efi: Add nonblocking option to efi_query_variable_store()

[mirror_ubuntu-bionic-kernel.git] / drivers / firmware / efi / vars.c

/*
 * Originally from efivars.c
 *
 * Copyright (C) 2001,2003,2004 Dell <Matt_Domsch@dell.com>
 * Copyright (C) 2004 Intel Corporation <matthew.e.tolentino@intel.com>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <linux/capability.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/string.h>
#include <linux/smp.h>
#include <linux/efi.h>
#include <linux/sysfs.h>
#include <linux/device.h>
#include <linux/slab.h>
#include <linux/ctype.h>
#include <linux/ucs2_string.h>

/* Private pointer to registered efivars */
static struct efivars *__efivars;

static bool efivar_wq_enabled = true;
DECLARE_WORK(efivar_work, NULL);
EXPORT_SYMBOL_GPL(efivar_work);

static bool
validate_device_path(efi_char16_t *var_name, int match, u8 *buffer,
                     unsigned long len)
{
        struct efi_generic_dev_path *node;
        int offset = 0;

        node = (struct efi_generic_dev_path *)buffer;

        if (len < sizeof(*node))
                return false;

        while (offset <= len - sizeof(*node) &&
               node->length >= sizeof(*node) &&
                node->length <= len - offset) {
                offset += node->length;

                if ((node->type == EFI_DEV_END_PATH ||
                     node->type == EFI_DEV_END_PATH2) &&
                    node->sub_type == EFI_DEV_END_ENTIRE)
                        return true;

                node = (struct efi_generic_dev_path *)(buffer + offset);
        }

        /*
         * If we're here then either node->length pointed past the end
         * of the buffer or we reached the end of the buffer without
         * finding a device path end node.
         */
        return false;
}

static bool
validate_boot_order(efi_char16_t *var_name, int match, u8 *buffer,
                    unsigned long len)
{
        /* An array of 16-bit integers */
        if ((len % 2) != 0)
                return false;

        return true;
}

static bool
validate_load_option(efi_char16_t *var_name, int match, u8 *buffer,
                     unsigned long len)
{
        u16 filepathlength;
        int i, desclength = 0, namelen;

        namelen = ucs2_strnlen(var_name, EFI_VAR_NAME_LEN);

        /* Either "Boot" or "Driver" followed by four digits of hex */
        for (i = match; i < match+4; i++) {
                if (var_name[i] > 127 ||
                    hex_to_bin(var_name[i] & 0xff) < 0)
                        return true;
        }

        /* Reject it if there's 4 digits of hex and then further content */
        if (namelen > match + 4)
                return false;

        /* A valid entry must be at least 8 bytes */
        if (len < 8)
                return false;

        filepathlength = buffer[4] | buffer[5] << 8;

        /*
         * There's no stored length for the description, so it has to be
         * found by hand
         */
        desclength = ucs2_strsize((efi_char16_t *)(buffer + 6), len - 6) + 2;

        /* Each boot entry must have a descriptor */
        if (!desclength)
                return false;

        /*
         * If the sum of the length of the description, the claimed filepath
         * length and the original header are greater than the length of the
         * variable, it's malformed
         */
        if ((desclength + filepathlength + 6) > len)
                return false;

        /*
         * And, finally, check the filepath
         */
        return validate_device_path(var_name, match, buffer + desclength + 6,
                                    filepathlength);
}

static bool
validate_uint16(efi_char16_t *var_name, int match, u8 *buffer,
                unsigned long len)
{
        /* A single 16-bit integer */
        if (len != 2)
                return false;

        return true;
}

static bool
validate_ascii_string(efi_char16_t *var_name, int match, u8 *buffer,
                      unsigned long len)
{
        int i;

        for (i = 0; i < len; i++) {
                if (buffer[i] > 127)
                        return false;

                if (buffer[i] == 0)
                        return true;
        }

        return false;
}

struct variable_validate {
        char *name;
        bool (*validate)(efi_char16_t *var_name, int match, u8 *data,
                         unsigned long len);
};

