1 // SPDX-License-Identifier: BSD-2-Clause
3 * Copyright (C) 2017 The Android Open Source Project
6 #include <android_ab.h>
7 #include <android_bootloader_message.h>
12 #include <linux/err.h>
13 #include <u-boot/crc.h>
14 #include <u-boot/crc.h>
17 * Compute the CRC-32 of the bootloader control struct.
19 * Only the bytes up to the crc32_le field are considered for the CRC-32
22 * @param[in] abc bootloader control block
26 static uint32_t ab_control_compute_crc(struct bootloader_control *abc)
28 return crc32(0, (void *)abc, offsetof(typeof(*abc), crc32_le));
32 * Initialize bootloader_control to the default value.
34 * It allows us to boot all slots in order from the first one. This value
35 * should be used when the bootloader message is corrupted, but not when
36 * a valid message indicates that all slots are unbootable.
38 * @param[in] abc bootloader control block
40 * @return 0 on success and a negative on error
42 static int ab_control_default(struct bootloader_control *abc)
45 const struct slot_metadata metadata = {
49 .verity_corrupted = 0,
56 memcpy(abc->slot_suffix, "a\0\0\0", 4);
57 abc->magic = BOOT_CTRL_MAGIC;
58 abc->version = BOOT_CTRL_VERSION;
59 abc->nb_slot = NUM_SLOTS;
60 memset(abc->reserved0, 0, sizeof(abc->reserved0));
61 for (i = 0; i < abc->nb_slot; ++i)
62 abc->slot_info[i] = metadata;
64 memset(abc->reserved1, 0, sizeof(abc->reserved1));
65 abc->crc32_le = ab_control_compute_crc(abc);
71 * Load the boot_control struct from disk into newly allocated memory.
73 * This function allocates and returns an integer number of disk blocks,
74 * based on the block size of the passed device to help performing a
75 * read-modify-write operation on the boot_control struct.
76 * The boot_control struct offset (2 KiB) must be a multiple of the device
77 * block size, for simplicity.
79 * @param[in] dev_desc Device where to read the boot_control struct from
80 * @param[in] part_info Partition in 'dev_desc' where to read from, normally
81 * the "misc" partition should be used
82 * @param[out] pointer to pointer to bootloader_control data
83 * @return 0 on success and a negative on error
85 static int ab_control_create_from_disk(struct blk_desc *dev_desc,
86 const struct disk_partition *part_info,
87 struct bootloader_control **abc)
89 ulong abc_offset, abc_blocks, ret;
91 abc_offset = offsetof(struct bootloader_message_ab, slot_suffix);
92 if (abc_offset % part_info->blksz) {
93 log_err("ANDROID: Boot control block not block aligned.\n");
96 abc_offset /= part_info->blksz;
98 abc_blocks = DIV_ROUND_UP(sizeof(struct bootloader_control),
100 if (abc_offset + abc_blocks > part_info->size) {
101 log_err("ANDROID: boot control partition too small. Need at");
102 log_err(" least %lu blocks but have %lu blocks.\n",
103 abc_offset + abc_blocks, part_info->size);
106 *abc = malloc_cache_aligned(abc_blocks * part_info->blksz);
110 ret = blk_dread(dev_desc, part_info->start + abc_offset, abc_blocks,
112 if (IS_ERR_VALUE(ret)) {
113 log_err("ANDROID: Could not read from boot ctrl partition\n");
118 log_debug("ANDROID: Loaded ABC, %lu blocks\n", abc_blocks);
124 * Store the loaded boot_control block.
126 * Store back to the same location it was read from with
127 * ab_control_create_from_misc().
129 * @param[in] dev_desc Device where we should write the boot_control struct
130 * @param[in] part_info Partition on the 'dev_desc' where to write
131 * @param[in] abc Pointer to the boot control struct and the extra bytes after
132 * it up to the nearest block boundary
133 * @return 0 on success and a negative on error
135 static int ab_control_store(struct blk_desc *dev_desc,
136 const struct disk_partition *part_info,
137 struct bootloader_control *abc)
139 ulong abc_offset, abc_blocks, ret;
141 abc_offset = offsetof(struct bootloader_message_ab, slot_suffix) /
143 abc_blocks = DIV_ROUND_UP(sizeof(struct bootloader_control),
145 ret = blk_dwrite(dev_desc, part_info->start + abc_offset, abc_blocks,
147 if (IS_ERR_VALUE(ret)) {
148 log_err("ANDROID: Could not write back the misc partition\n");
158 * The function determines slot which is should we boot from among the two.
