Re: [WIP RFC PATCH 0/6] Generic Firmware Variable Filesystem

[Daniel Axtens <dja@axtens.net>]

Hi Nayna,

>> As PowerNV moves towards secure boot, we need a place to put secure
>> variables. One option that has been canvassed is to make our secure
>> variables look like EFI variables. This is an early sketch of another
>> approach where we create a generic firmware variable file system,
>> fwvarfs, and an OPAL Secure Variable backend for it.
>
> Is there a need of new filesystem ? I am wondering why can't these be 
> exposed via sysfs / securityfs ?
> Probably, something like... /sys/firmware/secureboot or 
> /sys/kernel/security/secureboot/  ?

I suppose we could put secure variables in sysfs, but I'm not sure
that's what sysfs was intended for. I understand sysfs as "a
filesystem-based view of kernel objects" (from
Documentation/filesystems/configfs/configfs.txt), and I don't think a
secure variable is really a kernel object in the same way most other
things in sysfs are... but I'm open to being convinced.

securityfs seems to be reserved for LSMs, I don't think we can put
things there.

My hope with fwvarfs is to provide a generic place for firmware
variables so that we don't need to expand the list of firmware-specific
filesystems beyond efivarfs. I am also aiming to make things simple to
use so that people familiar with firmware don't also have to become
familiar with filesystem code in order to expose firmware variables to
userspace.

> Also, it sounds like this is needed only for secure firmware variables 
> and does not include
> other firmware variables which are not security relevant ? Is that 
> correct understanding ?

The primary use case at the moment - OPAL secure variables - is security
focused because the current OPAL secure variable design stores and
manipulates secure variables separately from the rest of nvram. This
isn't an inherent feature of fwvarfs.

fwvarfs can also be used for variables that are not security relevant as
well. For example, with the EFI backend (patch 3), both secure and
insecure variables can be read.

Regards,
Daniel