efivarfs: automatically update super block flag

efivar operation is updated when the tee_stmm_efi module is probed.
tee_stmm_efi module supports SetVariable runtime service, but user needs
to manually remount the efivarfs as RW to enable the write access if the
previous efivar operation does not support SetVariable and efivarfs is
mounted as read-only.

This commit notifies the update of efivar operation to efivarfs
subsystem, then drops SB_RDONLY flag if the efivar operation supports
SetVariable.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
[ardb: use per-superblock instance of the notifier block]
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

5 files changed, 51 insertions, 0 deletions

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 32a67c61c3b8..4fcda50acfa4 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -32,6 +32,7 @@
 #include <linux/ucs2_string.h>
 #include <linux/memblock.h>
 #include <linux/security.h>
+#include <linux/notifier.h>
 
 #include <asm/early_ioremap.h>
 
@@ -187,6 +188,9 @@ static const struct attribute_group efi_subsys_attr_group = {
 	.is_visible = efi_attr_is_visible,
 };
 
+struct blocking_notifier_head efivar_ops_nh;
+EXPORT_SYMBOL_GPL(efivar_ops_nh);
+
 static struct efivars generic_efivars;
 static struct efivar_operations generic_ops;
 
@@ -431,6 +435,8 @@ static int __init efisubsys_init(void)
 		platform_device_register_simple("efivars", 0, NULL, 0);
 	}
 
+	BLOCKING_INIT_NOTIFIER_HEAD(&efivar_ops_nh);
+
 	error = sysfs_create_group(efi_kobj, &efi_subsys_attr_group);
 	if (error) {
 		pr_err("efi: Sysfs attribute export failed with error %d.\n",
diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index e9dc7116daf1..f654e6f6af87 100644
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -63,6 +63,7 @@ int efivars_register(struct efivars *efivars,
 		     const struct efivar_operations *ops)
 {
 	int rv;
+	int event;
 
 	if (down_interruptible(&efivars_lock))
 		return -EINTR;
@@ -77,6 +78,13 @@ int efivars_register(struct efivars *efivars,
 
 	__efivars = efivars;
 
+	if (efivar_supports_writes())
+		event = EFIVAR_OPS_RDWR;
+	else
+		event = EFIVAR_OPS_RDONLY;
+
+	blocking_notifier_call_chain(&efivar_ops_nh, event, NULL);
+
 	pr_info("Registered efivars operations\n");
 	rv = 0;
 out:
diff --git a/fs/efivarfs/internal.h b/fs/efivarfs/internal.h
index 1dc0ccce3cc3..169252e6dc46 100644
--- a/fs/efivarfs/internal.h
+++ b/fs/efivarfs/internal.h
@@ -17,6 +17,8 @@ struct efivarfs_mount_opts {
 struct efivarfs_fs_info {
 	struct efivarfs_mount_opts mount_opts;
 	struct list_head efivarfs_list;
+	struct super_block *sb;
+	struct notifier_block nb;
 };
 
 struct efi_variable {
diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
index cee325b5bbdd..6038dd39367a 100644
--- a/fs/efivarfs/super.c
+++ b/fs/efivarfs/super.c
@@ -15,10 +15,30 @@
 #include <linux/slab.h>
 #include <linux/magic.h>
 #include <linux/statfs.h>
+#include <linux/notifier.h>
 #include <linux/printk.h>
 
 #include "internal.h"
 
+static int efivarfs_ops_notifier(struct notifier_block *nb, unsigned long event,
+				 void *data)
+{
+	struct efivarfs_fs_info *sfi = container_of(nb, struct efivarfs_fs_info, nb);
+
+	switch (event) {
+	case EFIVAR_OPS_RDONLY:
+		sfi->sb->s_flags |= SB_RDONLY;
+		break;
+	case EFIVAR_OPS_RDWR:
+		sfi->sb->s_flags &= ~SB_RDONLY;
+		break;
+	default:
+		return NOTIFY_DONE;
+	}
+
+	return NOTIFY_OK;
+}
+
 static void efivarfs_evict_inode(struct inode *inode)
 {
 	clear_inode(inode);
@@ -317,6 +337,12 @@ static int efivarfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	if (!root)
 		return -ENOMEM;
 
+	sfi->sb = sb;
+	sfi->nb.notifier_call = efivarfs_ops_notifier;
+	err = blocking_notifier_chain_register(&efivar_ops_nh, &sfi->nb);
+	if (err)
+		return err;
+
 	err = efivar_init(efivarfs_callback, (void *)sb, true,
 			  &sfi->efivarfs_list);
 	if (err)
@@ -371,6 +397,7 @@ static void efivarfs_kill_sb(struct super_block *sb)
 {
 	struct efivarfs_fs_info *sfi = sb->s_fs_info;
 
+	blocking_notifier_chain_unregister(&efivar_ops_nh, &sfi->nb);
 	kill_litter_super(sb);
 
 	/* Remove all entries and destroy */
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 3668aa204c47..c74f47711f0b 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1349,6 +1349,14 @@ bool efi_config_table_is_usable(const efi_guid_t *guid, unsigned long table)
 
 umode_t efi_attr_is_visible(struct kobject *kobj, struct attribute *attr, int n);
 
+/*
+ * efivar ops event type
+ */
+#define EFIVAR_OPS_RDONLY 0
+#define EFIVAR_OPS_RDWR 1
+
+extern struct blocking_notifier_head efivar_ops_nh;
+
 void efivars_generic_ops_register(void);
 void efivars_generic_ops_unregister(void);