[U-Boot] [PATCH v2 00/11] efi_loader: non-volatile variables support

[Heinrich Schuchardt]

On 4/24/19 8:30 AM, AKASHI Takahiro wrote:
> This patch set is an attempt to implement non-volatile attribute for
> UEFI variables. Under the current implementation,
> * SetVariable API doesn't recognize non-volatile attribute
> * While some variables are defined non-volatile in UEFI specification,
>    they are NOT marked as non-volatile in the code.
> * env_save() (or "env save" command) allows us to save all the variables
>    into persistent storage, but it may cause volatile UEFI variables,
>    along with irrelevant U-Boot variables, to be saved unconditionally.
>
> Those observation rationalizes that the implementation of UEFI variables
> should be revamped utilizing dedicated storage for them.
>
> This patch set is yet experimental and rough-edged(See known issues below),
> but shows how UEFI variables can be split from U-Boot environment.
> This enhancement will also be vital when we introduce UEFI secure boot
> where secure and tamper-resistant storage (with authentication) is
> required.
>
> Usage:
> To enable this feature, the following configs must be enabled:
>    CONFIG_ENV_IS_IN_FAT
>    CONFIG_ENV_FAT_INTERFACE
>    CONFIG_ENV_EFI_FAT_DEVICE_AND_PART
>    CONFIG_ENV_EFI_FAT_FILE
>
> You can also define a non-volatile variable from command interface:
> => setenv -e -nv FOO baa
>
> Known issues/restriction:
> * UEFI spec defines "globally defined variables" with specific
>    attributes, but with this patch, we don't check against the user-supplied
>    attribute for any variable.
> * Only FAT can be enabled for persistent storage for UEFI non-volatile
>    variables.
> * The whole area of storage will be saved at every update of one variable.
>    It can be optimized.
> * An error during saving may cause inconsistency between cache (hash table)
>    and the storage.
> * Cache is of fixed size and can be quite big for normal usage.

Hello Takahiro,

thanks a lot for looking into persisting non-volatile UEFI variables.

Before diving into the details of the patches let us discuss the overall
design.

My understanding is that we need a buffer that lives in
EFI_RUNTIME_SERVICES_DATA and holds all variables. It is this buffer
that the operating system will access when getting or setting variables.

If a non-volatile variable is set via SetVariable() we will call a
backend driver.

Our current backend is using U-Boot environment variables. It can only
be accessed at boottime. Currently there is no guarantee that the U-Boot
variables are saved before booting. So it does not support persisting
non-volatile variables reliably.

Your patch series supplies a new backend using a file for persisting
non-volatile variables. It can only be accessed at boottime. Essentially
this solution requires no restriction to FAT file systems. We could as
well use the EXT4 driver for reading or writing the file. This file
storage is completely independent of the U-Boot environment. So it shall
not involve any changes to files env/*. I think a documentation of the
file format provided in a README would be helpful.

In case of both backends we would return EFI_UNSUPPORTED when trying to
set a non-volatile variable at runtime. Setting a volatile variable at
runtime should be allowable as long as we have sufficient space in our
buffer.

We can remove these backends based on the EVT_SIGNAL_EXIT_BOOT_SERVICES
event.

A future backend may support persisting non-volatile variables at runtime.

I would prefer if we could first introduce patches that provide the
buffer for EFI variables and link it to the UEFI variable based backend
before adding the new backend as alternative.

Best regards

Heinrich


>
> Patch#1 to #4 are preparatory so that we won't rely on U-Boot environment,
> that is, env_get/set() helper functions.
> Patch#5 to #8 are core part of changes.
> Patch#9 to #11 are for modifying variable attributes.
>
> Changes in v2 (Apr 24, 2019)
> * rebased on efi-2019-07
> * revamp the implementation
>
> v1 (Nov 28, 2018)
> * initial
>
> AKASHI Takahiro (11):
>    lib: charset: add u16_strcmp()
>    lib: charset: add u16_strncmp()
>    cmd: efidebug: rework "boot dump" sub-command using
>      GetNextVariableName()
>    efi_loader: set OsIndicationsSupported at init
>    env: save UEFI non-volatile variables in dedicated storage
>    efi_loader: variable: support non-volatile attribute
>    efi_loader: variable: split UEFI variables from U-Boot environment
>    efi_loader: load saved non-volatile variables at init
>    efi_loader: bootmgr: handle BootNext as non-volatile
>    cmd: env: add -nv option for UEFI non-volatile variable
>    cmd: efidebug: make some boot variables non-volatile
>
>   cmd/bootefi.c                     |   4 -
>   cmd/efidebug.c                    |  95 +++++++++++-----
>   cmd/nvedit.c                      |   3 +-
>   cmd/nvedit_efi.c                  |  15 ++-
>   env/Kconfig                       |  34 ++++++
>   env/env.c                         |  98 ++++++++++++++++-
>   env/fat.c                         | 109 +++++++++++++++++++
>   include/asm-generic/global_data.h |   1 +
>   include/charset.h                 |  10 ++
>   include/environment.h             |  24 +++++
>   lib/charset.c                     |  23 ++++
>   lib/efi_loader/efi_bootmgr.c      |   3 +-
>   lib/efi_loader/efi_setup.c        |  13 +++
>   lib/efi_loader/efi_variable.c     | 174 ++++++++++++++++++++++++++++--
>   14 files changed, 560 insertions(+), 46 deletions(-)
>