[PATCH] doc: uefi: explicitly describe manual dtb update is required

[Takahiro Akashi]

On Sat, Jun 17, 2023 at 09:58:13PM +0200, Heinrich Schuchardt wrote:
> On 6/15/23 10:03, Masahisa Kojima wrote:
> > To enforce anti-rollback to any older version, dtb must be
> > always update manually. This should be described in the
> > documentation.
> > 
> > Signed-off-by: Masahisa Kojima <masahisa.kojima at linaro.org>
> > ---
> >   doc/develop/uefi/uefi.rst | 3 +++
> >   1 file changed, 3 insertions(+)
> > 
> > diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst
> > index ffd13cebe9..d5f8c5f236 100644
> > --- a/doc/develop/uefi/uefi.rst
> > +++ b/doc/develop/uefi/uefi.rst
> > @@ -552,6 +552,9 @@ update using a capsule file with --fw-version of 5, the update will fail.
> >   When the --fw-version in the capsule file is updated, lowest-supported-version
> >   in the dtb might be updated accordingly.
> > 
> > +If user needs to enroce anti-rollback to any older version,
> > +the lowest-supported-version property in dtb must be always updated manually.
> 
> Thank you for updating the documentation.
> 
> Allowing to circumvent the rollback protection is a security issue. On a
> secure system you would probably want to disable console commands like
> mc and fdt. Shouldn't we provide an advice for safe settings?

Is there any case where a user wants to use fdt for some reason,
for example, in CONFIG_PREBOOT or CONFIG_BOOTCOMMAND?

-Takahiro Akashi

> E.g.
> 
> "If a user wanted to enable a rollback to a version forbidden by the
> lowest-supported-version property specified in U-Boot's control
> device-tree, they could change this property using the fdt command.
> Secure systems should not enable this command."
> 
> Best regards
> 
> Heinrich
> 
> > +
> >   To insert the lowest supported version into a dtb
> > 
> >   .. code-block:: console
> > 
> > base-commit: e350d0c60d413d441cbdfa9432ebadb56f625903
>