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// 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;
}
fs_initcall(efi_mokvar_sysfs_init);