[PATCH 0/2] Import environment variables from FIT configuration

[Lukas Funke]

Hi Quentin,

On 02.07.2024 13:37, Quentin Schulz wrote:
> Hi Lukas,
> 
> On 7/2/24 1:01 PM, Lukas Funke wrote:
>> Hi Quentin,
>>
>> On 02.07.2024 11:16, Quentin Schulz wrote:
>>> Hi Lukas,
>>>
>>> On 7/2/24 8:48 AM, lukas.funke-oss at weidmueller.com wrote:
>>>> From: Lukas Funke <lukas.funke at weidmueller.com>
>>>>
>>>>
>>>> This series enables U-Boot to import environment variables from the
>>>> selectd FIT configuration. One use-case is that the overall build 
>>>> process
>>>> enriches the FIT configuration node with dm-verity information which
>>>> should be injected into the kernel commandline. U-Boot will then read
>>>> these (possibly signed) environment variables and put them into the
>>>> actual Kernel commandline using variable replacement
>>>> (see CONFIG_BOOTARGS_SUBST).
>>>>
>>>> Example:
>>>>
>>>> Config:
>>>> CONFIG_BOOTARGS_SUBST=y
>>>> CONFIG_ENV_IMPORT_FIT_CONF=y
>>>>
>>>> FIT:
>>>>      configurations {
>>>>          default = "conf-1";
>>>>              conf-1 {
>>>>                  kernel = "kernel-1";
>>>>                  fdt = "fdt-1";
>>>>                  env,dm-verity-args = "dm-mod.create=...";
>>>>                  env,bar = "someothervalue";
>>>>              };
>>>>      };
>>>>
>>>> U-Boot cmdline:
>>>> => env set bootargs="rootfstype=squashfs root=/dev/xyz 
>>>> ${dm-verity-args} ro"
>>>> => boot
>>>>
>>>> Kernel cmdline:
>>>> Kernel command line: rootfstype=squashfs ... dm-mod.create= ...
>>>>
>>>>
>>>
>>> I think FIT supports storing U-Boot scripts and running those via 
>>> `source` command (usually the file extension is .scr).
>>>
>>> I do not know if there's support for automatically loading this .scr 
>>> as part of a config node though, but if there isn't I guess it'd make 
>>> more sense to support this case than to come up with yet another 
>>> implementation?
>>>
>>> What do you think?
>>
>> I wasn't aware of this, thanks for pointing it out!
>>
>> This patch was mainly inspired by the dm-vertiy use-case which 
>> requires just env-variables and no (complex) scripts.
>>
>> There is currently no mechanism to source/run such scripts automatically.
>>
>> How would you distinguish between scripts that should run 
>> automatically und scripts which are sourced by a specific 
>> board/shell-script implementation? I guess there are good reasons to 
>> not run such scripts 
> 
> Scripts in conf would be automatically run? Scripts not in conf needs to 
> be executed via `source` command for example?
> 
> Not sure what to do if you want a script linked to a conf but not run 
> automatically though (and what would be the use-case?). I guess you 
> could have a script automatically run (so in conf node) that sets a 
> variable to know where to look for the other script that isn't 
> automatically executed?

Sounds like yet another level of indirection. Not sure if this a good or 
a bad thing, but makes things definitely more complicated.

> 
>> per default. I would also change current behaviour. For env variables 
>> I see no harm.
>>
> 
> If the env properties in the FIT image are part of the checksum and 
> signature of the conf node, which is necessary for secure boot, I guess 
> "no harm" fits the bill.

To my current knowledge the configuration node itself is signed. Thus, 
all env-properties are signed. Please correct me if I'm wrong.

> 
> Cheers,
> Quentin