common/android_ab.c

   1 // SPDX-License-Identifier: BSD-2-Clause
   2 /*
   3  * Copyright (C) 2017 The Android Open Source Project
   4  */
   5 #include <common.h>
   6 #include <android_ab.h>
   7 #include <android_bootloader_message.h>
   8 #include <linux/err.h>
   9 #include <memalign.h>
  10 #include <u-boot/crc.h>
  11
  12 /**
  13  * Compute the CRC-32 of the bootloader control struct.
  14  *
  15  * Only the bytes up to the crc32_le field are considered for the CRC-32
  16  * calculation.
  17  *
  18  * @param[in] abc bootloader control block
  19  *
  20  * @return crc32 sum
  21  */
  22 static uint32_t ab_control_compute_crc(struct bootloader_control *abc)
  23 {
  24         return crc32(0, (void *)abc, offsetof(typeof(*abc), crc32_le));
  25 }
  26
  27 /**
  28  * Initialize bootloader_control to the default value.
  29  *
  30  * It allows us to boot all slots in order from the first one. This value
  31  * should be used when the bootloader message is corrupted, but not when
  32  * a valid message indicates that all slots are unbootable.
  33  *
  34  * @param[in] abc bootloader control block
  35  *
  36  * @return 0 on success and a negative on error
  37  */
  38 static int ab_control_default(struct bootloader_control *abc)
  39 {
  40         int i;
  41         const struct slot_metadata metadata = {
  42                 .priority = 15,
  43                 .tries_remaining = 7,
  44                 .successful_boot = 0,
  45                 .verity_corrupted = 0,
  46                 .reserved = 0
  47         };
  48
  49         if (!abc)
  50                 return -EFAULT;
  51
  52         memcpy(abc->slot_suffix, "a\0\0\0", 4);
  53         abc->magic = BOOT_CTRL_MAGIC;
  54         abc->version = BOOT_CTRL_VERSION;
  55         abc->nb_slot = NUM_SLOTS;
  56         memset(abc->reserved0, 0, sizeof(abc->reserved0));
  57         for (i = 0; i < abc->nb_slot; ++i)
  58                 abc->slot_info[i] = metadata;
  59
  60         memset(abc->reserved1, 0, sizeof(abc->reserved1));
  61         abc->crc32_le = ab_control_compute_crc(abc);
  62
  63         return 0;
  64 }
  65
  66 /**
  67  * Load the boot_control struct from disk into newly allocated memory.
  68  *
  69  * This function allocates and returns an integer number of disk blocks,
  70  * based on the block size of the passed device to help performing a
  71  * read-modify-write operation on the boot_control struct.
  72  * The boot_control struct offset (2 KiB) must be a multiple of the device
  73  * block size, for simplicity.
  74  *
  75  * @param[in] dev_desc Device where to read the boot_control struct from
  76  * @param[in] part_info Partition in 'dev_desc' where to read from, normally
  77  *                      the "misc" partition should be used
  78  * @param[out] pointer to pointer to bootloader_control data
  79  * @return 0 on success and a negative on error
  80  */
  81 static int ab_control_create_from_disk(struct blk_desc *dev_desc,
  82                                        const disk_partition_t *part_info,
  83                                        struct bootloader_control **abc)
  84 {
  85         ulong abc_offset, abc_blocks, ret;
  86
  87         abc_offset = offsetof(struct bootloader_message_ab, slot_suffix);
  88         if (abc_offset % part_info->blksz) {
  89                 log_err("ANDROID: Boot control block not block aligned.\n");
  90                 return -EINVAL;
  91         }
  92         abc_offset /= part_info->blksz;
  93
  94         abc_blocks = DIV_ROUND_UP(sizeof(struct bootloader_control),
  95                                   part_info->blksz);
  96         if (abc_offset + abc_blocks > part_info->size) {
  97                 log_err("ANDROID: boot control partition too small. Need at");
  98                 log_err(" least %lu blocks but have %lu blocks.\n",
  99                         abc_offset + abc_blocks, part_info->size);
 100                 return -EINVAL;
 101         }
 102         *abc = malloc_cache_aligned(abc_blocks * part_info->blksz);
 103         if (!*abc)
 104                 return -ENOMEM;
 105
 106         ret = blk_dread(dev_desc, part_info->start + abc_offset, abc_blocks,
 107                         *abc);
 108         if (IS_ERR_VALUE(ret)) {
 109                 log_err("ANDROID: Could not read from boot ctrl partition\n");
 110                 free(*abc);
 111                 return -EIO;
 112         }
 113
 114         log_debug("ANDROID: Loaded ABC, %lu blocks\n", abc_blocks);
 115
 116         return 0;
 117 }
 118
 119 /**
 120  * Store the loaded boot_control block.
