[U-Boot] [PATCH 00/11] Introduce variables whitelisting in environment

[Simon Glass]

Hi Quentin,

On 22 December 2017 at 14:13, Quentin Schulz
<quentin.schulz at free-electrons.com> wrote:
> This patch series is based on this[1] patch series from Maxime.
>
> This is an RFC. It's been only tested in a specific use case on a custom
> i.MX6 board. It's known to break compilation on a few boards.
>
> I have a use case where we want some variables from a first environment to
> be overriden by variables from a second environment. For example, we want
> to load variables from the default env (ENV_IS_NOWHERE) and then load only
> a handful of other variables from, e.g., NAND.
>
> In our use case, we basically can be sure that the default env in the
> U-Boot binary is secure but we want only a few variables to be modified,
> thus keeping control over the overall behaviour of U-Boot in secure mode.
>
> It works in that way:
>   - from highest to lowest priority, the first environment that can be
>   loaded (that has successfully init and whose load function has returned
>   no errors) will be the main environment,
>   - then, all the following environment that could be successfully loaded
>   (same conditions as the main environment) are secondary environment. The
>   env variables that are defined both in CONFIG_ENV_VAR_WHITELIST_LIST and
>   in the secondary environments override the ones in the main environment,
>   - for saving, we save the whole environment to all environments
>   available, be they main or secondary (it does not matter to save the
>   whole environment on secondary environments as only the whitelisted
>   variables will be overriden in the loading process,
>
> I have also a few questions that could help me to get the whole thing to
> work.
>
> 1) I can't really get my head around the use of gd->env_addr, what is it used
> for? It is set in a bunch of different places but only once is it
> explicitly used (basically to alternate the env_addr between the one
> associated to main and redundant environment (in NAND for example)).
>
> 2) Why do we consider ENV_IS_NOWHERE an invalid environment? The only place I
> found a use for it was to just say that if the environment is invalid, we
> should set to default environment (in env_relocate in env/common.c). With
> my patch series I guess that we could remove this fallback and force
> ENV_IS_NOWHERE to be always there.
>
> 3) There are a few (20) boards that set gd->env_addr and gd->env_valid in
> their board file. What is the reason to do such a thing? Isn't those
> overriden anyway by the environment driver?
>
> I'm looking forward to getting your feedback on this patch series.
>

I certainly understand the goal and it seems generally useful.

But I wonder whether this is the best way to implement it.

We could have a UCLASS_ENV uclass, with driver-model drivers which
load the environment (i.e. have load() and save() methods). Config for
the drivers would come from the device tree. Useful drivers would be:

- one that loads the env from a single location
- one that loads multiple envs from different locations in priority order
- one that does what you want

Then people could set their own policy by adding a driver.

I worry that what we have here is quite heavyweight, and will be
imposed on all users, e.g. the size increase of gd, the new logic.
Where does it end? I think splitting things up into different use
cases makes sense.

When I did the env refactor I envisaged using driver-model for the
post-reloc env load/save at some point in the future. It solves the
problem of getting the config (can use device tree) and different
boards wanting to do different things (boards can provide an env
driver).

Regards,
Simon

> Thanks,
> Quentin
>
> [1] https://patchwork.ozlabs.org/cover/842057/
>
> Quentin Schulz (11):
>   env: fix ret not being set and fails when no env could have been init
>   lib: hashtable: support whitelisting env variables
>   env: add support for whitelisting variables from secondary environments
>   env: make nowhere an env medium like the others
>   cmd: saveenv: enable the saveenv command when ENV_IS_NOWHERE is defined but another env medium is enabled too
>   env: add env_driver to env_driver functions' arguments
>   env: gd flags without ENV_READY is enough to discriminate in env_get_default
>   env: add env_driver parameter to env_import_redund
>   env: make env_locations a global variable
>   env: introducing env_info struct for storing info per env
>   env: store information about each environment in gd
>
>  board/sunxi/board.c               |   2 +-
>  cmd/nvedit.c                      |  16 ++-
>  common/board_r.c                  |   8 +-
>  env/Kconfig                       |  29 +++---
>  env/common.c                      |  45 ++++++----
>  env/eeprom.c                      |  40 ++++-----
>  env/env.c                         | 142 +++++++++++++++++++++++++------
>  env/ext4.c                        |   4 +-
>  env/fat.c                         |   4 +-
>  env/flash.c                       |  58 ++++++-------
>  env/mmc.c                         |  14 +--
>  env/nand.c                        |  46 +++++-----
>  env/nowhere.c                     |  12 ++-
>  env/nvram.c                       |  18 ++--
>  env/onenand.c                     |   6 +-
>  env/remote.c                      |  10 +-
>  env/sata.c                        |   4 +-
>  env/sf.c                          |  34 +++----
>  env/ubi.c                         |  14 +--
>  include/asm-generic/global_data.h |   5 +-
>  include/environment.h             |  59 ++++++++-----
>  include/search.h                  |   2 +-
>  lib/hashtable.c                   |  17 +++-
>  23 files changed, 379 insertions(+), 210 deletions(-)
>
> base-commit: 5d41e28058e7b378c9fa5c61ecc074a682ba2db4
> --
> git-series 0.9.1