common: Implement A/B metadata
This patch determines the A/B-specific bootloader message structure
that is the basis for implementation of recovery and A/B update
functions. A/B metadata is stored in this structure and used to decide
which slot should we use to boot the device. Also some basic functions
for A/B metadata manipulation are implemented (like slot selection).
The patch was extracted from commits [1], [2] with some coding style
fixes.
[1] https://android-review.googlesource.com/c/platform/external/u-boot/+/729878/2
[2] https://android-review.googlesource.com/c/platform/external/u-boot/+/729880/2
Signed-off-by: Ruslan Trofymenko <ruslan.trofymenko@linaro.org>
Signed-off-by: Igor Opaniuk <igor.opaniuk@gmail.com>
Reviewed-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/common/Kconfig b/common/Kconfig
index 4865a4d..b556b59 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -821,6 +821,16 @@
default 100
depends on UPDATE_TFTP
+config ANDROID_AB
+ bool "Android A/B updates"
+ default n
+ help
+ If enabled, adds support for the new Android A/B update model. This
+ allows the bootloader to select which slot to boot from based on the
+ information provided by userspace via the Android boot_ctrl HAL. This
+ allows a bootloader to try a new version of the system but roll back
+ to previous version if the new one didn't boot all the way.
+
endmenu
menu "Blob list"
diff --git a/common/Makefile b/common/Makefile
index c7e41ef..302d8be 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -107,6 +107,7 @@
endif
obj-y += image.o
+obj-$(CONFIG_ANDROID_AB) += android_ab.o
obj-$(CONFIG_ANDROID_BOOT_IMAGE) += image-android.o
obj-$(CONFIG_$(SPL_TPL_)OF_LIBFDT) += image-fdt.o
obj-$(CONFIG_$(SPL_TPL_)FIT) += image-fit.o
diff --git a/common/android_ab.c b/common/android_ab.c
new file mode 100644
index 0000000..05ffc6f
--- /dev/null
+++ b/common/android_ab.c
@@ -0,0 +1,300 @@
+// SPDX-License-Identifier: BSD-2-Clause
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ */
+#include <common.h>
+#include <android_ab.h>
+#include <android_bootloader_message.h>
+#include <linux/err.h>
+#include <memalign.h>
+#include <u-boot/crc.h>
+
+/**
+ * Compute the CRC-32 of the bootloader control struct.
+ *
+ * Only the bytes up to the crc32_le field are considered for the CRC-32
+ * calculation.
+ *
+ * @param[in] abc bootloader control block
+ *
+ * @return crc32 sum
+ */
+static uint32_t ab_control_compute_crc(struct bootloader_control *abc)
+{
+ return crc32(0, (void *)abc, offsetof(typeof(*abc), crc32_le));
+}
+
+/**
+ * Initialize bootloader_control to the default value.
+ *
+ * It allows us to boot all slots in order from the first one. This value
+ * should be used when the bootloader message is corrupted, but not when
+ * a valid message indicates that all slots are unbootable.
+ *
+ * @param[in] abc bootloader control block
+ *
+ * @return 0 on success and a negative on error
+ */
+static int ab_control_default(struct bootloader_control *abc)
+{
+ int i;
+ const struct slot_metadata metadata = {
+ .priority = 15,
+ .tries_remaining = 7,
+ .successful_boot = 0,
+ .verity_corrupted = 0,
+ .reserved = 0
+ };
+
+ if (!abc)
+ return -EFAULT;
+
+ memcpy(abc->slot_suffix, "a\0\0\0", 4);
+ abc->magic = BOOT_CTRL_MAGIC;
+ abc->version = BOOT_CTRL_VERSION;
+ abc->nb_slot = NUM_SLOTS;
+ memset(abc->reserved0, 0, sizeof(abc->reserved0));
+ for (i = 0; i < abc->nb_slot; ++i)
+ abc->slot_info[i] = metadata;
+
+ memset(abc->reserved1, 0, sizeof(abc->reserved1));
+ abc->crc32_le = ab_control_compute_crc(abc);
+
+ return 0;
+}
+
+/**
+ * Load the boot_control struct from disk into newly allocated memory.
+ *
+ * This function allocates and returns an integer number of disk blocks,
+ * based on the block size of the passed device to help performing a
+ * read-modify-write operation on the boot_control struct.
+ * The boot_control struct offset (2 KiB) must be a multiple of the device
+ * block size, for simplicity.