static const struct variable_validate variable_validate[] = {
        { "BootNext", validate_uint16 },
        { "BootOrder", validate_boot_order },
        { "DriverOrder", validate_boot_order },
        { "Boot*", validate_load_option },
        { "Driver*", validate_load_option },
        { "ConIn", validate_device_path },
        { "ConInDev", validate_device_path },
        { "ConOut", validate_device_path },
        { "ConOutDev", validate_device_path },
        { "ErrOut", validate_device_path },
        { "ErrOutDev", validate_device_path },
        { "Timeout", validate_uint16 },
        { "Lang", validate_ascii_string },
        { "PlatformLang", validate_ascii_string },
        { "", NULL },
};

bool
efivar_validate(efi_char16_t *var_name, u8 *data, unsigned long len)
{
        int i;
        u16 *unicode_name = var_name;

        for (i = 0; variable_validate[i].validate != NULL; i++) {
                const char *name = variable_validate[i].name;
                int match;

                for (match = 0; ; match++) {
                        char c = name[match];
                        u16 u = unicode_name[match];

                        /* All special variables are plain ascii */
                        if (u > 127)
                                return true;

                        /* Wildcard in the matching name means we've matched */
                        if (c == '*')
                                return variable_validate[i].validate(var_name,
                                                             match, data, len);

                        /* Case sensitive match */
                        if (c != u)
                                break;

                        /* Reached the end of the string while matching */
                        if (!c)
                                return variable_validate[i].validate(var_name,
                                                             match, data, len);
                }
        }

        return true;
}
EXPORT_SYMBOL_GPL(efivar_validate);

static efi_status_t
check_var_size(u32 attributes, unsigned long size)
{
        const struct efivar_operations *fops = __efivars->ops;

        if (!fops->query_variable_store)
                return EFI_UNSUPPORTED;

        return fops->query_variable_store(attributes, size, false);
}

static efi_status_t
check_var_size_nonblocking(u32 attributes, unsigned long size)
{
        const struct efivar_operations *fops = __efivars->ops;

        if (!fops->query_variable_store)
                return EFI_UNSUPPORTED;

        return fops->query_variable_store(attributes, size, true);
}

static int efi_status_to_err(efi_status_t status)
{
        int err;

        switch (status) {
        case EFI_SUCCESS:
                err = 0;
                break;
        case EFI_INVALID_PARAMETER:
                err = -EINVAL;
                break;
        case EFI_OUT_OF_RESOURCES:
                err = -ENOSPC;
                break;
        case EFI_DEVICE_ERROR:
                err = -EIO;
                break;
        case EFI_WRITE_PROTECTED:
                err = -EROFS;
                break;
        case EFI_SECURITY_VIOLATION:
                err = -EACCES;
                break;
        case EFI_NOT_FOUND:
                err = -ENOENT;
                break;
        default:
                err = -EINVAL;
        }

        return err;
}

static bool variable_is_present(efi_char16_t *variable_name, efi_guid_t *vendor,
                                struct list_head *head)
{
        struct efivar_entry *entry, *n;
        unsigned long strsize1, strsize2;
        bool found = false;

        strsize1 = ucs2_strsize(variable_name, 1024);
        list_for_each_entry_safe(entry, n, head, list) {
                strsize2 = ucs2_strsize(entry->var.VariableName, 1024);
                if (strsize1 == strsize2 &&
                        !memcmp(variable_name, &(entry->var.VariableName),
                                strsize2) &&
                        !efi_guidcmp(entry->var.VendorGuid,
                                *vendor)) {
                        found = true;
                        break;
                }
        }
        return found;
}

/*
 * Returns the size of variable_name, in bytes, including the
 * terminating NULL character, or variable_name_size if no NULL
 * character is found among the first variable_name_size bytes.
 */
static unsigned long var_name_strnsize(efi_char16_t *variable_name,
                                       unsigned long variable_name_size)
{
        unsigned long len;
        efi_char16_t c;

        /*
         * The variable name is, by definition, a NULL-terminated
         * string, so make absolutely sure that variable_name_size is
         * the value we expect it to be. If not, return the real size.
         */
        for (len = 2; len <= variable_name_size; len += sizeof(c)) {
                c = variable_name[(len / sizeof(c)) - 1];
                if (!c)
                        break;
        }

        return min(len, variable_name_size);
}

/*
 * Print a warning when duplicate EFI variables are encountered and
 * disable the sysfs workqueue since the firmware is buggy.
 */
static void dup_variable_bug(efi_char16_t *str16, efi_guid_t *vendor_guid,
                             unsigned long len16)
{
        size_t i, len8 = len16 / sizeof(efi_char16_t);
        char *str8;

