[U-Boot] [PATCH v4 2/6] common: Implement A/B metadata
Igor Opaniuk
igor.opaniuk at gmail.com
Tue Jul 2 08:50:59 UTC 2019
From: Ruslan Trofymenko <ruslan.trofymenko at linaro.org>
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 at linaro.org>
Signed-off-by: Igor Opaniuk <igor.opaniuk at gmail.com>
Reviewed-by: Sam Protsenko <semen.protsenko at linaro.org>
Reviewed-by: Simon Glass <sjg at chromium.org>
---
Changes in v4:
* Removed android_bl_msg.h and re-used the one, which was
introduced by Eugeniu Rosca in [4] and [5].
* Initially we had intention to use "bcb" command and scripting for
providing proper boot sequence logic (slot selection, decrementing the
counter for each slot), but found out that it's better to keep using
a dedicated command ab_select to avoid huge amount of scripting in
the headers in includes/config for each platform.
* Remove ANDROID_ prefix for multiple macros
Changes in v3:
* Add multiple sanity checks
* Fix mix. minor code formatting issues
Changes in v2:
* Function return codes are clarified
* Some types and constants are renamed (for compactness)
* android_bootloader_message.h is renamed to android_bl_msg.h
* 'debug' calls are changed to 'log_debug'
* Order of headers is changed
* android_bl_msg.h was synced with AOSP master counterpart
common/Kconfig | 10 ++
common/Makefile | 1 +
common/android_ab.c | 298 +++++++++++++++++++++++++++++++++++++++++++
include/android_ab.h | 34 +++++
4 files changed, 343 insertions(+)
create mode 100644 common/android_ab.c
create mode 100644 include/android_ab.h
diff --git a/common/Kconfig b/common/Kconfig
index af66496e75..63287865ef 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -814,6 +814,16 @@ 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"
diff --git a/common/Makefile b/common/Makefile
index c7e41ef307..302d8beaf3 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -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
diff --git a/common/android_ab.c b/common/android_ab.c
new file mode 100644
index 0000000000..43a1ec8c37
--- /dev/null
+++ b/common/android_ab.c
@@ -0,0 +1,298 @@
+// 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;
+
+ 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;
+
+ if (blk_dread(dev_desc, part_info->start + abc_offset, abc_blocks,
+ *abc) != abc_blocks) {
+ 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;
+
+ abc_offset = offsetof(struct bootloader_message_ab, slot_suffix) /
+ part_info->blksz;
+ abc_blocks = DIV_ROUND_UP(sizeof(struct bootloader_control),
+ part_info->blksz);
+ if (blk_dwrite(dev_desc, part_info->start + abc_offset, abc_blocks,
+ abc) != abc_blocks) {
+ 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 0000000000..810906d22b
--- /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 */
--
2.17.1
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