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common: Implement A/B metadata

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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>
This commit is contained in:
Ruslan Trofymenko 2019-07-05 15:37:32 +03:00 committed by Tom Rini
parent 6eccd1f740
commit d65e8da92e
4 changed files with 345 additions and 0 deletions
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10
common/Kconfig
View file

@ -821,6 +821,16 @@ config UPDATE_TFTP_MSEC_MAX
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"

1
common/Makefile
View file

@ -107,6 +107,7 @@ endif
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

300
common/android_ab.c Normal file
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@ -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;
}

34
include/android_ab.h Normal file
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@ -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 */