// SPDX-License-Identifier: GPL-2.0
/*
 * mokvar-table.c
 *
 * Copyright (c) 2020 Red Hat
 * Author: Lenny Szubowicz <lszubowi@redhat.com>
 *
 * This module contains the kernel support for the Linux EFI Machine
 * Owner Key (MOK) variable configuration table, which is identified by
 * the LINUX_EFI_MOK_VARIABLE_TABLE_GUID.
 *
 * This EFI configuration table provides a more robust alternative to
 * EFI volatile variables by which an EFI boot loader can pass the
 * contents of the Machine Owner Key (MOK) certificate stores to the
 * kernel during boot. If both the EFI MOK config table and corresponding
 * EFI MOK variables are present, the table should be considered as
 * more authoritative.
 *
 * This module includes code that validates and maps the EFI MOK table,
 * if it's presence was detected very early in boot.
 *
 * Kernel interface routines are provided to walk through all the
 * entries in the MOK config table or to search for a specific named
 * entry.
 *
 * The contents of the individual named MOK config table entries are
 * made available to user space via read-only sysfs binary files under:
 *
 * /sys/firmware/efi/mok-variables/
 *
 */
#define pr_fmt(fmt) "mokvar: " fmt

#include <linux/capability.h>
#include <linux/efi.h>
#include <linux/init.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <linux/kobject.h>
#include <linux/list.h>
#include <linux/slab.h>

#include <asm/early_ioremap.h>

/*
 * The LINUX_EFI_MOK_VARIABLE_TABLE_GUID config table is a packed
 * sequence of struct efi_mokvar_table_entry, one for each named
 * MOK variable. The sequence is terminated by an entry with a
 * completely NULL name and 0 data size.
 *
 * efi_mokvar_table_size is set to the computed size of the
 * MOK config table by efi_mokvar_table_init(). This will be
 * non-zero if and only if the table if present and has been
 * validated by efi_mokvar_table_init().
 */
static size_t efi_mokvar_table_size;

/*
 * efi_mokvar_table_va is the kernel virtual address at which the
 * EFI MOK config table has been mapped by efi_mokvar_sysfs_init().
 */
static struct efi_mokvar_table_entry *efi_mokvar_table_va;

/*
 * Each /sys/firmware/efi/mok-variables/ sysfs file is represented by
 * an instance of struct efi_mokvar_sysfs_attr on efi_mokvar_sysfs_list.
 * bin_attr.private points to the associated EFI MOK config table entry.
 *
 * This list is created during boot and then remains unchanged.
 * So no synchronization is currently required to walk the list.
 */
struct efi_mokvar_sysfs_attr {
        struct bin_attribute bin_attr;
        struct list_head node;
};

static LIST_HEAD(efi_mokvar_sysfs_list);
static struct kobject *mokvar_kobj;

/*
 * efi_mokvar_table_init() - Early boot validation of EFI MOK config table
 *
 * If present, validate and compute the size of the EFI MOK variable
 * configuration table. This table may be provided by an EFI boot loader
 * as an alternative to ordinary EFI variables, due to platform-dependent
 * limitations. The memory occupied by this table is marked as reserved.
 *
 * This routine must be called before efi_free_boot_services() in order
 * to guarantee that it can mark the table as reserved.
 *
 * Implicit inputs:
 * efi.mokvar_table:    Physical address of EFI MOK variable config table
 *                      or special value that indicates no such table.
 *
 * Implicit outputs:
 * efi_mokvar_table_size: Computed size of EFI MOK variable config table.
 *                      The table is considered present and valid if this
 *                      is non-zero.
 */
void __init efi_mokvar_table_init(void)
{
        efi_memory_desc_t md;
        void *va = NULL;
        unsigned long cur_offset = 0;
        unsigned long offset_limit;
        unsigned long map_size = 0;
        unsigned long map_size_needed = 0;
        unsigned long size;
        struct efi_mokvar_table_entry *mokvar_entry;
        int err;

        if (!efi_enabled(EFI_MEMMAP))
                return;

        if (efi.mokvar_table == EFI_INVALID_TABLE_ADDR)
                return;
        /*
         * The EFI MOK config table must fit within a single EFI memory
         * descriptor range.
         */
        err = efi_mem_desc_lookup(efi.mokvar_table, &md);
        if (err) {
                pr_warn("EFI MOKvar config table is not within the EFI memory map\n");
                return;
        }

        offset_limit = efi_mem_desc_end(&md) - efi.mokvar_table;

