[ 3.5.y.z extended stable ] Patch "efivars: Add module parameter to disable use as a pstore" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    efivars: Add module parameter to disable use as a pstore

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From e22696ebbb2049b6372e386cb0b642fd04782cc7 Mon Sep 17 00:00:00 2001
From: Seth Forshee <seth.forshee at canonical.com>
Date: Mon, 11 Mar 2013 16:17:50 -0500
Subject: [PATCH] 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).

Signed-off-by: Seth Forshee <seth.forshee at canonical.com>
Cc: Josh Boyer <jwboyer at redhat.com>
Cc: Matthew Garrett <mjg59 at srcf.ucam.org>
Cc: Seiji Aguchi <seiji.aguchi at hds.com>
Cc: Tony Luck <tony.luck at intel.com>
Signed-off-by: Matt Fleming <matt.fleming at intel.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/firmware/Kconfig   | 9 +++++++++
 drivers/firmware/efivars.c | 8 +++++++-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
index 898023d..42c759a 100644
--- a/drivers/firmware/Kconfig
+++ b/drivers/firmware/Kconfig
@@ -62,6 +62,15 @@ config EFI_VARS_PSTORE
 	  will allow writing console messages, crash dumps, or anything
 	  else supported by pstore to EFI variables.

+config EFI_VARS_PSTORE_DEFAULT_DISABLE
+	bool "Disable using efivars as a pstore backend by default"
+	depends on EFI_VARS_PSTORE
+	default n
+	help
+	  Saying Y here will disable the use of efivars as a storage
+	  backend for pstore by default. This setting can be overridden
+	  using the efivars module's pstore_disable parameter.
+
 config EFI_PCDP
 	bool "Console device selection via EFI PCDP or HCDP table"
 	depends on ACPI && EFI && IA64
diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index 40d4e03..af8fec1 100644
--- a/drivers/firmware/efivars.c
+++ b/drivers/firmware/efivars.c
@@ -92,6 +92,11 @@ MODULE_VERSION(EFIVARS_VERSION);

 #define DUMP_NAME_LEN 52

+static bool efivars_pstore_disable =
+	IS_ENABLED(EFI_VARS_PSTORE_DEFAULT_DISABLE);
+
+module_param_named(pstore_disable, efivars_pstore_disable, bool, 0644);
+
 /*
  * The maximum size of VariableName + Data = 1024
  * Therefore, it's reasonable to save that much
@@ -1173,7 +1178,8 @@ int register_efivars(struct efivars *efivars,
 	if (error)
 		unregister_efivars(efivars);

-	efivar_pstore_register(efivars);
+	if (!efivars_pstore_disable)
+		efivar_pstore_register(efivars);

 out:
 	kfree(variable_name);
--
1.8.1.2