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Re: accessing efivarfs in debian-installer



On Fri, 2016-05-27 at 09:13 -0400, Hendrik Boom wrote:
> On Fri, May 27, 2016 at 10:59:35AM +0100, Steve McIntyre wrote:
> > On Fri, May 27, 2016 at 10:41:39AM +0200, Francesco De Vita wrote:
> > > Hi
> > > 
> > > On 25/5/2016 16:31, Cyril Brulebois wrote:
> > > > Francesco De Vita <fradev@inventati.org> (2016-05-24):
> > > > > So, is it possible to access the efivarfs interface and retrieve
> > > > > the required nvram-file inside the DI environment?
> > > > 
> > > > I'm pretty sure we can do that from d-i since that's needed to get
> > > > UEFI support working AFAICT. Looking at udebs, it seems you want to
> > > > be loading this one, probably manually if you're at an early stage:
> > > > efi-modules-4.5.0-2-amd64-di_4.5.4-1_amd64.udeb
> > > > 
> > > > It contains:
> > > >   ./lib/modules/4.5.0-2-amd64/kernel/drivers/firmware/efi/efivars.ko
> > > > 
> > > > which is likely to make it possible to access efivars, allowing you
> > > > to mount them on the mount point (which you mentioned, exists
> > > > already).
> > > 
> > > This time I'm using the Stretch Alpha 6 DI. I successfully loaded the 
> > > efivars module as you suggested, however the efivarfs interface remains 
> > > inaccessible, it still cannot be mounted.
> > > 
> > > I suppose that the efivarfs module has to be loaded too but there is no 
> > > trace of efivarfs.ko in the DI and I didn't find any udeb containing 
> > > it. Should I load it someway from an external source?
> > 
> > Ah, that's your problem. It looks like we're not including that module
> > yet. Most EFI variable users like efibootmgr will fall back to the
> > older interfaces, so we've not noticed this yet.
> > 
> > I'll go and fix that now.
> 
> Wasn't mounting the efivars as a file system implicated in the complete 
> bricking of someone's hardware a while ago?  The problem being that it 
> was too easy to rm those files, which deleted those efi variables, 
> which included variable that were essential to making booting possible?  
> Not just that it wouldn't boot the installed system any more; it could 
> no longer boot anything, not even an operating-system installer?

Fixed in Linux 4.5-rc5 and in 4.4.4.  Now only variables on a known-
safe whitelist are allowed to be deleted.

[...]
> Juat be very careful with efivars.

We are.

Ben.

-- 
Ben Hutchings
We get into the habit of living before acquiring the habit of thinking.
                                                              - Albert
Camus

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