar_supports_writes()' to find out whether the currently active efivars abstraction supports writes (and wire it up to the availability of SetVariable for the generic one). Then, use the efivar_supports_writes() helper to decide whether to permit efivarfs to be mounted read-write, and whether to enable efi-pstore or the sysfs EFI variable interface altogether. Fixes: bf67fad19e493b ("efi: Use more granular check for availability for variable services") Reported-by: Heinrich Schuchardt Acked-by: Ilias Apalodimas Tested-by: Ilias Apalodimas Signed-off-by: Ard Biesheuvel

efi/efivars: Add missing kobject_put() in sysfs entry creation error path

2020-05-22T16:19:06+00:00

The documentation provided by kobject_init_and_add() clearly spells out the need to call kobject_put() on the kobject if an error is returned. Add this missing call to the error path. Cc: Reported-by: 亿一 Signed-off-by: Ard Biesheuvel