 121  *
 122  * Store back to the same location it was read from with
 123  * ab_control_create_from_misc().
 124  *
 125  * @param[in] dev_desc Device where we should write the boot_control struct
 126  * @param[in] part_info Partition on the 'dev_desc' where to write
 127  * @param[in] abc Pointer to the boot control struct and the extra bytes after
 128  *                it up to the nearest block boundary
 129  * @return 0 on success and a negative on error
 130  */
 131 static int ab_control_store(struct blk_desc *dev_desc,
 132                             const disk_partition_t *part_info,
 133                             struct bootloader_control *abc)
 134 {
 135         ulong abc_offset, abc_blocks, ret;
 136
 137         abc_offset = offsetof(struct bootloader_message_ab, slot_suffix) /
 138                      part_info->blksz;
 139         abc_blocks = DIV_ROUND_UP(sizeof(struct bootloader_control),
 140                                   part_info->blksz);
 141         ret = blk_dwrite(dev_desc, part_info->start + abc_offset, abc_blocks,
 142                          abc);
 143         if (IS_ERR_VALUE(ret)) {
 144                 log_err("ANDROID: Could not write back the misc partition\n");
 145                 return -EIO;
 146         }
 147
 148         return 0;
 149 }
 150
 151 /**
 152  * Compare two slots.
 153  *
 154  * The function determines slot which is should we boot from among the two.
 155  *
 156  * @param[in] a The first bootable slot metadata
 157  * @param[in] b The second bootable slot metadata
 158  * @return Negative if the slot "a" is better, positive of the slot "b" is
 159  *         better or 0 if they are equally good.
 160  */
 161 static int ab_compare_slots(const struct slot_metadata *a,
 162                             const struct slot_metadata *b)
 163 {
 164         /* Higher priority is better */
 165         if (a->priority != b->priority)
 166                 return b->priority - a->priority;
 167
 168         /* Higher successful_boot value is better, in case of same priority */
 169         if (a->successful_boot != b->successful_boot)
 170                 return b->successful_boot - a->successful_boot;
 171
 172         /* Higher tries_remaining is better to ensure round-robin */
 173         if (a->tries_remaining != b->tries_remaining)
 174                 return b->tries_remaining - a->tries_remaining;
 175
 176         return 0;
 177 }
 178
 179 int ab_select_slot(struct blk_desc *dev_desc, disk_partition_t *part_info)
 180 {
 181         struct bootloader_control *abc = NULL;
 182         u32 crc32_le;
 183         int slot, i, ret;
 184         bool store_needed = false;
 185         char slot_suffix[4];
 186
 187         ret = ab_control_create_from_disk(dev_desc, part_info, &abc);
 188         if (ret < 0) {
 189                 /*
 190                  * This condition represents an actual problem with the code or
 191                  * the board setup, like an invalid partition information.
 192                  * Signal a repair mode and do not try to boot from either slot.
