efi: Don't use spinlocks for efi vars

All efivars operations are protected by a spinlock which prevents
interruptions and preemption. This is too restricted, we just need a
lock preventing concurrency.
The idea is to use a semaphore of count 1 and to have two ways of
locking, depending on the context:
- In interrupt context, we call down_trylock(), if it fails we return
  an error
- In normal context, we call down_interruptible()

We don't use a mutex here because the mutex_trylock() function must not
be called from interrupt context, whereas the down_trylock() can.
Signed-off-by: Sylvain Chouleur <sylvain.chouleur@intel.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Sylvain Chouleur <sylvain.chouleur@gmail.com>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>

drivers/firmware/efi/efi-pstore.c

@@ -125,16 +125,19 @@ static void efi_pstore_scan_sysfs_enter(struct efivar_entry *pos,
  * @entry: deleting entry
  * @turn_off_scanning: Check if a scanning flag should be turned off
  */
-static inline void __efi_pstore_scan_sysfs_exit(struct efivar_entry *entry,
+static inline int __efi_pstore_scan_sysfs_exit(struct efivar_entry *entry,
 						bool turn_off_scanning)
 {
 	if (entry->deleting) {
 		list_del(&entry->list);
 		efivar_entry_iter_end();
 		efivar_unregister(entry);
-		efivar_entry_iter_begin();
+		if (efivar_entry_iter_begin())
+			return -EINTR;
 	} else if (turn_off_scanning)
 		entry->scanning = false;
+
+	return 0;
 }
 
 /**
@@ -144,13 +147,18 @@ static inline void __efi_pstore_scan_sysfs_exit(struct efivar_entry *entry,
  * @head: list head
  * @stop: a flag checking if scanning will stop
  */
-static void efi_pstore_scan_sysfs_exit(struct efivar_entry *pos,
+static int efi_pstore_scan_sysfs_exit(struct efivar_entry *pos,
 				       struct efivar_entry *next,
 				       struct list_head *head, bool stop)
 {
-	__efi_pstore_scan_sysfs_exit(pos, true);
+	int ret = __efi_pstore_scan_sysfs_exit(pos, true);
+
+	if (ret)
+		return ret;
+
 	if (stop)
-		__efi_pstore_scan_sysfs_exit(next, &next->list != head);
+		ret = __efi_pstore_scan_sysfs_exit(next, &next->list != head);
+	return ret;
 }
 
 /**
@@ -172,13 +180,17 @@ static int efi_pstore_sysfs_entry_iter(void *data, struct efivar_entry **pos)
 	struct efivar_entry *entry, *n;
 	struct list_head *head = &efivar_sysfs_list;
 	int size = 0;
+	int ret;
 
 	if (!*pos) {
 		list_for_each_entry_safe(entry, n, head, list) {
 			efi_pstore_scan_sysfs_enter(entry, n, head);
 
 			size = efi_pstore_read_func(entry, data);
-			efi_pstore_scan_sysfs_exit(entry, n, head, size < 0);
+			ret = efi_pstore_scan_sysfs_exit(entry, n, head,
+							 size < 0);
+			if (ret)
+				return ret;
 			if (size)
 				break;
 		}
@@ -190,7 +202,9 @@ static int efi_pstore_sysfs_entry_iter(void *data, struct efivar_entry **pos)
 		efi_pstore_scan_sysfs_enter((*pos), n, head);
 
 		size = efi_pstore_read_func((*pos), data);
-		efi_pstore_scan_sysfs_exit((*pos), n, head, size < 0);
+		ret = efi_pstore_scan_sysfs_exit((*pos), n, head, size < 0);
+		if (ret)
+			return ret;
 		if (size)
 			break;
 	}
@@ -232,7 +246,10 @@ static ssize_t efi_pstore_read(u64 *id, enum pstore_type_id *type,
 	if (!*data.buf)
 		return -ENOMEM;
 
