efi: be more paranoid about available space when creating variables

commit 68d929862e29a8b52a7f2f2f86a0600423b093cd upstream.

UEFI variables are typically stored in flash. For various reasons, avaiable
space is typically not reclaimed immediately upon the deletion of a
variable - instead, the system will garbage collect during initialisation
after a reboot.

Some systems appear to handle this garbage collection extremely poorly,
failing if more than 50% of the system flash is in use. This can result in
the machine refusing to boot. The safest thing to do for the moment is to
forbid writes if they'd end up using more than half of the storage space.
We can make this more finegrained later if we come up with a method for
identifying the broken machines.

Change-Id: I2c374c5e45373a0b12e5b4fa8c7fba62b7f068e5
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
[bwh: Backported to 3.2:
 - Drop efivarfs changes and unused check_var_size()
 - Add error codes to include/linux/efi.h, added upstream by
   commit 5d9db883761a ('efi: Add support for a UEFI variable filesystem')
 - Add efi_status_to_err(), added upstream by commit 7253eaba7b17
   ('efivarfs: Return an error if we fail to read a variable')]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Rui Xiang <rui.xiang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
efivars: pstore: Do not check size when erasing variable

commit 80a19debc2f2d398cfa57fae97bc99826748a602 upstream.

In 3.2, unlike mainline, efi_pstore_erase() calls efi_pstore_write()
with a size of 0, as the underlying EFI interface treats a size of 0
as meaning deletion.

This was not taken into account in my backport of commit d80a361d779a
'efi_pstore: Check remaining space with QueryVariableInfo() before
writing data'.  The size check should be omitted when erasing.

Change-Id: I181bbc76dd28687abc09c313b3fed3cae63cd80a
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Rui Xiang <rui.xiang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
efivars: Allow disabling use as a pstore backend

commit ed9dc8ce7a1c8115dba9483a9b51df8b63a2e0ef upstream.

Add a new option, CONFIG_EFI_VARS_PSTORE, which can be set to N to
avoid using efivars as a backend to pstore, as some users may want to
compile out the code completely.

Set the default to Y to maintain backwards compatability, since this
feature has always been enabled until now.

Change-Id: I3d0d093b4399c6b579c7ede08f6520c0d6a7e374
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Cc: Josh Boyer <jwboyer@redhat.com>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Seiji Aguchi <seiji.aguchi@hds.com>
Cc: Tony Luck <tony.luck@intel.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
[xr: Backported to 3.4: adjust context]
Signed-off-by: Rui Xiang <rui.xiang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
efivars: Add module parameter to disable use as a pstore backend

commit ec0971ba5372a4dfa753f232449d23a8fd98490e upstream.

We know that with some firmware implementations writing too much data to
UEFI variables can lead to bricking machines. Recent changes attempt to
address this issue, but for some it may still be prudent to avoid
writing large amounts of data until the solution has been proven on a
wide variety of hardware.

Crash dumps or other data from pstore can potentially be a large data
source. Add a pstore_module parameter to efivars to allow disabling its
use as a backend for pstore. Also add a config option,
CONFIG_EFI_VARS_PSTORE_DEFAULT_DISABLE, to allow setting the default
value of this paramter to true (i.e. disabled by default).

Change-Id: I47e9d2969c9adcbfab256381539b44e04cc677d8
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Cc: Josh Boyer <jwboyer@redhat.com>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Seiji Aguchi <seiji.aguchi@hds.com>
Cc: Tony Luck <tony.luck@intel.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Rui Xiang <rui.xiang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>