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

Hi Greg,

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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.

What makes them more "secure" than anything else that is in sysfs today?
I didn't see anything in this patchset that provided "additional
security", did I miss it?

You're right, there's no additional security. What I should have said
was that I didn't think that _firmware_ variables were kernel objects in
the same way that other things in sysfs are. Having read the rest of
your reply it seems I'm mistaken on this.

I would just recommend putting this in sysfs.  Make a new subsystem
(i.e. class) and away you go.

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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.

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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.

I don't remember why efi variables were not put in sysfs, I think there
was some reasoning behind it originally.  Perhaps look in the linux-efi
archives.

I'll have a look: I suspect the appeal of efivarfs is that it allows for
things like non-case-sensitive matching on the GUID part of the filename
while retaining case-sensitivity on the part of the filename
representing the variable name.

As suggested, I'll try a sysfs class. I think that will allow me to
kill off most of the abstraction layer too. Thanks for the input.

Regards,
Daniel

thanks,

greg k-h