Re: [PATCH 5/5] efi: Make efivarfs entries immutable by default. (v5)

[Peter Jones <pjones-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Fri, Feb 12, 2016 at 02:36:28PM +0100, Laszlo Ersek wrote:
> On 02/04/16 16:34, Peter Jones wrote:
> > "rm -rf" is bricking some peoples' laptops because of variables being
> > used to store non-reinitializable firmware driver data that's required
> > to POST the hardware.
> > 
> > These are 100% bugs, and they need to be fixed, but in the mean time it
> > shouldn't be easy to *accidentally* brick machines.
> > 
> > We have to have delete working, and picking which variables do and don't
> > work for deletion is quite intractable, so instead make everything
> > immutable by default (except for a whitelist), and make tools that
> > aren't quite so broad-spectrum unset the immutable flag.
> 
> I think that the whitelist should include the following pattern
> (permitting deletion):
> - GUID:                  LINUX_EFI_CRASH_GUID
> - variable name pattern: "dump-type*"
> 
> This is because the pstore filesystem can be backed by UEFI variables,
> and (for example) a crash might dump the last kilobytes of the dmesg
> into a number of pstore entries, each entry backed by a separate UEFI
> variable in the above GUID namespace, and with a variable name according
> to the above pattern.
> 
> Please see "drivers/firmware/efi/efi-pstore.c".
> 
> While this patch series will not prevent the user from deleting those
> UEFI variables via the pstore filesystem (i.e., deleting a pstore fs
> entry will continue to delete the backing UEFI variable), I think it
> would be nice to preserve the possibility for the sysadmin to delete
> Linux-created UEFI variables that carry portions of the crash log,
> *without* having to mount the pstore filesystem.

They still have that ability with this patch - they have to chattr -i it
manually, or use libefivar's efi_del_variable() with a suitably new
libefivar, but we aren't ever actually stopping deletion.

Which doesn't mean you're wrong, mind you, but it does remove urgency.

-- 
        Peter