From f88814cc2578c121e6edef686365036db72af0ed Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Wed, 8 Jul 2020 13:01:57 +0300 Subject: efi/efivars: Expose RT service availability via efivars abstraction 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 --- include/linux/efi.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux') diff --git a/include/linux/efi.h b/include/linux/efi.h index bb35f3305e55..05c47f857383 100644 --- a/include/linux/efi.h +++ b/include/linux/efi.h @@ -994,6 +994,7 @@ int efivars_register(struct efivars *efivars, int efivars_unregister(struct efivars *efivars); struct kobject *efivars_kobject(void); +int efivar_supports_writes(void); int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *), void *data, bool duplicates, struct list_head *head); -- cgit v1.2.3