drivers/md/dm-verity-chromeos.c - kernel/common - Git at Google

 /*
  * Copyright (C) 2010 The Chromium OS Authors <[email protected]>
  *                    All Rights Reserved.
  *
  * This file is released under the GPL.
  */
 /*
  * Implements a Chrome OS platform specific error handler.
  * When verity detects an invalid block, this error handling will
  * attempt to corrupt the kernel boot image. On reboot, the bios will
  * detect the kernel corruption and switch to the alternate kernel
  * and root file system partitions.
  *
  * Assumptions:
  * 1. Partitions are specified on the command line using uuid.
  * 2. The kernel partition is the partition number is one less
  *    than the root partition number.
  */
 #include <linux/bio.h>
 #include <linux/blkdev.h>
 #include <linux/crc32.h>
 #include <linux/device.h>
 #include <linux/device-mapper.h>
 #include <linux/efi.h>
 #include <linux/err.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/mount.h>
 #include <linux/notifier.h>
 #include <linux/string.h>
 #include <asm/page.h>

 #include "dm-verity.h"

 #define DM_MSG_PREFIX "verity-chromeos"
 #define DMVERROR "DMVERROR"

 #define GPT_TABLE_PAGE_NUM_ORDER 2
 #define GPT_TABLE_SIZE ((1 << GPT_TABLE_PAGE_NUM_ORDER) * 4096)

 struct gpt_header {
 	__le64 signature;
 	__le32 revision;
 	__le32 header_size;
 	__le32 header_crc32;
 	__le32 reserved1;
 	__le64 my_lba;
 	__le64 alternate_lba;
 	__le64 first_usable_lba;
 	__le64 last_usable_lba;
 	efi_guid_t disk_guid;
 	__le64 partition_entry_lba;
 	__le32 num_partition_entries;
 	__le32 sizeof_partition_entry;
 	__le32 partition_entry_array_crc32;

 	/* The rest of the logical block is reserved by UEFI and must be zero.
 	 * EFI standard handles this by:
 	 *
 	 * uint8_t		reserved2[ BlockSize - 92 ];
 	 */
 } __packed;

 struct chromeos_kernel_gpt_attributes {
 	u64 efi_spec:48;
 	u64 priority:4;
 	u64 tries:4;
 	u64 success:1;
 	u64 verity_error_counter:1;
 	u64 unused:6;
 } __packed;

 struct gpt_entry {
 	efi_guid_t partition_type_guid;
 	efi_guid_t unique_partition_guid;
 	__le64 starting_lba;
 	__le64 ending_lba;
 	struct chromeos_kernel_gpt_attributes attributes;
 	__le16 partition_name[72/sizeof(__le16)];
 } __packed;

 static void chromeos_invalidate_kernel_endio(struct bio *bio)
 {
 	if (bio->bi_status) {
 		DMERR("%s: bio operation failed (status=0x%x)", __func__,
 		      bio->bi_status);
 	}
 	complete(bio->bi_private);
 }

 static int chromeos_invalidate_kernel_submit(struct bio *bio,
 					     sector_t sector,
 					     unsigned int len_byte,
 					     struct page *page)
 {
 	DECLARE_COMPLETION_ONSTACK(wait);

 	bio->bi_private = &wait;
 	bio->bi_end_io = chromeos_invalidate_kernel_endio;

 	bio->bi_iter.bi_sector = sector;
 	bio->bi_vcnt = 1;
 	bio->bi_iter.bi_idx = 0;
 	bio->bi_iter.bi_size = len_byte;
 	bio->bi_iter.bi_bvec_done = 0;
 	bio->bi_io_vec[0].bv_page = page;
 	bio->bi_io_vec[0].bv_len = len_byte;
 	bio->bi_io_vec[0].bv_offset = 0;

 	submit_bio(bio);
 	/* Wait up to 2 seconds for completion or fail. */
 	if (!wait_for_completion_timeout(&wait, msecs_to_jiffies(2000)))
 		return -1;
 	return 0;
 }