-	efivar_entry_iter_begin();
+	if (efivar_entry_iter_begin()) {
+		kfree(*data.buf);
+		return -EINTR;
+	}
 	size = efi_pstore_sysfs_entry_iter(&data,
 					   (struct efivar_entry **)&psi->data);
 	efivar_entry_iter_end();
@@ -347,7 +364,8 @@ static int efi_pstore_erase(enum pstore_type_id type, u64 id, int count,
 	edata.time = time;
 	edata.name = efi_name;
 
-	efivar_entry_iter_begin();
+	if (efivar_entry_iter_begin())
+		return -EINTR;
 	found = __efivar_entry_iter(efi_pstore_erase_func, &efivar_sysfs_list, &edata, &entry);
 
 	if (found && !entry->scanning) {

drivers/firmware/efi/efivars.c

@@ -510,7 +510,8 @@ static ssize_t efivar_delete(struct file *filp, struct kobject *kobj,
 		vendor = del_var->VendorGuid;
 	}
 
-	efivar_entry_iter_begin();
+	if (efivar_entry_iter_begin())
+		return -EINTR;
 	entry = efivar_entry_find(name, vendor, &efivar_sysfs_list, true);
 	if (!entry)
 		err = -EINVAL;
@@ -575,7 +576,10 @@ efivar_create_sysfs_entry(struct efivar_entry *new_var)
 		return ret;
 
 	kobject_uevent(&new_var->kobj, KOBJ_ADD);
-	efivar_entry_add(new_var, &efivar_sysfs_list);
+	if (efivar_entry_add(new_var, &efivar_sysfs_list)) {
+		efivar_unregister(new_var);
+		return -EINTR;
+	}
 
 	return 0;
 }
@@ -690,7 +694,10 @@ static int efivars_sysfs_callback(efi_char16_t *name, efi_guid_t vendor,
 
 static int efivar_sysfs_destroy(struct efivar_entry *entry, void *data)
 {
-	efivar_entry_remove(entry);
+	int err = efivar_entry_remove(entry);
+
+	if (err)
+		return err;
 	efivar_unregister(entry);
 	return 0;
 }
@@ -698,7 +705,14 @@ static int efivar_sysfs_destroy(struct efivar_entry *entry, void *data)
 static void efivars_sysfs_exit(void)
 {
 	/* Remove all entries and destroy */
-	__efivar_entry_iter(efivar_sysfs_destroy, &efivar_sysfs_list, NULL, NULL);
+	int err;
+
+	err = __efivar_entry_iter(efivar_sysfs_destroy, &efivar_sysfs_list,
+				  NULL, NULL);
+	if (err) {
+		pr_err("efivars: Failed to destroy sysfs entries\n");
+		return;
+	}
 
 	if (efivars_new_var)
 		sysfs_remove_bin_file(&efivars_kset->kobj, efivars_new_var);

drivers/firmware/efi/vars.c

@@ -43,7 +43,7 @@ static struct efivars *__efivars;
  * 2) ->ops calls
  * 3) (un)registration of __efivars
  */
-static DEFINE_SPINLOCK(efivars_lock);
+static DEFINE_SEMAPHORE(efivars_lock);
 
 static bool efivar_wq_enabled = true;
 DECLARE_WORK(efivar_work, NULL);
@@ -442,7 +442,10 @@ int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *),
 		return -ENOMEM;
 	}
 
-	spin_lock_irq(&efivars_lock);
+	if (down_interruptible(&efivars_lock)) {
+		err = -EINTR;
+		goto free;
+	}
 
 	/*
 	 * Per EFI spec, the maximum storage allocated for both
@@ -458,7 +461,7 @@ int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *),
 		switch (status) {
 		case EFI_SUCCESS:
 			if (duplicates)
-				spin_unlock_irq(&efivars_lock);
+				up(&efivars_lock);
 
 			variable_name_size = var_name_strnsize(variable_name,
 							       variable_name_size);
@@ -484,8 +487,12 @@ int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *),
 					status = EFI_NOT_FOUND;
 			}
 
