1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * mokvar-table.c
4  *
5  * Copyright (c) 2020 Red Hat
6  * Author: Lenny Szubowicz <lszubowi@redhat.com>
7  *
8  * This module contains the kernel support for the Linux EFI Machine
9  * Owner Key (MOK) variable configuration table, which is identified by
10  * the LINUX_EFI_MOK_VARIABLE_TABLE_GUID.
11  *
12  * This EFI configuration table provides a more robust alternative to
13  * EFI volatile variables by which an EFI boot loader can pass the
14  * contents of the Machine Owner Key (MOK) certificate stores to the
15  * kernel during boot. If both the EFI MOK config table and corresponding
16  * EFI MOK variables are present, the table should be considered as
17  * more authoritative.
18  *
19  * This module includes code that validates and maps the EFI MOK table,
20  * if it's presence was detected very early in boot.
21  *
22  * Kernel interface routines are provided to walk through all the
23  * entries in the MOK config table or to search for a specific named
24  * entry.
25  *
26  * The contents of the individual named MOK config table entries are
27  * made available to user space via read-only sysfs binary files under:
28  *
29  * /sys/firmware/efi/mok-variables/
30  *
31  */
32 #define pr_fmt(fmt) "mokvar: " fmt
33 
34 #include <linux/capability.h>
35 #include <linux/efi.h>
36 #include <linux/init.h>
37 #include <linux/io.h>
38 #include <linux/kernel.h>
39 #include <linux/kobject.h>
40 #include <linux/list.h>
41 #include <linux/slab.h>
42 
43 #include <asm/early_ioremap.h>
44 
45 /*
46  * The LINUX_EFI_MOK_VARIABLE_TABLE_GUID config table is a packed
47  * sequence of struct efi_mokvar_table_entry, one for each named
48  * MOK variable. The sequence is terminated by an entry with a
49  * completely NULL name and 0 data size.
50  *
51  * efi_mokvar_table_size is set to the computed size of the
52  * MOK config table by efi_mokvar_table_init(). This will be
53  * non-zero if and only if the table if present and has been
54  * validated by efi_mokvar_table_init().
55  */
56 static size_t efi_mokvar_table_size;
57 
58 /*
59  * efi_mokvar_table_va is the kernel virtual address at which the
60  * EFI MOK config table has been mapped by efi_mokvar_sysfs_init().
61  */
62 static struct efi_mokvar_table_entry *efi_mokvar_table_va;
63 
64 /*
65  * Each /sys/firmware/efi/mok-variables/ sysfs file is represented by
66  * an instance of struct efi_mokvar_sysfs_attr on efi_mokvar_sysfs_list.
67  * bin_attr.private points to the associated EFI MOK config table entry.
68  *
69  * This list is created during boot and then remains unchanged.
70  * So no synchronization is currently required to walk the list.
71  */
72 struct efi_mokvar_sysfs_attr {
73 	struct bin_attribute bin_attr;
74 	struct list_head node;
75 };
76 
77 static LIST_HEAD(efi_mokvar_sysfs_list);
78 static struct kobject *mokvar_kobj;
79 
80 /*
81  * efi_mokvar_table_init() - Early boot validation of EFI MOK config table
82  *
83  * If present, validate and compute the size of the EFI MOK variable
84  * configuration table. This table may be provided by an EFI boot loader
85  * as an alternative to ordinary EFI variables, due to platform-dependent
86  * limitations. The memory occupied by this table is marked as reserved.
87  *
88  * This routine must be called before efi_free_boot_services() in order
89  * to guarantee that it can mark the table as reserved.
90  *
91  * Implicit inputs:
92  * efi.mokvar_table:	Physical address of EFI MOK variable config table
93  *			or special value that indicates no such table.
94  *
95  * Implicit outputs:
96  * efi_mokvar_table_size: Computed size of EFI MOK variable config table.
97  *			The table is considered present and valid if this
98  *			is non-zero.
99  */
100 void __init efi_mokvar_table_init(void)
101 {
102 	efi_memory_desc_t md;
103 	void *va = NULL;
104 	unsigned long cur_offset = 0;
105 	unsigned long offset_limit;
106 	unsigned long map_size = 0;
107 	unsigned long map_size_needed = 0;
108 	unsigned long size;
109 	struct efi_mokvar_table_entry *mokvar_entry;
110 	int err;
111 
112 	if (!efi_enabled(EFI_MEMMAP))
113 		return;
114 
115 	if (efi.mokvar_table == EFI_INVALID_TABLE_ADDR)
116 		return;
117 	/*
118 	 * The EFI MOK config table must fit within a single EFI memory
119 	 * descriptor range.