        /*
         * Validate the MOK config table. Since there is no table header
         * from which we could get the total size of the MOK config table,
         * we compute the total size as we validate each variably sized
         * entry, remapping as necessary.
         */
        err = -EINVAL;
        while (cur_offset + sizeof(*mokvar_entry) <= offset_limit) {
                mokvar_entry = va + cur_offset;
                map_size_needed = cur_offset + sizeof(*mokvar_entry);
                if (map_size_needed > map_size) {
                        if (va)
                                early_memunmap(va, map_size);
                        /*
                         * Map a little more than the fixed size entry
                         * header, anticipating some data. It's safe to
                         * do so as long as we stay within current memory
                         * descriptor.
                         */
                        map_size = min(map_size_needed + 2*EFI_PAGE_SIZE,
                                       offset_limit);
                        va = early_memremap(efi.mokvar_table, map_size);
                        if (!va) {
                                pr_err("Failed to map EFI MOKvar config table pa=0x%lx, size=%lu.\n",
                                       efi.mokvar_table, map_size);
                                return;
                        }
                        mokvar_entry = va + cur_offset;
                }

                /* Check for last sentinel entry */
                if (mokvar_entry->name[0] == '\0') {
                        if (mokvar_entry->data_size != 0)
                                break;
                        err = 0;
                        break;
                }

                /* Sanity check that the name is null terminated */
                size = strnlen(mokvar_entry->name,
                               sizeof(mokvar_entry->name));
                if (size >= sizeof(mokvar_entry->name))
                        break;

                /* Advance to the next entry */
                cur_offset = map_size_needed + mokvar_entry->data_size;
        }

        if (va)
                early_memunmap(va, map_size);
        if (err) {
                pr_err("EFI MOKvar config table is not valid\n");
                return;
        }

        if (md.type == EFI_BOOT_SERVICES_DATA)
                efi_mem_reserve(efi.mokvar_table, map_size_needed);

        efi_mokvar_table_size = map_size_needed;
}

/*
 * efi_mokvar_entry_next() - Get next entry in the EFI MOK config table
 *
 * mokvar_entry:        Pointer to current EFI MOK config table entry
 *                      or null. Null indicates get first entry.
 *                      Passed by reference. This is updated to the
 *                      same value as the return value.
 *
 * Returns:             Pointer to next EFI MOK config table entry
 *                      or null, if there are no more entries.
 *                      Same value is returned in the mokvar_entry
 *                      parameter.
 *
 * This routine depends on the EFI MOK config table being entirely
 * mapped with it's starting virtual address in efi_mokvar_table_va.
 */
struct efi_mokvar_table_entry *efi_mokvar_entry_next(
                        struct efi_mokvar_table_entry **mokvar_entry)
{
        struct efi_mokvar_table_entry *mokvar_cur;
        struct efi_mokvar_table_entry *mokvar_next;
        size_t size_cur;

        mokvar_cur = *mokvar_entry;
        *mokvar_entry = NULL;

        if (efi_mokvar_table_va == NULL)
                return NULL;

        if (mokvar_cur == NULL) {
                mokvar_next = efi_mokvar_table_va;
        } else {
                if (mokvar_cur->name[0] == '\0')
                        return NULL;
                size_cur = sizeof(*mokvar_cur) + mokvar_cur->data_size;
                mokvar_next = (void *)mokvar_cur + size_cur;
        }

        if (mokvar_next->name[0] == '\0')
                return NULL;

        *mokvar_entry = mokvar_next;
        return mokvar_next;
}

/*
 * efi_mokvar_entry_find() - Find EFI MOK config entry by name
 *
 * name:        Name of the entry to look for.
 *
 * Returns:     Pointer to EFI MOK config table entry if found;
 *              null otherwise.
 *
 * This routine depends on the EFI MOK config table being entirely
 * mapped with it's starting virtual address in efi_mokvar_table_va.
 */
struct efi_mokvar_table_entry *efi_mokvar_entry_find(const char *name)
{
        struct efi_mokvar_table_entry *mokvar_entry = NULL;

        while (efi_mokvar_entry_next(&mokvar_entry)) {
                if (!strncmp(name, mokvar_entry->name,
                             sizeof(mokvar_entry->name)))
                        return mokvar_entry;
        }
        return NULL;
}