-			if (duplicates)
-				spin_lock_irq(&efivars_lock);
+			if (duplicates) {
+				if (down_interruptible(&efivars_lock)) {
+					err = -EINTR;
+					goto free;
+				}
+			}
 
 			break;
 		case EFI_NOT_FOUND:
@@ -499,8 +506,8 @@ int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *),
 
 	} while (status != EFI_NOT_FOUND);
 
-	spin_unlock_irq(&efivars_lock);
-
+	up(&efivars_lock);
+free:
 	kfree(variable_name);
 
 	return err;
@@ -511,24 +518,34 @@ EXPORT_SYMBOL_GPL(efivar_init);
  * efivar_entry_add - add entry to variable list
  * @entry: entry to add to list
  * @head: list head
+ *
+ * Returns 0 on success, or a kernel error code on failure.
  */
-void efivar_entry_add(struct efivar_entry *entry, struct list_head *head)
+int efivar_entry_add(struct efivar_entry *entry, struct list_head *head)
 {
-	spin_lock_irq(&efivars_lock);
+	if (down_interruptible(&efivars_lock))
+		return -EINTR;
 	list_add(&entry->list, head);
-	spin_unlock_irq(&efivars_lock);
+	up(&efivars_lock);
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(efivar_entry_add);
 
 /**
  * efivar_entry_remove - remove entry from variable list
  * @entry: entry to remove from list
+ *
+ * Returns 0 on success, or a kernel error code on failure.
  */
-void efivar_entry_remove(struct efivar_entry *entry)
+int efivar_entry_remove(struct efivar_entry *entry)
 {
-	spin_lock_irq(&efivars_lock);
+	if (down_interruptible(&efivars_lock))
+		return -EINTR;
 	list_del(&entry->list);
-	spin_unlock_irq(&efivars_lock);
+	up(&efivars_lock);
+
+	return 0;
 }
 EXPORT_SYMBOL_GPL(efivar_entry_remove);
 
@@ -545,10 +562,8 @@ EXPORT_SYMBOL_GPL(efivar_entry_remove);
  */
 static void efivar_entry_list_del_unlock(struct efivar_entry *entry)
 {
-	lockdep_assert_held(&efivars_lock);
-
 	list_del(&entry->list);
-	spin_unlock_irq(&efivars_lock);
+	up(&efivars_lock);
 }
 
 /**
@@ -571,8 +586,6 @@ int __efivar_entry_delete(struct efivar_entry *entry)
 	const struct efivar_operations *ops = __efivars->ops;
 	efi_status_t status;
 
-	lockdep_assert_held(&efivars_lock);
-
 	status = ops->set_variable(entry->var.VariableName,
 				   &entry->var.VendorGuid,
 				   0, 0, NULL);
@@ -589,20 +602,22 @@ EXPORT_SYMBOL_GPL(__efivar_entry_delete);
  * variable list. It is the caller's responsibility to free @entry
  * once we return.
  *
- * Returns 0 on success, or a converted EFI status code if
- * set_variable() fails.
+ * Returns 0 on success, -EINTR if we can't grab the semaphore,
+ * converted EFI status code if set_variable() fails.
  */
 int efivar_entry_delete(struct efivar_entry *entry)
 {
 	const struct efivar_operations *ops = __efivars->ops;
 	efi_status_t status;
 
-	spin_lock_irq(&efivars_lock);
+	if (down_interruptible(&efivars_lock))
+		return -EINTR;
+
 	status = ops->set_variable(entry->var.VariableName,
 				   &entry->var.VendorGuid,
 				   0, 0, NULL);
 	if (!(status == EFI_SUCCESS || status == EFI_NOT_FOUND)) {
-		spin_unlock_irq(&efivars_lock);
+		up(&efivars_lock);
 		return efi_status_to_err(status);
 	}
 