160 * @param[in] a The first bootable slot metadata
161 * @param[in] b The second bootable slot metadata
162 * @return Negative if the slot "a" is better, positive of the slot "b" is
163 * better or 0 if they are equally good.
165 static int ab_compare_slots(const struct slot_metadata *a,
166 const struct slot_metadata *b)
168 /* Higher priority is better */
169 if (a->priority != b->priority)
170 return b->priority - a->priority;
172 /* Higher successful_boot value is better, in case of same priority */
173 if (a->successful_boot != b->successful_boot)
174 return b->successful_boot - a->successful_boot;
176 /* Higher tries_remaining is better to ensure round-robin */
177 if (a->tries_remaining != b->tries_remaining)
178 return b->tries_remaining - a->tries_remaining;
183 int ab_select_slot(struct blk_desc *dev_desc, struct disk_partition *part_info)
185 struct bootloader_control *abc = NULL;
188 bool store_needed = false;
191 ret = ab_control_create_from_disk(dev_desc, part_info, &abc);
194 * This condition represents an actual problem with the code or
195 * the board setup, like an invalid partition information.
196 * Signal a repair mode and do not try to boot from either slot.
201 crc32_le = ab_control_compute_crc(abc);
202 if (abc->crc32_le != crc32_le) {
203 log_err("ANDROID: Invalid CRC-32 (expected %.8x, found %.8x),",
204 crc32_le, abc->crc32_le);
205 log_err("re-initializing A/B metadata.\n");
207 ret = ab_control_default(abc);
215 if (abc->magic != BOOT_CTRL_MAGIC) {
216 log_err("ANDROID: Unknown A/B metadata: %.8x\n", abc->magic);
221 if (abc->version > BOOT_CTRL_VERSION) {
222 log_err("ANDROID: Unsupported A/B metadata version: %.8x\n",
229 * At this point a valid boot control metadata is stored in abc,
230 * followed by other reserved data in the same block. We select a with
231 * the higher priority slot that
232 * - is not marked as corrupted and
233 * - either has tries_remaining > 0 or successful_boot is true.
234 * If the selected slot has a false successful_boot, we also decrement
235 * the tries_remaining until it eventually becomes unbootable because
236 * tries_remaining reaches 0. This mechanism produces a bootloader
237 * induced rollback, typically right after a failed update.
240 /* Safety check: limit the number of slots. */
241 if (abc->nb_slot > ARRAY_SIZE(abc->slot_info)) {
242 abc->nb_slot = ARRAY_SIZE(abc->slot_info);
247 for (i = 0; i < abc->nb_slot; ++i) {
248 if (abc->slot_info[i].verity_corrupted ||
249 !abc->slot_info[i].tries_remaining) {
250 log_debug("ANDROID: unbootable slot %d tries: %d, ",
251 i, abc->slot_info[i].tries_remaining);
252 log_debug("corrupt: %d\n",
253 abc->slot_info[i].verity_corrupted);
256 log_debug("ANDROID: bootable slot %d pri: %d, tries: %d, ",
257 i, abc->slot_info[i].priority,
258 abc->slot_info[i].tries_remaining);
259 log_debug("corrupt: %d, successful: %d\n",
260 abc->slot_info[i].verity_corrupted,
261 abc->slot_info[i].successful_boot);
264 ab_compare_slots(&abc->slot_info[i],
265 &abc->slot_info[slot]) < 0) {
270 if (slot >= 0 && !abc->slot_info[slot].successful_boot) {
271 log_err("ANDROID: Attempting slot %c, tries remaining %d\n",
272 BOOT_SLOT_NAME(slot),
273 abc->slot_info[slot].tries_remaining);
274 abc->slot_info[slot].tries_remaining--;
280 * Legacy user-space requires this field to be set in the BCB.
281 * Newer releases load this slot suffix from the command line
282 * or the device tree.
284 memset(slot_suffix, 0, sizeof(slot_suffix));
285 slot_suffix[0] = BOOT_SLOT_NAME(slot);
286 if (memcmp(abc->slot_suffix, slot_suffix,
287 sizeof(slot_suffix))) {
288 memcpy(abc->slot_suffix, slot_suffix,
289 sizeof(slot_suffix));
295 abc->crc32_le = ab_control_compute_crc(abc);
296 ab_control_store(dev_desc, part_info, abc);