EFI Variables

[Emmanuel Vadot]

On Wed, 28 Oct 2015 07:27:19 +0100
Ganael Laplanche <ganael.laplanche at corp.ovh.com> wrote:

> On Tuesday, October 27, 2015 07:24:23 PM Emmanuel Vadot wrote:
> 
> Hi Emmanuel,
> 
> >   I'm currently hacking around the loader.efi
> 
> Great :)
> 
> >   I've also added the list and get command to the not working "nvram"
> > command.
> 
> I had myself posted a PR to fix that command as well as add a verbose switch 
> and the ability to specify a variable name, see :
> 
> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=202614
> 
> >   For the "set" subcommand I think that the best way to handle it is :
> >   "nvram set myvar data" -> This will set the variable myvar to data with
> > the freebsd guid (if there is any)
> > 
> >   and
> > 
> >   "nvram set myvar guid data" -> This will force the guid to <guid>
> 
> It can be useful to set variables containing *strings*, but will hardly handle 
> binary stuff :/
> 
> I am not sure whether it should be the loader's job to set variables... I can 
> think of changing the boot order, but it may be difficult to get it right by 
> hand and would probably require an upper-level tool, such as efibootmgr on 
> Linux.
> 
> >   I'll look tomorrow how to access efivars once the kernel is booted so
> > we can set some from some userland tool (especially the boot related
> > one).
> 
> Yes, this is interesting as the current kernel (amd64) does not provide access 
> to EFI variables at all.
> 
> 10.x/ia64 provided access to EFI variables through libefi(3) and io(4). It 
> should be possible to import that code to other archs too, but you'll have to 
> save the entry point to the Runtime Services Tables and maybe set a Virtual 
> Address Map too (not sure about that point).
> 
> Best regards,
> 

 The entry point for the runtime service isn't a problem, I set it as a metadata in loader.efi (this is done the same way for the graphic output protocol and efifb).
 I don't know if there is a way to call a function from it's physical addresses (doing it directly kernel panic), if not we need to set a Virtual Address Map and Convert all the addresses.

-- 
Emmanuel Vadot <manu at bidouilliste.com>