@@ -628,9 +643,9 @@ EXPORT_SYMBOL_GPL(efivar_entry_delete);
  * If @head is not NULL a lookup is performed to determine whether
  * the entry is already on the list.
  *
- * Returns 0 on success, -EEXIST if a lookup is performed and the entry
- * already exists on the list, or a converted EFI status code if
- * set_variable() fails.
+ * Returns 0 on success, -EINTR if we can't grab the semaphore,
+ * -EEXIST if a lookup is performed and the entry already exists on
+ * the list, or a converted EFI status code if set_variable() fails.
  */
 int efivar_entry_set(struct efivar_entry *entry, u32 attributes,
 		     unsigned long size, void *data, struct list_head *head)
@@ -640,10 +655,10 @@ int efivar_entry_set(struct efivar_entry *entry, u32 attributes,
 	efi_char16_t *name = entry->var.VariableName;
 	efi_guid_t vendor = entry->var.VendorGuid;
 
-	spin_lock_irq(&efivars_lock);
-
+	if (down_interruptible(&efivars_lock))
+		return -EINTR;
 	if (head && efivar_entry_find(name, vendor, head, false)) {
-		spin_unlock_irq(&efivars_lock);
+		up(&efivars_lock);
 		return -EEXIST;
 	}
 
@@ -652,7 +667,7 @@ int efivar_entry_set(struct efivar_entry *entry, u32 attributes,
 		status = ops->set_variable(name, &vendor,
 					   attributes, size, data);
 
-	spin_unlock_irq(&efivars_lock);
+	up(&efivars_lock);
 
 	return efi_status_to_err(status);
 
@@ -673,23 +688,22 @@ efivar_entry_set_nonblocking(efi_char16_t *name, efi_guid_t vendor,
 			     u32 attributes, unsigned long size, void *data)
 {
 	const struct efivar_operations *ops = __efivars->ops;
-	unsigned long flags;
 	efi_status_t status;
 
-	if (!spin_trylock_irqsave(&efivars_lock, flags))
+	if (down_trylock(&efivars_lock))
 		return -EBUSY;
 
 	status = check_var_size_nonblocking(attributes,
 					    size + ucs2_strsize(name, 1024));
 	if (status != EFI_SUCCESS) {
-		spin_unlock_irqrestore(&efivars_lock, flags);
+		up(&efivars_lock);
 		return -ENOSPC;
 	}
 
 	status = ops->set_variable_nonblocking(name, &vendor, attributes,
 					       size, data);
 
-	spin_unlock_irqrestore(&efivars_lock, flags);
+	up(&efivars_lock);
 	return efi_status_to_err(status);
 }
 
@@ -714,7 +728,6 @@ int efivar_entry_set_safe(efi_char16_t *name, efi_guid_t vendor, u32 attributes,
 			  bool block, unsigned long size, void *data)
 {
 	const struct efivar_operations *ops = __efivars->ops;
-	unsigned long flags;
 	efi_status_t status;
 
 	if (!ops->query_variable_store)
@@ -735,21 +748,22 @@ int efivar_entry_set_safe(efi_char16_t *name, efi_guid_t vendor, u32 attributes,
 						    size, data);
 
 	if (!block) {
-		if (!spin_trylock_irqsave(&efivars_lock, flags))
+		if (down_trylock(&efivars_lock))
 			return -EBUSY;
 	} else {
-		spin_lock_irqsave(&efivars_lock, flags);
+		if (down_interruptible(&efivars_lock))
+			return -EINTR;
 	}
 
 	status = check_var_size(attributes, size + ucs2_strsize(name, 1024));
 	if (status != EFI_SUCCESS) {
-		spin_unlock_irqrestore(&efivars_lock, flags);
+		up(&efivars_lock);
 		return -ENOSPC;
 	}
 
 	status = ops->set_variable(name, &vendor, attributes, size, data);
 
-	spin_unlock_irqrestore(&efivars_lock, flags);
+	up(&efivars_lock);
 
 	return efi_status_to_err(status);
 }
@@ -779,8 +793,6 @@ struct efivar_entry *efivar_entry_find(efi_char16_t *name, efi_guid_t guid,
 	int strsize1, strsize2;
 	bool found = false;
 
