linux-kernel - RE: Re: [PATCH v2 3/3] efi: Capsule update with user helper interface

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Date:	Fri, 6 Mar 2015 12:20:11 +0000
From:	"Kweh, Hock Leong" <hock.leong.kweh@...el.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Borislav Petkov <bp@...en8.de>,
	Matt Fleming <matt@...sole-pimps.org>,
	"Ong, Boon Leong" <boon.leong.ong@...el.com>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sam Protsenko <semen.protsenko@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ming Lei <ming.lei@...onical.com>
Subject: RE: Re: [PATCH v2 3/3] efi: Capsule update with user helper
 interface

> -----Original Message-----
> From: Andy Lutomirski [mailto:luto@...capital.net]
> Sent: Friday, March 06, 2015 7:09 AM
> 
> On Mar 5, 2015 1:19 AM, "Kweh, Hock Leong" <hock.leong.kweh@...el.com>
> wrote:
> >
> > > > This really is not a big deal. User should cope with it.
> > >
> > > No, it's a big deal, and the user should not cope.
> > >
> > > The user *should not* be required to have write access to anything in
> > > /lib to install a UEFI capsule that they download from their
> > > motherboard vendor's website.  /lib belongs to the distro, and UEFI
> > > capsules do not belong to the distro.  In this regard, UEFI capsules
> > > are completely unlike your wireless card firmware, your cpu microcode,
> > > etc.
> > >
> > > Imagine systems using NFS root, Atomic-style systems (e.g. ostree),
> > > systems that boot off squashfs, etc.  They should still be able to
> > > load capsules.  The basic user interface that should work is:
> > >
> > > # uefi-load-capsule /path/to/capsule
> > >
> > > or:
> > >
> > > # uefi-load-capsule - </path/to/capsule
> > >
> > > I don't really care how uefi-load-capsule is implemented, as long as
> > > it's straightforward, because people will screw it up if it isn't
> > > straightforward.
> > >
> > > Why is it so hard to have a file in sysfs that you write the capsule
> > > to using *cat* (not echo) and that will return an error code if cat
> > > fails?  Is it because you don't know where the end of the capsule is?
> > > if so, ioctl is designed for exactly this purpose.
> > >
> > > TBH, I find this thread kind of ridiculous.  The problem that you're
> > > trying to solve is extremely simple, the functionality that userspace
> > > needs is trivial, and all of these complex proposals for how it should
> > > work are an artifact of the fact that the kernel-internal interfaces
> > > you're using for it are not well suited to the problem at hand.
> > >
> > > --Andy
> >
> > Sorry, I may not catch your point correctly. Are you trying to tell that
> > a "normal" user can perform efi capsule update. But a "normal" user
> > does not have the right to install or copy the capsule binary into
> > "/lib/firmware/". So, there is a need to make this capsule module to
> > allow uploading the capsule binary at any path or location other than
> > "/lib/firmware/".
> >
> > Is this what you mean?
> 
> No.  Only root should be able to load capsules, but even root may not
> be able to write to /lib.
> 
> --Andy
> 

Okay, I accept that only root user can perform the load capsule. It is new
to me that root user may not have the access right to "/lib/firmware".

But I remember you do mention that CPU micro code and wifi firmware
they are different and able to write in /lib/firmware. I am curious why
efi capsule binary have such a restriction.  What is preventing it being
write to that location?

I even went to check out the FHS:
http://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard
I do not find any restriction calling out for that.

Would you mind to educate me on that?
Thanks.


Regards,
Wilson