 static dev_t get_boot_dev_from_root_dev(struct block_device *root_bdev)
 {
 	/* Very basic sanity checking. This should be better. */
 	if (!root_bdev || MAJOR(root_bdev->bd_dev) == 254 ||
 	    root_bdev->bd_partno <= 1) {
 		return 0;
 	}
 	return MKDEV(MAJOR(root_bdev->bd_dev), MINOR(root_bdev->bd_dev) - 1);
 }

 static char kern_guid[48];

 /*
  * get_boot_dev is based on dm_get_device_by_uuid in dm_bootcache.
  *
  * This function is marked __ref because it calls the __init marked
  * early_lookup_bdev when called from the early boot code.
  */
 static dev_t __ref get_boot_dev(void)
 {
 	const char partuuid[] = "PARTUUID=";
 	char uuid[sizeof(partuuid) + 36];
 	char *uuid_str;
 	dev_t devt;

 	if (!strlen(kern_guid)) {
 		DMERR("Couldn't get uuid, try root dev");
 		return 0;
 	}

 	if (strncmp(kern_guid, partuuid, strlen(partuuid))) {
 		/* Not prefixed with "PARTUUID=", so add it */
 		strcpy(uuid, partuuid);
 		strlcat(uuid, kern_guid, sizeof(uuid));
 		uuid_str = uuid;
 	} else {
 		uuid_str = kern_guid;
 	}
         if (early_lookup_bdev(uuid_str, &devt)) {
                 DMDEBUG("No matching partition for GUID: %s", uuid_str);
                 return 0;
         }
 	return devt;
 }

 /*
  * Invalidate the kernel which corresponds to the root block device.
  *
  * This function stamps DMVERROR on the beginning of the kernel partition.
  *
  * The kernel_guid commandline parameter is used to find the kernel partition
  *  number.
  * If that fails, the kernel partition is found by subtracting 1 from
  *  the root partition.
  * The DMVERROR string is stamped over only the CHROMEOS string at the
  *  beginning of the kernel blob, leaving the rest of it intact.
  */
 static int chromeos_invalidate_kernel_bio(struct block_device *root_bdev)
 {
 	int ret = 0;
 	struct block_device *bdev;
 	struct bio *bio;
 	struct page *page;
 	dev_t devt;
 	blk_mode_t dev_mode;

 	devt = get_boot_dev();
 	if (!devt) {
 		devt = get_boot_dev_from_root_dev(root_bdev);
 		if (!devt)
 			return -EINVAL;
 	}

 	/* First we open the device for reading. */
 	dev_mode = BLK_OPEN_READ | BLK_OPEN_EXCL;
 	bdev = blkdev_get_by_dev(devt, dev_mode,
 				 chromeos_invalidate_kernel_bio, NULL);
 	if (IS_ERR(bdev)) {
 		DMERR("invalidate_kernel: could not open device for reading");
 		dev_mode = 0;
 		ret = -1;
 		goto failed_to_read;
 	}

 	bio = bio_alloc(bdev, 1, REQ_OP_READ | REQ_SYNC, GFP_NOIO);
 	if (!bio) {
 		ret = -1;
 		goto failed_bio_alloc;
 	}

 	page = alloc_page(GFP_NOIO);
 	if (!page) {
 		ret = -ENOMEM;
 		goto failed_to_alloc_page;
 	}

 	if (bdev_logical_block_size(bdev) > page_size(page)) {
 		ret = -1;
 		goto failed_to_submit_read;
 	}

 	/*
 	 * Request read operation with REQ_PREFLUSH flag to ensure that the
 	 * cache of non-volatile storage device has been flushed before read is
 	 * started.
 	 */
 	if (chromeos_invalidate_kernel_submit(bio, 0,
 					      bdev_logical_block_size(bdev),
 					      page)) {
 		ret = -1;
 		goto failed_to_submit_read;
 	}

