[PATCH v1 0/4] Enable SetvariableRT

[Mark Kettenis]

> From: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> 
> Hi all,
> 
> This is an updated version of [0].
> 
> When EFI variables are stored on file we don't allow SetVariableRT,
> since the OS doesn't know how to access or write that file.  At the same
> time keeping the U-Boot drivers alive in runtime sections and performing
> writes from the firmware is dangerous -- if at all possible.
> 
> For GetVariableRT  we copy runtime variables in RAM and expose them to
> the OS. Add a Kconfig option and provide SetVariableRT using the same
> memory back end. The OS will be responsible for syncing the RAM contents
> to the file, otherwise any changes made during runtime won't persist
> reboots.
> 
> It's worth noting that the variable store format is defined in EBBR [1]
> and authenticated variables are explicitly prohibited, since they have
> to be stored on a medium that's tamper and rollback protected.
> 
> The original RFC was just enabling the memory back end. This is a more
> complete version and we should be able, with small adjustments of
> userspace tools, fix SetVariableRT. If enabled the firmware will add two
> new RO EFI variables after ExitBootServices.
> 
> RTStorageVolatile -- contains the filename, relative to the ESP
> VarToFile -- an EFI variable that holds all the BS,RT, NV variables and can
> be copied to the file defined by RTStorageVolatile.
> 
> If any errors occur during the variable init, the firmware will delete them
> and adjust the RT_PROP table accordingly, disabling SetvarRT.
> 
> - pre-patch
> $~ mount | grep efiva
> efivarfs on /sys/firmware/efi/efivars type efivarfs (ro,nosuid,nodev,noexec,relatime)
> 
> $~ efibootmgr -n 0001
> Could not set BootNext: Read-only file system
> 
> - post-patch
> $~ mount | grep efiva
> efivarfs on /sys/firmware/efi/efivars type efivarfs (rw,nosuid,nodev,noexec,relatime)
> , disabling SetvarRT.
> $~ efibootmgr -n 0001
> BootNext: 0001
> BootCurrent: 0000
> BootOrder: 0000,0001
> Boot0000* debian        HD(1,GPT,bdae5610-3331-4e4d-9466-acb5caf0b4a6,0x800,0x100000)/File(EFI\debian\grubaa64.efi)
> Boot0001* virtio 0      VenHw(e61d73b9-a384-4acc-aeab-82e828f3628b,0000000000000000)/VenHw(e61d73b9-a384-4acc-aeab-82e828f3628b,850000001f000000)/VenHw(e61d73b9-a384-4acc-aeab-82e828f3628b,1600850000000000){auto_created_boot_option}
> 
> $~ efivar -p -n 8be4df61-93ca-11d2-aa0d-00e098032b8c-BootNext
> GUID: 8be4df61-93ca-11d2-aa0d-00e098032b8c
> Name: "BootNext"
> Attributes:
>         Non-Volatile
>         Boot Service Access
>         Runtime Service Access
> Value:
> 00000000  01 00
> 
> [0] https://lore.kernel.org/u-boot/20240329071929.2461441-1-ilias.apalodimas@linaro.org/
> [1] https://arm-software.github.io/ebbr/index.html#document-chapter5-variable-storage
> 
> Changes since the RFC:
> - Return EFI_INVALID_PARAM if attributes are not volatile
> - Add EFI_WRITE_PROTECTED checks for BS, RT *only* variables
> - Add 2 EFI variables and allow userspace to write the file
> - Add selftests
> 
> Ilias Apalodimas (4):
>   efi_loader: conditionally enable SetvariableRT
>   efi_loader: Add OS notifications for SetVariableRT in RAM
>   efi_loader: add an EFI variable with the variable file contents
>   efi_selftest: add tests for setvariableRT
> 
>  include/efi_loader.h                          |   4 +
>  include/efi_variable.h                        |  15 +-
>  lib/efi_loader/Kconfig                        |  16 ++
>  lib/efi_loader/efi_boottime.c                 |   2 +
>  lib/efi_loader/efi_runtime.c                  |   1 +
>  lib/efi_loader/efi_var_common.c               |  43 ++--
>  lib/efi_loader/efi_var_file.c                 |   1 -
>  lib/efi_loader/efi_var_mem.c                  |  90 +++-----
>  lib/efi_loader/efi_variable.c                 | 210 +++++++++++++++++-
>  lib/efi_loader/efi_variable_tee.c             |   1 -
>  .../efi_selftest_variables_runtime.c          | 116 +++++++++-
>  11 files changed, 401 insertions(+), 98 deletions(-)

I can't get patch 0003 from this series to apply on master or next.