        /*
         * Disable the workqueue since the algorithm it uses for
         * detecting new variables won't work with this buggy
         * implementation of GetNextVariableName().
         */
        efivar_wq_enabled = false;

        str8 = kzalloc(len8, GFP_KERNEL);
        if (!str8)
                return;

        for (i = 0; i < len8; i++)
                str8[i] = str16[i];

        printk(KERN_WARNING "efivars: duplicate variable: %s-%pUl\n",
               str8, vendor_guid);
        kfree(str8);
}

/**
 * efivar_init - build the initial list of EFI variables
 * @func: callback function to invoke for every variable
 * @data: function-specific data to pass to @func
 * @atomic: do we need to execute the @func-loop atomically?
 * @duplicates: error if we encounter duplicates on @head?
 * @head: initialised head of variable list
 *
 * Get every EFI variable from the firmware and invoke @func. @func
 * should call efivar_entry_add() to build the list of variables.
 *
 * Returns 0 on success, or a kernel error code on failure.
 */
int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *),
                void *data, bool atomic, bool duplicates,
                struct list_head *head)
{
        const struct efivar_operations *ops = __efivars->ops;
        unsigned long variable_name_size = 1024;
        efi_char16_t *variable_name;
        efi_status_t status;
        efi_guid_t vendor_guid;
        int err = 0;

        variable_name = kzalloc(variable_name_size, GFP_KERNEL);
        if (!variable_name) {
                printk(KERN_ERR "efivars: Memory allocation failed.\n");
                return -ENOMEM;
        }

        spin_lock_irq(&__efivars->lock);

        /*
         * Per EFI spec, the maximum storage allocated for both
         * the variable name and variable data is 1024 bytes.
         */

        do {
                variable_name_size = 1024;

                status = ops->get_next_variable(&variable_name_size,
                                                variable_name,
                                                &vendor_guid);
                switch (status) {
                case EFI_SUCCESS:
                        if (!atomic)
                                spin_unlock_irq(&__efivars->lock);

                        variable_name_size = var_name_strnsize(variable_name,
                                                               variable_name_size);

                        /*
                         * Some firmware implementations return the
                         * same variable name on multiple calls to
                         * get_next_variable(). Terminate the loop
                         * immediately as there is no guarantee that
                         * we'll ever see a different variable name,
                         * and may end up looping here forever.
                         */
                        if (duplicates &&
                            variable_is_present(variable_name, &vendor_guid, head)) {
                                dup_variable_bug(variable_name, &vendor_guid,
                                                 variable_name_size);
                                if (!atomic)
                                        spin_lock_irq(&__efivars->lock);

                                status = EFI_NOT_FOUND;
                                break;
                        }

                        err = func(variable_name, vendor_guid, variable_name_size, data);
                        if (err)
                                status = EFI_NOT_FOUND;

                        if (!atomic)
                                spin_lock_irq(&__efivars->lock);

                        break;
                case EFI_NOT_FOUND:
                        break;
                default:
                        printk(KERN_WARNING "efivars: get_next_variable: status=%lx\n",
                                status);
                        status = EFI_NOT_FOUND;
                        break;
                }

        } while (status != EFI_NOT_FOUND);

        spin_unlock_irq(&__efivars->lock);

        kfree(variable_name);

        return err;
}
EXPORT_SYMBOL_GPL(efivar_init);

/**
 * efivar_entry_add - add entry to variable list
 * @entry: entry to add to list
 * @head: list head
 */
void efivar_entry_add(struct efivar_entry *entry, struct list_head *head)
{
        spin_lock_irq(&__efivars->lock);
        list_add(&entry->list, head);
        spin_unlock_irq(&__efivars->lock);
}
EXPORT_SYMBOL_GPL(efivar_entry_add);

/**
 * efivar_entry_remove - remove entry from variable list
 * @entry: entry to remove from list
 */
void efivar_entry_remove(struct efivar_entry *entry)
{
        spin_lock_irq(&__efivars->lock);
        list_del(&entry->list);
        spin_unlock_irq(&__efivars->lock);
}
EXPORT_SYMBOL_GPL(efivar_entry_remove);