 	/* We have a page. Let's make sure it looks right. */
 	if (memcmp("CHROMEOS", page_address(page), 8)) {
 		DMERR("invalidate_kernel called on non-kernel partition");
 		ret = -EINVAL;
 		goto invalid_header;
 	} else {
 		DMERR("invalidate_kernel: found CHROMEOS kernel partition");
 	}

 	/* Stamp it and rewrite */
 	memcpy(page_address(page), DMVERROR, strlen(DMVERROR));

 	/* The block dev was being changed on read. Let's reopen here. */
 	blkdev_put(bdev, chromeos_invalidate_kernel_bio);
 	dev_mode = BLK_OPEN_WRITE | BLK_OPEN_EXCL;
 	bdev = blkdev_get_by_dev(devt, dev_mode,
 				 chromeos_invalidate_kernel_bio, NULL);
 	if (IS_ERR(bdev)) {
 		DMERR("invalidate_kernel: could not open device for writing");
 		dev_mode = 0;
 		ret = -1;
 		goto failed_to_write;
 	}

 	/* We re-use the same bio to do the write after the read. Need to reset
 	 * it to initialize bio->bi_remaining.
 	 */
 	bio_reset(bio, bdev, REQ_OP_WRITE | REQ_SYNC | REQ_FUA);

 	/*
 	 * Request write operation with REQ_FUA flag to ensure that I/O
 	 * completion for the write is signaled only after the data has been
 	 * committed to non-volatile storage.
 	 */
 	if (chromeos_invalidate_kernel_submit(bio, 0,
 					      bdev_logical_block_size(bdev),
 					      page)) {
 		ret = -1;
 		goto failed_to_submit_write;
 	}

 	DMERR("invalidate_kernel: completed.");
 	ret = 0;
 failed_to_submit_write:
 failed_to_write:
 invalid_header:
 	__free_page(page);
 failed_to_submit_read:
 	/* Technically, we'll leak a page with the pending bio, but
 	 *  we're about to panic so it's safer to do the panic() we expect.
 	 */
 failed_to_alloc_page:
 	bio_put(bio);
 failed_bio_alloc:
 	if (dev_mode)
 		blkdev_put(bdev, chromeos_invalidate_kernel_bio);
 failed_to_read:
 	return ret;
 }

 static inline __le32
 efi_crc32(const void *buf, unsigned long len)
 {
 	return cpu_to_le32(crc32(~0L, buf, len) ^ ~0L);
 }

 static int chromeos_gpt_io_submit(struct bio *bio,
 				  struct block_device *bdev,
 				  unsigned int op,
 				  unsigned int op_flags,
 				  sector_t hdr_lba,
 				  struct page *hdr_page,
 				  struct page *tbl_pages)
 {
 	size_t block_size = bdev_logical_block_size(bdev);
 	size_t sectors_per_lba = block_size >> SECTOR_SHIFT;
 	int tbl_sector;
 	struct gpt_header *header;

 	if (bdev_logical_block_size(bdev) > page_size(hdr_page))
 		return -1;

 	bio_reset(bio, bdev, op | op_flags);
 	if (chromeos_invalidate_kernel_submit(bio,
 					      hdr_lba * sectors_per_lba,
 					      block_size,
 					      hdr_page)) {
 		return  -1;
 	}

 	header = page_address(hdr_page);
 	tbl_sector = le64_to_cpu(header->partition_entry_lba) * sectors_per_lba;

 	bio_reset(bio, bdev, op | op_flags);
 	if (chromeos_invalidate_kernel_submit(bio,
 					      tbl_sector,
 					      GPT_TABLE_SIZE,
 					      tbl_pages)) {
 		return  -1;
 	}