120 	 */
121 	err = efi_mem_desc_lookup(efi.mokvar_table, &md);
122 	if (err) {
123 		pr_warn("EFI MOKvar config table is not within the EFI memory map\n");
124 		return;
125 	}
126 
127 	offset_limit = efi_mem_desc_end(&md) - efi.mokvar_table;
128 
129 	/*
130 	 * Validate the MOK config table. Since there is no table header
131 	 * from which we could get the total size of the MOK config table,
132 	 * we compute the total size as we validate each variably sized
133 	 * entry, remapping as necessary.
134 	 */
135 	err = -EINVAL;
136 	while (cur_offset + sizeof(*mokvar_entry) <= offset_limit) {
137 		mokvar_entry = va + cur_offset;
138 		map_size_needed = cur_offset + sizeof(*mokvar_entry);
139 		if (map_size_needed > map_size) {
140 			if (va)
141 				early_memunmap(va, map_size);
142 			/*
143 			 * Map a little more than the fixed size entry
144 			 * header, anticipating some data. It's safe to
145 			 * do so as long as we stay within current memory
146 			 * descriptor.
147 			 */
148 			map_size = min(map_size_needed + 2*EFI_PAGE_SIZE,
149 				       offset_limit);
150 			va = early_memremap(efi.mokvar_table, map_size);
151 			if (!va) {
152 				pr_err("Failed to map EFI MOKvar config table pa=0x%lx, size=%lu.\n",
153 				       efi.mokvar_table, map_size);
154 				return;
155 			}
156 			mokvar_entry = va + cur_offset;
157 		}
158 
159 		/* Check for last sentinel entry */
160 		if (mokvar_entry->name[0] == '\0') {
161 			if (mokvar_entry->data_size != 0)
162 				break;
163 			err = 0;
164 			break;
165 		}
166 
167 		/* Sanity check that the name is null terminated */
168 		size = strnlen(mokvar_entry->name,
169 			       sizeof(mokvar_entry->name));
170 		if (size >= sizeof(mokvar_entry->name))
171 			break;
172 
173 		/* Advance to the next entry */
174 		cur_offset = map_size_needed + mokvar_entry->data_size;
175 	}
176 
177 	if (va)
178 		early_memunmap(va, map_size);
179 	if (err) {
180 		pr_err("EFI MOKvar config table is not valid\n");
181 		return;
182 	}
183 
184 	if (md.type == EFI_BOOT_SERVICES_DATA)
185 		efi_mem_reserve(efi.mokvar_table, map_size_needed);
186 
187 	efi_mokvar_table_size = map_size_needed;
188 }
189 
190 /*
191  * efi_mokvar_entry_next() - Get next entry in the EFI MOK config table
192  *
193  * mokvar_entry:	Pointer to current EFI MOK config table entry
194  *			or null. Null indicates get first entry.
195  *			Passed by reference. This is updated to the
196  *			same value as the return value.
197  *
198  * Returns:		Pointer to next EFI MOK config table entry
199  *			or null, if there are no more entries.
200  *			Same value is returned in the mokvar_entry
201  *			parameter.
202  *
203  * This routine depends on the EFI MOK config table being entirely
204  * mapped with it's starting virtual address in efi_mokvar_table_va.
205  */
206 struct efi_mokvar_table_entry *efi_mokvar_entry_next(
207 			struct efi_mokvar_table_entry **mokvar_entry)
208 {
209 	struct efi_mokvar_table_entry *mokvar_cur;
210 	struct efi_mokvar_table_entry *mokvar_next;
211 	size_t size_cur;
212 
213 	mokvar_cur = *mokvar_entry;
214 	*mokvar_entry = NULL;
215 
216 	if (efi_mokvar_table_va == NULL)
217 		return NULL;
218 
219 	if (mokvar_cur == NULL) {
220 		mokvar_next = efi_mokvar_table_va;
221 	} else {
222 		if (mokvar_cur->name[0] == '\0')
223 			return NULL;
224 		size_cur = sizeof(*mokvar_cur) + mokvar_cur->data_size;
225 		mokvar_next = (void *)mokvar_cur + size_cur;
226 	}
227 
228 	if (mokvar_next->name[0] == '\0')
229 		return NULL;
230 
231 	*mokvar_entry = mokvar_next;
232 	return mokvar_next;
233 }
234 
235 /*
236  * efi_mokvar_entry_find() - Find EFI MOK config entry by name
237  *
238  * name:	Name of the entry to look for.
239  *
240  * Returns:	Pointer to EFI MOK config table entry if found;
241  *		null otherwise.
242  *
243  * This routine depends on the EFI MOK config table being entirely
244  * mapped with it's starting virtual address in efi_mokvar_table_va.