/*
 * efivar_entry_list_del_unlock - remove entry from variable list
 * @entry: entry to remove
 *
 * Remove @entry from the variable list and release the list lock.
 *
 * NOTE: slightly weird locking semantics here - we expect to be
 * called with the efivars lock already held, and we release it before
 * returning. This is because this function is usually called after
 * set_variable() while the lock is still held.
 */
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);
}

/**
 * __efivar_entry_delete - delete an EFI variable
 * @entry: entry containing EFI variable to delete
 *
 * Delete the variable from the firmware but leave @entry on the
 * variable list.
 *
 * This function differs from efivar_entry_delete() because it does
 * not remove @entry from the variable list. Also, it is safe to be
 * called from within a efivar_entry_iter_begin() and
 * efivar_entry_iter_end() region, unlike efivar_entry_delete().
 *
 * Returns 0 on success, or a 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;

        lockdep_assert_held(&__efivars->lock);

        status = ops->set_variable(entry->var.VariableName,
                                   &entry->var.VendorGuid,
                                   0, 0, NULL);

        return efi_status_to_err(status);
}
EXPORT_SYMBOL_GPL(__efivar_entry_delete);

/**
 * efivar_entry_delete - delete variable and remove entry from list
 * @entry: entry containing variable to delete
 *
 * Delete the variable from the firmware and remove @entry from the
 * 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.
 */
int efivar_entry_delete(struct efivar_entry *entry)
{
        const struct efivar_operations *ops = __efivars->ops;
        efi_status_t status;

        spin_lock_irq(&__efivars->lock);
        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);
                return efi_status_to_err(status);
        }

        efivar_entry_list_del_unlock(entry);
        return 0;
}
EXPORT_SYMBOL_GPL(efivar_entry_delete);

/**
 * efivar_entry_set - call set_variable()
 * @entry: entry containing the EFI variable to write
 * @attributes: variable attributes
 * @size: size of @data buffer
 * @data: buffer containing variable data
 * @head: head of variable list
 *
 * Calls set_variable() for an EFI variable. If creating a new EFI
 * variable, this function is usually followed by efivar_entry_add().
 *
 * Before writing the variable, the remaining EFI variable storage
 * space is checked to ensure there is enough room available.
 *
 * 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.
 */
int efivar_entry_set(struct efivar_entry *entry, u32 attributes,
                     unsigned long size, void *data, struct list_head *head)
{
        const struct efivar_operations *ops = __efivars->ops;
        efi_status_t status;
        efi_char16_t *name = entry->var.VariableName;
        efi_guid_t vendor = entry->var.VendorGuid;

        spin_lock_irq(&__efivars->lock);

        if (head && efivar_entry_find(name, vendor, head, false)) {
                spin_unlock_irq(&__efivars->lock);
                return -EEXIST;
        }

        status = check_var_size(attributes, size + ucs2_strsize(name, 1024));
        if (status == EFI_SUCCESS || status == EFI_UNSUPPORTED)
                status = ops->set_variable(name, &vendor,
                                           attributes, size, data);

        spin_unlock_irq(&__efivars->lock);

        return efi_status_to_err(status);

}
EXPORT_SYMBOL_GPL(efivar_entry_set);

/*
 * efivar_entry_set_nonblocking - call set_variable_nonblocking()
 *
 * This function is guaranteed to not block and is suitable for calling
 * from crash/panic handlers.
 *
 * Crucially, this function will not block if it cannot acquire
 * __efivars->lock. Instead, it returns -EBUSY.
 */
static int
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))
                return -EBUSY;

        status = check_var_size_nonblocking(attributes,
                                            size + ucs2_strsize(name, 1024));
        if (status != EFI_SUCCESS) {
                spin_unlock_irqrestore(&__efivars->lock, flags);
                return -ENOSPC;
        }

        status = ops->set_variable_nonblocking(name, &vendor, attributes,
                                               size, data);

        spin_unlock_irqrestore(&__efivars->lock, flags);
        return efi_status_to_err(status);
}