 193                  */
 194                 return ret;
 195         }
 196
 197         crc32_le = ab_control_compute_crc(abc);
 198         if (abc->crc32_le != crc32_le) {
 199                 log_err("ANDROID: Invalid CRC-32 (expected %.8x, found %.8x),",
 200                         crc32_le, abc->crc32_le);
 201                 log_err("re-initializing A/B metadata.\n");
 202
 203                 ret = ab_control_default(abc);
 204                 if (ret < 0) {
 205                         free(abc);
 206                         return -ENODATA;
 207                 }
 208                 store_needed = true;
 209         }
 210
 211         if (abc->magic != BOOT_CTRL_MAGIC) {
 212                 log_err("ANDROID: Unknown A/B metadata: %.8x\n", abc->magic);
 213                 free(abc);
 214                 return -ENODATA;
 215         }
 216
 217         if (abc->version > BOOT_CTRL_VERSION) {
 218                 log_err("ANDROID: Unsupported A/B metadata version: %.8x\n",
 219                         abc->version);
 220                 free(abc);
 221                 return -ENODATA;
 222         }
 223
 224         /*
 225          * At this point a valid boot control metadata is stored in abc,
 226          * followed by other reserved data in the same block. We select a with
 227          * the higher priority slot that
 228          *  - is not marked as corrupted and
 229          *  - either has tries_remaining > 0 or successful_boot is true.
 230          * If the selected slot has a false successful_boot, we also decrement
 231          * the tries_remaining until it eventually becomes unbootable because
 232          * tries_remaining reaches 0. This mechanism produces a bootloader
 233          * induced rollback, typically right after a failed update.
 234          */
 235
 236         /* Safety check: limit the number of slots. */
 237         if (abc->nb_slot > ARRAY_SIZE(abc->slot_info)) {
 238                 abc->nb_slot = ARRAY_SIZE(abc->slot_info);
 239                 store_needed = true;
 240         }
 241
 242         slot = -1;
 243         for (i = 0; i < abc->nb_slot; ++i) {
 244                 if (abc->slot_info[i].verity_corrupted ||
 245                     !abc->slot_info[i].tries_remaining) {
 246                         log_debug("ANDROID: unbootable slot %d tries: %d, ",
 247                                   i, abc->slot_info[i].tries_remaining);
 248                         log_debug("corrupt: %d\n",
 249                                   abc->slot_info[i].verity_corrupted);
 250                         continue;
 251                 }
 252                 log_debug("ANDROID: bootable slot %d pri: %d, tries: %d, ",
 253                           i, abc->slot_info[i].priority,
 254                           abc->slot_info[i].tries_remaining);
 255                 log_debug("corrupt: %d, successful: %d\n",
 256                           abc->slot_info[i].verity_corrupted,
 257                           abc->slot_info[i].successful_boot);
 258
 259                 if (slot < 0 ||
 260                     ab_compare_slots(&abc->slot_info[i],
 261                                      &abc->slot_info[slot]) < 0) {
 262                         slot = i;
 263                 }
 264         }
 265
 266         if (slot >= 0 && !abc->slot_info[slot].successful_boot) {
 267                 log_err("ANDROID: Attempting slot %c, tries remaining %d\n",
 268                         BOOT_SLOT_NAME(slot),
 269                         abc->slot_info[slot].tries_remaining);
 270                 abc->slot_info[slot].tries_remaining--;
 271                 store_needed = true;
 272         }
 273
 274         if (slot >= 0) {
 275                 /*
 276                  * Legacy user-space requires this field to be set in the BCB.
 277                  * Newer releases load this slot suffix from the command line
 278                  * or the device tree.
 279                  */
 280                 memset(slot_suffix, 0, sizeof(slot_suffix));
 281                 slot_suffix[0] = BOOT_SLOT_NAME(slot);
 282                 if (memcmp(abc->slot_suffix, slot_suffix,
 283                            sizeof(slot_suffix))) {
 284                         memcpy(abc->slot_suffix, slot_suffix,
 285                                sizeof(slot_suffix));
 286                         store_needed = true;
 287                 }
 288         }
 289
 290         if (store_needed) {
 291                 abc->crc32_le = ab_control_compute_crc(abc);
 292                 ab_control_store(dev_desc, part_info, abc);
 293         }
 294         free(abc);
 295
 296         if (slot < 0)
 297                 return -EINVAL;
 298
 299         return slot;
 300 }