+ *
+ * @param[in] dev_desc Device where to read the boot_control struct from
+ * @param[in] part_info Partition in 'dev_desc' where to read from, normally
+ * the "misc" partition should be used
+ * @param[out] pointer to pointer to bootloader_control data
+ * @return 0 on success and a negative on error
+ */
+static int ab_control_create_from_disk(struct blk_desc *dev_desc,
+ const disk_partition_t *part_info,
+ struct bootloader_control **abc)
+{
+ ulong abc_offset, abc_blocks, ret;
+
+ abc_offset = offsetof(struct bootloader_message_ab, slot_suffix);
+ if (abc_offset % part_info->blksz) {
+ log_err("ANDROID: Boot control block not block aligned.\n");
+ return -EINVAL;
+ }
+ abc_offset /= part_info->blksz;
+
+ abc_blocks = DIV_ROUND_UP(sizeof(struct bootloader_control),
+ part_info->blksz);
+ if (abc_offset + abc_blocks > part_info->size) {
+ log_err("ANDROID: boot control partition too small. Need at");
+ log_err(" least %lu blocks but have %lu blocks.\n",
+ abc_offset + abc_blocks, part_info->size);
+ return -EINVAL;
+ }
+ *abc = malloc_cache_aligned(abc_blocks * part_info->blksz);
+ if (!*abc)
+ return -ENOMEM;
+
+ ret = blk_dread(dev_desc, part_info->start + abc_offset, abc_blocks,
+ *abc);
+ if (IS_ERR_VALUE(ret)) {
+ log_err("ANDROID: Could not read from boot ctrl partition\n");
+ free(*abc);
+ return -EIO;
+ }
+
+ log_debug("ANDROID: Loaded ABC, %lu blocks\n", abc_blocks);
+
+ return 0;
+}
+
+/**
+ * Store the loaded boot_control block.
+ *
+ * Store back to the same location it was read from with
+ * ab_control_create_from_misc().
+ *
+ * @param[in] dev_desc Device where we should write the boot_control struct
+ * @param[in] part_info Partition on the 'dev_desc' where to write
+ * @param[in] abc Pointer to the boot control struct and the extra bytes after
+ * it up to the nearest block boundary
+ * @return 0 on success and a negative on error
+ */
+static int ab_control_store(struct blk_desc *dev_desc,
+ const disk_partition_t *part_info,
+ struct bootloader_control *abc)
+{
+ ulong abc_offset, abc_blocks, ret;
+
+ abc_offset = offsetof(struct bootloader_message_ab, slot_suffix) /
+ part_info->blksz;
+ abc_blocks = DIV_ROUND_UP(sizeof(struct bootloader_control),
+ part_info->blksz);
+ ret = blk_dwrite(dev_desc, part_info->start + abc_offset, abc_blocks,
+ abc);
+ if (IS_ERR_VALUE(ret)) {
+ log_err("ANDROID: Could not write back the misc partition\n");
+ return -EIO;
+ }
+
+ return 0;
+}
+
+/**
+ * Compare two slots.
+ *
+ * The function determines slot which is should we boot from among the two.
+ *
+ * @param[in] a The first bootable slot metadata
+ * @param[in] b The second bootable slot metadata
+ * @return Negative if the slot "a" is better, positive of the slot "b" is
+ * better or 0 if they are equally good.
+ */
+static int ab_compare_slots(const struct slot_metadata *a,
+ const struct slot_metadata *b)
+{
+ /* Higher priority is better */
+ if (a->priority != b->priority)
+ return b->priority - a->priority;
+
+ /* Higher successful_boot value is better, in case of same priority */
+ if (a->successful_boot != b->successful_boot)
+ return b->successful_boot - a->successful_boot;
+
+ /* Higher tries_remaining is better to ensure round-robin */
+ if (a->tries_remaining != b->tries_remaining)
+ return b->tries_remaining - a->tries_remaining;
+
+ return 0;
+}
+
+int ab_select_slot(struct blk_desc *dev_desc, disk_partition_t *part_info)
+{
+ struct bootloader_control *abc = NULL;
+ u32 crc32_le;
+ int slot, i, ret;
+ bool store_needed = false;
+ char slot_suffix[4];
+
+ ret = ab_control_create_from_disk(dev_desc, part_info, &abc);
+ if (ret < 0) {
+ /*
+ * This condition represents an actual problem with the code or
+ * the board setup, like an invalid partition information.
+ * Signal a repair mode and do not try to boot from either slot.