/**
 * efivar_entry_set_safe - call set_variable() if enough space in firmware
 * @name: buffer containing the variable name
 * @vendor: variable vendor guid
 * @attributes: variable attributes
 * @block: can we block in this context?
 * @size: size of @data buffer
 * @data: buffer containing variable data
 *
 * Ensures there is enough free storage in the firmware for this variable, and
 * if so, calls set_variable(). If creating a new EFI variable, this function
 * is usually followed by efivar_entry_add().
 *
 * Returns 0 on success, -ENOSPC if the firmware does not have enough
 * space for set_variable() to succeed, or a converted EFI status code
 * if set_variable() fails.
 */
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)
                return -ENOSYS;

        /*
         * If the EFI variable backend provides a non-blocking
         * ->set_variable() operation and we're in a context where we
         * cannot block, then we need to use it to avoid live-locks,
         * since the implication is that the regular ->set_variable()
         * will block.
         *
         * If no ->set_variable_nonblocking() is provided then
         * ->set_variable() is assumed to be non-blocking.
         */
        if (!block && ops->set_variable_nonblocking)
                return efivar_entry_set_nonblocking(name, vendor, attributes,
                                                    size, data);

        if (!block) {
                if (!spin_trylock_irqsave(&__efivars->lock, flags))
                        return -EBUSY;
        } else {
                spin_lock_irqsave(&__efivars->lock, flags);
        }

        status = check_var_size(attributes, size + ucs2_strsize(name, 1024));
        if (status != EFI_SUCCESS) {
                spin_unlock_irqrestore(&__efivars->lock, flags);
                return -ENOSPC;
        }

        status = ops->set_variable(name, &vendor, attributes, size, data);

        spin_unlock_irqrestore(&__efivars->lock, flags);

        return efi_status_to_err(status);
}
EXPORT_SYMBOL_GPL(efivar_entry_set_safe);

/**
 * efivar_entry_find - search for an entry
 * @name: the EFI variable name
 * @guid: the EFI variable vendor's guid
 * @head: head of the variable list
 * @remove: should we remove the entry from the list?
 *
 * Search for an entry on the variable list that has the EFI variable
 * name @name and vendor guid @guid. If an entry is found on the list
 * and @remove is true, the entry is removed from the list.
 *
 * The caller MUST call efivar_entry_iter_begin() and
 * efivar_entry_iter_end() before and after the invocation of this
 * function, respectively.
 *
 * Returns the entry if found on the list, %NULL otherwise.
 */
struct efivar_entry *efivar_entry_find(efi_char16_t *name, efi_guid_t guid,
                                       struct list_head *head, bool remove)
{
        struct efivar_entry *entry, *n;
        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);
                if (strsize1 == strsize2 &&
                    !memcmp(name, &(entry->var.VariableName), strsize1) &&
                    !efi_guidcmp(guid, entry->var.VendorGuid)) {
                        found = true;
                        break;
                }
        }

        if (!found)
                return NULL;

        if (remove) {
                if (entry->scanning) {
                        /*
                         * The entry will be deleted
                         * after scanning is completed.
                         */
                        entry->deleting = true;
                } else
                        list_del(&entry->list);
        }

        return entry;
}
EXPORT_SYMBOL_GPL(efivar_entry_find);

/**
 * efivar_entry_size - obtain the size of a variable
 * @entry: entry for this variable
 * @size: location to store the variable's size
 */
int efivar_entry_size(struct efivar_entry *entry, unsigned long *size)
{
        const struct efivar_operations *ops = __efivars->ops;
        efi_status_t status;

        *size = 0;

        spin_lock_irq(&__efivars->lock);
        status = ops->get_variable(entry->var.VariableName,
                                   &entry->var.VendorGuid, NULL, size, NULL);
        spin_unlock_irq(&__efivars->lock);

        if (status != EFI_BUFFER_TOO_SMALL)
                return efi_status_to_err(status);

        return 0;
}
EXPORT_SYMBOL_GPL(efivar_entry_size);

/**
 * __efivar_entry_get - call get_variable()
 * @entry: read data for this variable
 * @attributes: variable attributes
 * @size: size of @data buffer
 * @data: buffer to store variable data
 *
 * The caller MUST call efivar_entry_iter_begin() and
 * efivar_entry_iter_end() before and after the invocation of this
 * function, respectively.
 */
int __efivar_entry_get(struct efivar_entry *entry, u32 *attributes,
                       unsigned long *size, void *data)
{
        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);

        return efi_status_to_err(status);
}
EXPORT_SYMBOL_GPL(__efivar_entry_get);

