Re: edif / create files from a grub module

[Jon McCune]

Jean-Francois,

It's possible to write one's grub.cfg to save GRUB environment variables in pre-existing GRUB environment variable files on an ext4 filesystem. What types of sanity-checking are you looking to do? It may be possible to achieve what you want with just these mechanisms.

-Jon

On Wed, May 10, 2017 at 3:13 PM, Vladimir 'phcoder' Serbinenko <address@hidden> wrote:

On Sat, Dec 10, 2016, 18:29 Andrei Borzenkov <address@hidden> wrote:

07.12.2016 00:03, Jean-Francois Le Breton пишет:
> Hello,
>      I would like to add some checks and modifications to the Linux command line
> before booting the OS.
>      So I am considering writing a grub module which will modify some grub.cfg
> parameters according to data retreived somewhere on dedicated hardware.
>       I just realized that it was not possible to write files (on EFI partition
> or EXT4 partition).
>       Is there an available patch to allow file modifications ?
>       I am using grubx64.efi + my module.

There is no write support in GRUB nor am I aware of any plans to add
one.

This is not just lack of plans. Writing to FS structures is inherently dangerous abd may result in FS corruption. So for safety reasons we reject writes to FS except in very controlled ways.

The only limited possibility is overwriting of existing file using
blocklists as long as it resides on plain device (no RAID/volume
manager/crypto/etc).

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