-	lockdep_assert_held(&efivars_lock);
-
 	list_for_each_entry_safe(entry, n, head, list) {
 		strsize1 = ucs2_strsize(name, 1024);
 		strsize2 = ucs2_strsize(entry->var.VariableName, 1024);
@@ -822,10 +834,11 @@ int efivar_entry_size(struct efivar_entry *entry, unsigned long *size)
 
 	*size = 0;
 
-	spin_lock_irq(&efivars_lock);
+	if (down_interruptible(&efivars_lock))
+		return -EINTR;
 	status = ops->get_variable(entry->var.VariableName,
 				   &entry->var.VendorGuid, NULL, size, NULL);
-	spin_unlock_irq(&efivars_lock);
+	up(&efivars_lock);
 
 	if (status != EFI_BUFFER_TOO_SMALL)
 		return efi_status_to_err(status);
@@ -851,8 +864,6 @@ int __efivar_entry_get(struct efivar_entry *entry, u32 *attributes,
 	const struct efivar_operations *ops = __efivars->ops;
 	efi_status_t status;
 
-	lockdep_assert_held(&efivars_lock);
-
 	status = ops->get_variable(entry->var.VariableName,
 				   &entry->var.VendorGuid,
 				   attributes, size, data);
@@ -874,11 +885,12 @@ int efivar_entry_get(struct efivar_entry *entry, u32 *attributes,
 	const struct efivar_operations *ops = __efivars->ops;
 	efi_status_t status;
 
-	spin_lock_irq(&efivars_lock);
+	if (down_interruptible(&efivars_lock))
+		return -EINTR;
 	status = ops->get_variable(entry->var.VariableName,
 				   &entry->var.VendorGuid,
 				   attributes, size, data);
-	spin_unlock_irq(&efivars_lock);
+	up(&efivars_lock);
 
 	return efi_status_to_err(status);
 }
@@ -925,7 +937,8 @@ int efivar_entry_set_get_size(struct efivar_entry *entry, u32 attributes,
 	 * set_variable call, and removal of the variable from the efivars
 	 * list (in the case of an authenticated delete).
 	 */
-	spin_lock_irq(&efivars_lock);
+	if (down_interruptible(&efivars_lock))
+		return -EINTR;
 
 	/*
 	 * Ensure that the available space hasn't shrunk below the safe level
@@ -965,7 +978,7 @@ int efivar_entry_set_get_size(struct efivar_entry *entry, u32 attributes,
 	if (status == EFI_NOT_FOUND)
 		efivar_entry_list_del_unlock(entry);
 	else
-		spin_unlock_irq(&efivars_lock);
+		up(&efivars_lock);
 
 	if (status && status != EFI_BUFFER_TOO_SMALL)
 		return efi_status_to_err(status);
@@ -973,7 +986,7 @@ int efivar_entry_set_get_size(struct efivar_entry *entry, u32 attributes,
 	return 0;
 
 out:
-	spin_unlock_irq(&efivars_lock);
+	up(&efivars_lock);
 	return err;
 
 }
@@ -986,9 +999,9 @@ EXPORT_SYMBOL_GPL(efivar_entry_set_get_size);
  * efivar_entry_iter_end() is called. This function is usually used in
  * conjunction with __efivar_entry_iter() or efivar_entry_iter().
  */
-void efivar_entry_iter_begin(void)
+int efivar_entry_iter_begin(void)
 {
-	spin_lock_irq(&efivars_lock);
+	return down_interruptible(&efivars_lock);
 }
 EXPORT_SYMBOL_GPL(efivar_entry_iter_begin);
 
@@ -999,7 +1012,7 @@ EXPORT_SYMBOL_GPL(efivar_entry_iter_begin);
  */
 void efivar_entry_iter_end(void)
 {
-	spin_unlock_irq(&efivars_lock);
+	up(&efivars_lock);
 }
 EXPORT_SYMBOL_GPL(efivar_entry_iter_end);
 
@@ -1075,7 +1088,9 @@ int efivar_entry_iter(int (*func)(struct efivar_entry *, void *),
 {
 	int err = 0;
 