/**
 * efivar_entry_get - call get_variable()
 * @entry: read data for this variable
 * @attributes: variable attributes
 * @size: size of @data buffer
 * @data: buffer to store variable data
 */
int efivar_entry_get(struct efivar_entry *entry, u32 *attributes,
                     unsigned long *size, void *data)
{
        const struct efivar_operations *ops = __efivars->ops;
        efi_status_t status;

        spin_lock_irq(&__efivars->lock);
        status = ops->get_variable(entry->var.VariableName,
                                   &entry->var.VendorGuid,
                                   attributes, size, data);
        spin_unlock_irq(&__efivars->lock);

        return efi_status_to_err(status);
}
EXPORT_SYMBOL_GPL(efivar_entry_get);

/**
 * efivar_entry_set_get_size - call set_variable() and get new size (atomic)
 * @entry: entry containing variable to set and get
 * @attributes: attributes of variable to be written
 * @size: size of data buffer
 * @data: buffer containing data to write
 * @set: did the set_variable() call succeed?
 *
 * This is a pretty special (complex) function. See efivarfs_file_write().
 *
 * Atomically call set_variable() for @entry and if the call is
 * successful, return the new size of the variable from get_variable()
 * in @size. The success of set_variable() is indicated by @set.
 *
 * Returns 0 on success, -EINVAL if the variable data is invalid,
 * -ENOSPC if the firmware does not have enough available space, or a
 * converted EFI status code if either of set_variable() or
 * get_variable() fail.
 *
 * If the EFI variable does not exist when calling set_variable()
 * (EFI_NOT_FOUND), @entry is removed from the variable list.
 */
int efivar_entry_set_get_size(struct efivar_entry *entry, u32 attributes,
                              unsigned long *size, void *data, bool *set)
{
        const struct efivar_operations *ops = __efivars->ops;
        efi_char16_t *name = entry->var.VariableName;
        efi_guid_t *vendor = &entry->var.VendorGuid;
        efi_status_t status;
        int err;

        *set = false;

        if (efivar_validate(name, data, *size) == false)
                return -EINVAL;

        /*
         * The lock here protects the get_variable call, the conditional
         * set_variable call, and removal of the variable from the efivars
         * list (in the case of an authenticated delete).
         */
        spin_lock_irq(&__efivars->lock);

        /*
         * Ensure that the available space hasn't shrunk below the safe level
         */
        status = check_var_size(attributes, *size + ucs2_strsize(name, 1024));
        if (status != EFI_SUCCESS) {
                if (status != EFI_UNSUPPORTED) {
                        err = efi_status_to_err(status);
                        goto out;
                }

                if (*size > 65536) {
                        err = -ENOSPC;
                        goto out;
                }
        }

        status = ops->set_variable(name, vendor, attributes, *size, data);
        if (status != EFI_SUCCESS) {
                err = efi_status_to_err(status);
                goto out;
        }

        *set = true;

        /*
         * Writing to the variable may have caused a change in size (which
         * could either be an append or an overwrite), or the variable to be
         * deleted. Perform a GetVariable() so we can tell what actually
         * happened.
         */
        *size = 0;
        status = ops->get_variable(entry->var.VariableName,
                                   &entry->var.VendorGuid,
                                   NULL, size, NULL);

        if (status == EFI_NOT_FOUND)
                efivar_entry_list_del_unlock(entry);
        else
                spin_unlock_irq(&__efivars->lock);

        if (status && status != EFI_BUFFER_TOO_SMALL)
                return efi_status_to_err(status);

        return 0;

out:
        spin_unlock_irq(&__efivars->lock);
        return err;

}
EXPORT_SYMBOL_GPL(efivar_entry_set_get_size);

/**
 * efivar_entry_iter_begin - begin iterating the variable list
 *
 * Lock the variable list to prevent entry insertion and removal until
 * 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)
{
        spin_lock_irq(&__efivars->lock);
}
EXPORT_SYMBOL_GPL(efivar_entry_iter_begin);

