[PATCH] efivars: Add module parameter to allow disabling use as apstore backend

[Seth Forshee]

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_enable parameter to efivars to allow disabling its
use as a backend for pstore. Also add a config option,
CONFIG_EFI_VARS_PSTORE, which will specify the default value for this
parameter. Default this option to Y to maintain the existing behavior.

Signed-off-by: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
---
 drivers/firmware/Kconfig   |    9 ++++++
 drivers/firmware/efivars.c |   66 +++++++++++++++-----------------------------
 2 files changed, 32 insertions(+), 43 deletions(-)

diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
index 9b00072..35f7d16 100644
--- a/drivers/firmware/Kconfig
+++ b/drivers/firmware/Kconfig
@@ -53,6 +53,15 @@ config EFI_VARS
 	  Subsequent efibootmgr releases may be found at:
 	  <http://linux.dell.com/efibootmgr>
 
+config EFI_VARS_PSTORE
+	bool "Use efivars as a pstore backend"
+	depends on EFI_VARS
+	default y
+	help
+	  Say Y here to enable the use of efivars as a storage backend
+	  for pstore. This setting can be overridden using the
+	  efivars.pstore_enable 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 fe62aa3..1e5d326 100644
--- a/drivers/firmware/efivars.c
+++ b/drivers/firmware/efivars.c
@@ -103,6 +103,9 @@ MODULE_VERSION(EFIVARS_VERSION);
  */
 #define GUID_LEN 36
 
+static bool efivars_pstore_enable = IS_ENABLED(CONFIG_EFI_VARS_PSTORE);
+module_param_named(pstore_enable, efivars_pstore_enable, bool, 0644);
+
 /*
  * The maximum size of VariableName + Data = 1024
  * Therefore, it's reasonable to save that much
@@ -1309,8 +1312,6 @@ static const struct inode_operations efivarfs_dir_inode_operations = {
 	.create = efivarfs_create,
 };
 
-static struct pstore_info efi_pstore_info;
-
 #ifdef CONFIG_PSTORE
 
 static int efi_pstore_open(struct pstore_info *psi)
@@ -1514,38 +1515,6 @@ static int efi_pstore_erase(enum pstore_type_id type, u64 id, int count,
 
 	return 0;
 }
-#else
-static int efi_pstore_open(struct pstore_info *psi)
-{
-	return 0;
-}
-
-static int efi_pstore_close(struct pstore_info *psi)
-{
-	return 0;
-}
-
-static ssize_t efi_pstore_read(u64 *id, enum pstore_type_id *type, int *count,
-			       struct timespec *timespec,
-			       char **buf, struct pstore_info *psi)
-{
-	return -1;
-}
-
-static int efi_pstore_write(enum pstore_type_id type,
-		enum kmsg_dump_reason reason, u64 *id,
-		unsigned int part, int count, size_t size,
-		struct pstore_info *psi)
-{
-	return 0;
-}
-
-static int efi_pstore_erase(enum pstore_type_id type, u64 id, int count,
-			    struct timespec time, struct pstore_info *psi)
-{
-	return 0;
-}
-#endif
 
 static struct pstore_info efi_pstore_info = {
 	.owner		= THIS_MODULE,
@@ -1557,6 +1526,24 @@ static struct pstore_info efi_pstore_info = {
 	.erase		= efi_pstore_erase,
 };
 
+static void efivar_pstore_register(struct efivars *efivars)
+{
+	efivars->efi_pstore_info = efi_pstore_info;
+	efivars->efi_pstore_info.buf = kmalloc(4096, GFP_KERNEL);
+	if (efivars->efi_pstore_info.buf) {
+		efivars->efi_pstore_info.bufsize = 1024;
+		efivars->efi_pstore_info.data = efivars;
+		spin_lock_init(&efivars->efi_pstore_info.buf_lock);
+		pstore_register(&efivars->efi_pstore_info);
+	}
+}
+#else
+static void efivar_pstore_register(struct efivars *efivars)
+{
+	return;
+}
+#endif
+
 static ssize_t efivar_create(struct file *filp, struct kobject *kobj,
 			     struct bin_attribute *bin_attr,
 			     char *buf, loff_t pos, size_t count)
@@ -2025,15 +2012,8 @@ int register_efivars(struct efivars *efivars,
 	if (error)
 		unregister_efivars(efivars);
 
-	efivars->efi_pstore_info = efi_pstore_info;
-
-	efivars->efi_pstore_info.buf = kmalloc(4096, GFP_KERNEL);
-	if (efivars->efi_pstore_info.buf) {
-		efivars->efi_pstore_info.bufsize = 1024;
-		efivars->efi_pstore_info.data = efivars;
-		spin_lock_init(&efivars->efi_pstore_info.buf_lock);
-		pstore_register(&efivars->efi_pstore_info);
-	}
+	if (efivars_pstore_enable)
+		efivar_pstore_register(efivars);
 
 	register_filesystem(&efivarfs_type);
 
-- 
1.7.9.5

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