-	efivar_entry_iter_begin();
+	err = efivar_entry_iter_begin();
+	if (err)
+		return err;
 	err = __efivar_entry_iter(func, head, data, NULL);
 	efivar_entry_iter_end();
 
@@ -1120,12 +1135,17 @@ int efivars_register(struct efivars *efivars,
 		     const struct efivar_operations *ops,
 		     struct kobject *kobject)
 {
-	spin_lock_irq(&efivars_lock);
+	if (down_interruptible(&efivars_lock))
+		return -EINTR;
+
 	efivars->ops = ops;
 	efivars->kobject = kobject;
 
 	__efivars = efivars;
-	spin_unlock_irq(&efivars_lock);
+
+	pr_info("Registered efivars operations\n");
+
+	up(&efivars_lock);
 
 	return 0;
 }
@@ -1142,7 +1162,9 @@ int efivars_unregister(struct efivars *efivars)
 {
 	int rv;
 
-	spin_lock_irq(&efivars_lock);
+	if (down_interruptible(&efivars_lock))
+		return -EINTR;
+
 	if (!__efivars) {
 		printk(KERN_ERR "efivars not registered\n");
 		rv = -EINVAL;
@@ -1154,11 +1176,12 @@ int efivars_unregister(struct efivars *efivars)
 		goto out;
 	}
 
+	pr_info("Unregistered efivars operations\n");
 	__efivars = NULL;
 
 	rv = 0;
 out:
-	spin_unlock_irq(&efivars_lock);
+	up(&efivars_lock);
 	return rv;
 }
 EXPORT_SYMBOL_GPL(efivars_unregister);

fs/efivarfs/inode.c

@@ -105,7 +105,10 @@ static int efivarfs_create(struct inode *dir, struct dentry *dentry,
 
 	inode->i_private = var;
 
-	efivar_entry_add(var, &efivarfs_list);
+	err = efivar_entry_add(var, &efivarfs_list);
+	if (err)
+		goto out;
+
 	d_instantiate(dentry, inode);
 	dget(dentry);
 out:

fs/efivarfs/super.c

@@ -161,7 +161,9 @@ static int efivarfs_callback(efi_char16_t *name16, efi_guid_t vendor,
 	kfree(name);
 
 	efivar_entry_size(entry, &size);
-	efivar_entry_add(entry, &efivarfs_list);
+	err = efivar_entry_add(entry, &efivarfs_list);
+	if (err)
+		goto fail_inode;
 
 	inode_lock(inode);
 	inode->i_private = entry;
@@ -182,7 +184,10 @@ static int efivarfs_callback(efi_char16_t *name16, efi_guid_t vendor,
 
 static int efivarfs_destroy(struct efivar_entry *entry, void *data)
 {
-	efivar_entry_remove(entry);
+	int err = efivar_entry_remove(entry);
+
+	if (err)
+		return err;
 	kfree(entry);
 	return 0;
 }

include/linux/efi.h

@@ -1297,8 +1297,8 @@ struct kobject *efivars_kobject(void);
 int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *),
 		void *data, bool duplicates, struct list_head *head);
 
-void efivar_entry_add(struct efivar_entry *entry, struct list_head *head);
-void efivar_entry_remove(struct efivar_entry *entry);
+int efivar_entry_add(struct efivar_entry *entry, struct list_head *head);
+int efivar_entry_remove(struct efivar_entry *entry);
 
 int __efivar_entry_delete(struct efivar_entry *entry);
 int efivar_entry_delete(struct efivar_entry *entry);
@@ -1315,7 +1315,7 @@ int efivar_entry_set_get_size(struct efivar_entry *entry, u32 attributes,
 int efivar_entry_set_safe(efi_char16_t *name, efi_guid_t vendor, u32 attributes,
 			  bool block, unsigned long size, void *data);
 
-void efivar_entry_iter_begin(void);
+int efivar_entry_iter_begin(void);
 void efivar_entry_iter_end(void);
 
 int __efivar_entry_iter(int (*func)(struct efivar_entry *, void *),