/*
 * efi_mokvar_sysfs_read() - sysfs binary file read routine
 *
 * Returns:     Count of bytes read.
 *
 * Copy EFI MOK config table entry data for this mokvar sysfs binary file
 * to the supplied buffer, starting at the specified offset into mokvar table
 * entry data, for the specified count bytes. The copy is limited by the
 * amount of data in this mokvar config table entry.
 */
static ssize_t efi_mokvar_sysfs_read(struct file *file, struct kobject *kobj,
                                 struct bin_attribute *bin_attr, char *buf,
                                 loff_t off, size_t count)
{
        struct efi_mokvar_table_entry *mokvar_entry = bin_attr->private;

        if (!capable(CAP_SYS_ADMIN))
                return 0;

        if (off >= mokvar_entry->data_size)
                return 0;
        if (count >  mokvar_entry->data_size - off)
                count = mokvar_entry->data_size - off;

        memcpy(buf, mokvar_entry->data + off, count);
        return count;
}

/*
 * efi_mokvar_sysfs_init() - Map EFI MOK config table and create sysfs
 *
 * Map the EFI MOK variable config table for run-time use by the kernel
 * and create the sysfs entries in /sys/firmware/efi/mok-variables/
 *
 * This routine just returns if a valid EFI MOK variable config table
 * was not found earlier during boot.
 *
 * This routine must be called during a "middle" initcall phase, i.e.
 * after efi_mokvar_table_init() but before UEFI certs are loaded
 * during late init.
 *
 * Implicit inputs:
 * efi.mokvar_table:    Physical address of EFI MOK variable config table
 *                      or special value that indicates no such table.
 *
 * efi_mokvar_table_size: Computed size of EFI MOK variable config table.
 *                      The table is considered present and valid if this
 *                      is non-zero.
 *
 * Implicit outputs:
 * efi_mokvar_table_va: Start virtual address of the EFI MOK config table.
 */
static int __init efi_mokvar_sysfs_init(void)
{
        void *config_va;
        struct efi_mokvar_table_entry *mokvar_entry = NULL;
        struct efi_mokvar_sysfs_attr *mokvar_sysfs = NULL;
        int err = 0;

        if (efi_mokvar_table_size == 0)
                return -ENOENT;

        config_va = memremap(efi.mokvar_table, efi_mokvar_table_size,
                             MEMREMAP_WB);
        if (!config_va) {
                pr_err("Failed to map EFI MOKvar config table\n");
                return -ENOMEM;
        }
        efi_mokvar_table_va = config_va;

        mokvar_kobj = kobject_create_and_add("mok-variables", efi_kobj);
        if (!mokvar_kobj) {
                pr_err("Failed to create EFI mok-variables sysfs entry\n");
                return -ENOMEM;
        }

        while (efi_mokvar_entry_next(&mokvar_entry)) {
                mokvar_sysfs = kzalloc(sizeof(*mokvar_sysfs), GFP_KERNEL);
                if (!mokvar_sysfs) {
                        err = -ENOMEM;
                        break;
                }

                sysfs_bin_attr_init(&mokvar_sysfs->bin_attr);
                mokvar_sysfs->bin_attr.private = mokvar_entry;
                mokvar_sysfs->bin_attr.attr.name = mokvar_entry->name;
                mokvar_sysfs->bin_attr.attr.mode = 0400;
                mokvar_sysfs->bin_attr.size = mokvar_entry->data_size;
                mokvar_sysfs->bin_attr.read = efi_mokvar_sysfs_read;

                err = sysfs_create_bin_file(mokvar_kobj,
                                           &mokvar_sysfs->bin_attr);
                if (err)
                        break;

                list_add_tail(&mokvar_sysfs->node, &efi_mokvar_sysfs_list);
        }

        if (err) {
                pr_err("Failed to create some EFI mok-variables sysfs entries\n");
                kfree(mokvar_sysfs);
        }
        return err;
}
device_initcall(efi_mokvar_sysfs_init);