/**
 * efivar_entry_iter_end - finish iterating the variable list
 *
 * Unlock the variable list and allow modifications to the list again.
 */
void efivar_entry_iter_end(void)
{
        spin_unlock_irq(&__efivars->lock);
}
EXPORT_SYMBOL_GPL(efivar_entry_iter_end);

/**
 * __efivar_entry_iter - iterate over variable list
 * @func: callback function
 * @head: head of the variable list
 * @data: function-specific data to pass to callback
 * @prev: entry to begin iterating from
 *
 * Iterate over the list of EFI variables and call @func with every
 * entry on the list. It is safe for @func to remove entries in the
 * list via efivar_entry_delete().
 *
 * You MUST call efivar_enter_iter_begin() before this function, and
 * efivar_entry_iter_end() afterwards.
 *
 * It is possible to begin iteration from an arbitrary entry within
 * the list by passing @prev. @prev is updated on return to point to
 * the last entry passed to @func. To begin iterating from the
 * beginning of the list @prev must be %NULL.
 *
 * The restrictions for @func are the same as documented for
 * efivar_entry_iter().
 */
int __efivar_entry_iter(int (*func)(struct efivar_entry *, void *),
                        struct list_head *head, void *data,
                        struct efivar_entry **prev)
{
        struct efivar_entry *entry, *n;
        int err = 0;

        if (!prev || !*prev) {
                list_for_each_entry_safe(entry, n, head, list) {
                        err = func(entry, data);
                        if (err)
                                break;
                }

                if (prev)
                        *prev = entry;

                return err;
        }


        list_for_each_entry_safe_continue((*prev), n, head, list) {
                err = func(*prev, data);
                if (err)
                        break;
        }

        return err;
}
EXPORT_SYMBOL_GPL(__efivar_entry_iter);

/**
 * efivar_entry_iter - iterate over variable list
 * @func: callback function
 * @head: head of variable list
 * @data: function-specific data to pass to callback
 *
 * Iterate over the list of EFI variables and call @func with every
 * entry on the list. It is safe for @func to remove entries in the
 * list via efivar_entry_delete() while iterating.
 *
 * Some notes for the callback function:
 *  - a non-zero return value indicates an error and terminates the loop
 *  - @func is called from atomic context
 */
int efivar_entry_iter(int (*func)(struct efivar_entry *, void *),
                      struct list_head *head, void *data)
{
        int err = 0;

        efivar_entry_iter_begin();
        err = __efivar_entry_iter(func, head, data, NULL);
        efivar_entry_iter_end();

        return err;
}
EXPORT_SYMBOL_GPL(efivar_entry_iter);

/**
 * efivars_kobject - get the kobject for the registered efivars
 *
 * If efivars_register() has not been called we return NULL,
 * otherwise return the kobject used at registration time.
 */
struct kobject *efivars_kobject(void)
{
        if (!__efivars)
                return NULL;

        return __efivars->kobject;
}
EXPORT_SYMBOL_GPL(efivars_kobject);

/**
 * efivar_run_worker - schedule the efivar worker thread
 */
void efivar_run_worker(void)
{
        if (efivar_wq_enabled)
                schedule_work(&efivar_work);
}
EXPORT_SYMBOL_GPL(efivar_run_worker);

/**
 * efivars_register - register an efivars
 * @efivars: efivars to register
 * @ops: efivars operations
 * @kobject: @efivars-specific kobject
 *
 * Only a single efivars can be registered at any time.
 */
int efivars_register(struct efivars *efivars,
                     const struct efivar_operations *ops,
                     struct kobject *kobject)
{
        spin_lock_init(&efivars->lock);
        efivars->ops = ops;
        efivars->kobject = kobject;

        __efivars = efivars;

        return 0;
}
EXPORT_SYMBOL_GPL(efivars_register);

/**
 * efivars_unregister - unregister an efivars
 * @efivars: efivars to unregister
 *
 * The caller must have already removed every entry from the list,
 * failure to do so is an error.
 */
int efivars_unregister(struct efivars *efivars)
{
        int rv;

        if (!__efivars) {
                printk(KERN_ERR "efivars not registered\n");
                rv = -EINVAL;
                goto out;
        }

        if (__efivars != efivars) {
                rv = -EINVAL;
                goto out;
        }

        __efivars = NULL;

        rv = 0;
out:
        return rv;
}
EXPORT_SYMBOL_GPL(efivars_unregister);