+ */
+ return ret;
+ }
+
+ crc32_le = ab_control_compute_crc(abc);
+ if (abc->crc32_le != crc32_le) {
+ log_err("ANDROID: Invalid CRC-32 (expected %.8x, found %.8x),",
+ crc32_le, abc->crc32_le);
+ log_err("re-initializing A/B metadata.\n");
+
+ ret = ab_control_default(abc);
+ if (ret < 0) {
+ free(abc);
+ return -ENODATA;
+ }
+ store_needed = true;
+ }
+
+ if (abc->magic != BOOT_CTRL_MAGIC) {
+ log_err("ANDROID: Unknown A/B metadata: %.8x\n", abc->magic);
+ free(abc);
+ return -ENODATA;
+ }
+
+ if (abc->version > BOOT_CTRL_VERSION) {
+ log_err("ANDROID: Unsupported A/B metadata version: %.8x\n",
+ abc->version);
+ free(abc);
+ return -ENODATA;
+ }
+
+ /*
+ * At this point a valid boot control metadata is stored in abc,
+ * followed by other reserved data in the same block. We select a with
+ * the higher priority slot that
+ * - is not marked as corrupted and
+ * - either has tries_remaining > 0 or successful_boot is true.
+ * If the selected slot has a false successful_boot, we also decrement
+ * the tries_remaining until it eventually becomes unbootable because
+ * tries_remaining reaches 0. This mechanism produces a bootloader
+ * induced rollback, typically right after a failed update.
+ */
+
+ /* Safety check: limit the number of slots. */
+ if (abc->nb_slot > ARRAY_SIZE(abc->slot_info)) {
+ abc->nb_slot = ARRAY_SIZE(abc->slot_info);
+ store_needed = true;
+ }
+
+ slot = -1;
+ for (i = 0; i < abc->nb_slot; ++i) {
+ if (abc->slot_info[i].verity_corrupted ||
+ !abc->slot_info[i].tries_remaining) {
+ log_debug("ANDROID: unbootable slot %d tries: %d, ",
+ i, abc->slot_info[i].tries_remaining);
+ log_debug("corrupt: %d\n",
+ abc->slot_info[i].verity_corrupted);
+ continue;
+ }
+ log_debug("ANDROID: bootable slot %d pri: %d, tries: %d, ",
+ i, abc->slot_info[i].priority,
+ abc->slot_info[i].tries_remaining);
+ log_debug("corrupt: %d, successful: %d\n",
+ abc->slot_info[i].verity_corrupted,
+ abc->slot_info[i].successful_boot);
+
+ if (slot < 0 ||
+ ab_compare_slots(&abc->slot_info[i],
+ &abc->slot_info[slot]) < 0) {
+ slot = i;
+ }
+ }
+
+ if (slot >= 0 && !abc->slot_info[slot].successful_boot) {
+ log_err("ANDROID: Attempting slot %c, tries remaining %d\n",
+ BOOT_SLOT_NAME(slot),
+ abc->slot_info[slot].tries_remaining);
+ abc->slot_info[slot].tries_remaining--;
+ store_needed = true;
+ }
+
+ if (slot >= 0) {
+ /*
+ * Legacy user-space requires this field to be set in the BCB.
+ * Newer releases load this slot suffix from the command line
+ * or the device tree.
+ */
+ memset(slot_suffix, 0, sizeof(slot_suffix));
+ slot_suffix[0] = BOOT_SLOT_NAME(slot);
+ if (memcmp(abc->slot_suffix, slot_suffix,
+ sizeof(slot_suffix))) {
+ memcpy(abc->slot_suffix, slot_suffix,
+ sizeof(slot_suffix));
+ store_needed = true;
+ }
+ }
+
+ if (store_needed) {
+ abc->crc32_le = ab_control_compute_crc(abc);
+ ab_control_store(dev_desc, part_info, abc);
+ }
+ free(abc);
+
+ if (slot < 0)
+ return -EINVAL;
+
+ return slot;
+}
diff --git a/include/android_ab.h b/include/android_ab.h
new file mode 100644
index 0000000..810906d
--- /dev/null
+++ b/include/android_ab.h
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ */
+
+#ifndef __ANDROID_AB_H
+#define __ANDROID_AB_H
+
+#include <common.h>
+
+/* Android standard boot slot names are 'a', 'b', 'c', ... */
+#define BOOT_SLOT_NAME(slot_num) ('a' + (slot_num))
+
+/* Number of slots */
+#define NUM_SLOTS 2
+
+/**
+ * Select the slot where to boot from.
+ *
+ * On Android devices with more than one boot slot (multiple copies of the
+ * kernel and system images) selects which slot should be used to boot from and
+ * registers the boot attempt. This is used in by the new A/B update model where
+ * one slot is updated in the background while running from the other slot. If
+ * the selected slot did not successfully boot in the past, a boot attempt is
+ * registered before returning from this function so it isn't selected
+ * indefinitely.
+ *
+ * @param[in] dev_desc Place to store the device description pointer
+ * @param[in] part_info Place to store the partition information
+ * @return The slot number (>= 0) on success, or a negative on error
+ */
+int ab_select_slot(struct blk_desc *dev_desc, disk_partition_t *part_info);
+
+#endif /* __ANDROID_AB_H */