245  */
246 struct efi_mokvar_table_entry *efi_mokvar_entry_find(const char *name)
247 {
248 	struct efi_mokvar_table_entry *mokvar_entry = NULL;
249 
250 	while (efi_mokvar_entry_next(&mokvar_entry)) {
251 		if (!strncmp(name, mokvar_entry->name,
252 			     sizeof(mokvar_entry->name)))
253 			return mokvar_entry;
254 	}
255 	return NULL;
256 }
257 
258 /*
259  * efi_mokvar_sysfs_read() - sysfs binary file read routine
260  *
261  * Returns:	Count of bytes read.
262  *
263  * Copy EFI MOK config table entry data for this mokvar sysfs binary file
264  * to the supplied buffer, starting at the specified offset into mokvar table
265  * entry data, for the specified count bytes. The copy is limited by the
266  * amount of data in this mokvar config table entry.
267  */
268 static ssize_t efi_mokvar_sysfs_read(struct file *file, struct kobject *kobj,
269 				 struct bin_attribute *bin_attr, char *buf,
270 				 loff_t off, size_t count)
271 {
272 	struct efi_mokvar_table_entry *mokvar_entry = bin_attr->private;
273 
274 	if (!capable(CAP_SYS_ADMIN))
275 		return 0;
276 
277 	if (off >= mokvar_entry->data_size)
278 		return 0;
279 	if (count >  mokvar_entry->data_size - off)
280 		count = mokvar_entry->data_size - off;
281 
282 	memcpy(buf, mokvar_entry->data + off, count);
283 	return count;
284 }
285 
286 /*
287  * efi_mokvar_sysfs_init() - Map EFI MOK config table and create sysfs
288  *
289  * Map the EFI MOK variable config table for run-time use by the kernel
290  * and create the sysfs entries in /sys/firmware/efi/mok-variables/
291  *
292  * This routine just returns if a valid EFI MOK variable config table
293  * was not found earlier during boot.
294  *
295  * This routine must be called during a "middle" initcall phase, i.e.
296  * after efi_mokvar_table_init() but before UEFI certs are loaded
297  * during late init.
298  *
299  * Implicit inputs:
300  * efi.mokvar_table:	Physical address of EFI MOK variable config table
301  *			or special value that indicates no such table.
302  *
303  * efi_mokvar_table_size: Computed size of EFI MOK variable config table.
304  *			The table is considered present and valid if this
305  *			is non-zero.
306  *
307  * Implicit outputs:
308  * efi_mokvar_table_va:	Start virtual address of the EFI MOK config table.
309  */
310 static int __init efi_mokvar_sysfs_init(void)
311 {
312 	void *config_va;
313 	struct efi_mokvar_table_entry *mokvar_entry = NULL;
314 	struct efi_mokvar_sysfs_attr *mokvar_sysfs = NULL;
315 	int err = 0;
316 
317 	if (efi_mokvar_table_size == 0)
318 		return -ENOENT;
319 
320 	config_va = memremap(efi.mokvar_table, efi_mokvar_table_size,
321 			     MEMREMAP_WB);
322 	if (!config_va) {
323 		pr_err("Failed to map EFI MOKvar config table\n");
324 		return -ENOMEM;
325 	}
326 	efi_mokvar_table_va = config_va;
327 
328 	mokvar_kobj = kobject_create_and_add("mok-variables", efi_kobj);
329 	if (!mokvar_kobj) {
330 		pr_err("Failed to create EFI mok-variables sysfs entry\n");
331 		return -ENOMEM;
332 	}
333 
334 	while (efi_mokvar_entry_next(&mokvar_entry)) {
335 		mokvar_sysfs = kzalloc(sizeof(*mokvar_sysfs), GFP_KERNEL);
336 		if (!mokvar_sysfs) {
337 			err = -ENOMEM;
338 			break;
339 		}
340 
341 		sysfs_bin_attr_init(&mokvar_sysfs->bin_attr);
342 		mokvar_sysfs->bin_attr.private = mokvar_entry;
343 		mokvar_sysfs->bin_attr.attr.name = mokvar_entry->name;
344 		mokvar_sysfs->bin_attr.attr.mode = 0400;
345 		mokvar_sysfs->bin_attr.size = mokvar_entry->data_size;
346 		mokvar_sysfs->bin_attr.read = efi_mokvar_sysfs_read;
347 
348 		err = sysfs_create_bin_file(mokvar_kobj,
349 					   &mokvar_sysfs->bin_attr);
350 		if (err)
351 			break;
352 
353 		list_add_tail(&mokvar_sysfs->node, &efi_mokvar_sysfs_list);
354 	}
355 
356 	if (err) {
357 		pr_err("Failed to create some EFI mok-variables sysfs entries\n");
358 		kfree(mokvar_sysfs);
359 	}
360 	return err;
361 }
362 device_initcall(efi_mokvar_sysfs_init);
363