 	return 0;
 }

 static int chromeos_increment_gpt_err_count(struct page *hdr_page,
 					    struct page *tbl_pages,
 					    u8 active_gpt_entry_id)
 {
 	struct gpt_header *header = page_address(hdr_page);
 	struct gpt_entry *entries = page_address(tbl_pages);
 	struct gpt_entry *active_entry = &entries[active_gpt_entry_id];
 	u64 gpt_table_size =
 		(u64)le32_to_cpu(header->num_partition_entries) *
 		le32_to_cpu(header->sizeof_partition_entry);

 	if (gpt_table_size > GPT_TABLE_SIZE)
 		return -1;

 	if (active_entry->attributes.verity_error_counter == 1)
 		return -1;

 	active_entry->attributes.verity_error_counter = 1;
 	header->partition_entry_array_crc32 =
 		efi_crc32((const unsigned char *) (entries),
 		gpt_table_size);
 	header->header_crc32 = 0;
 	header->header_crc32 = efi_crc32((const unsigned char *) (header),
 		le32_to_cpu(header->header_size));

 	return 0;
 }

 static int chromeos_handle_retries(struct bio *bio,
 				   dev_t devt,
 				   u8 active_gpt_entry_id,
 				   sector_t hdr_lba,
 				   struct page *hdr_page,
 				   struct page *tbl_pages)
 {
 	struct block_device *bdev;
 	fmode_t dev_mode = 0;
 	int ret = 0;

 	dev_mode = FMODE_READ;
 	bdev = blkdev_get_by_dev(devt, dev_mode,
 				 chromeos_handle_retries, NULL);
 	if (IS_ERR(bdev)) {
 		DMERR("update_tries: could not open device for reading: %ld",
 		      PTR_ERR(bdev));
 		dev_mode = 0;
 		ret = -1;
 		goto failed;
 	}

 	/*
 	 * Request read operation with REQ_PREFLUSH flag to ensure that the
 	 * cache of non-volatile storage device has been flushed before read is
 	 * started.
 	 */
 	if (chromeos_gpt_io_submit(bio, bdev, REQ_OP_READ,
 				   REQ_SYNC | REQ_PREFLUSH, hdr_lba,
 				   hdr_page, tbl_pages)) {
 		DMERR("update_tries: failed reading %s GPT",
 		      hdr_lba == 1 ? "primary" : "secondary");
 		ret = -1;
 		goto failed;
 	}

 	if (chromeos_increment_gpt_err_count(hdr_page, tbl_pages,
 					     active_gpt_entry_id)) {
 		DMERR("update_tries: retries exceeded");
 		ret = -1;
 		goto failed;
 	}

 	/* The block dev was being changed on read. Let's reopen here. */
 	blkdev_put(bdev, chromeos_handle_retries);
 	dev_mode = FMODE_WRITE;
 	bdev = blkdev_get_by_dev(devt, dev_mode,
 				 chromeos_handle_retries, NULL);
 	if (IS_ERR(bdev)) {
 		DMERR("update_tries: could not open device for writing");
 		dev_mode = 0;
 		ret = -1;
 		goto failed;
 	}

 	/*
 	 * Request write operation with REQ_FUA flag to ensure that I/O
 	 * completion for the write is signaled only after the data has been
 	 * committed to non-volatile storage.
 	 */
 	if (chromeos_gpt_io_submit(bio, bdev, REQ_OP_WRITE,
 				   REQ_SYNC | REQ_FUA, hdr_lba,
 				   hdr_page, tbl_pages)) {
 		DMERR("update_tries: failed writing %s GPT",
 		      hdr_lba == 1 ? "primary" : "secondary");
 		ret = -1;
 		goto failed;
 	}

 failed:
 	if (dev_mode)
 		blkdev_put(bdev, chromeos_handle_retries);

 	if (!ret)
 		DMERR("update_tries: updated %s GPT",
 		      hdr_lba == 1 ? "primary" : "secondary");

 	return ret;
 }

 static int chromeos_update_tries(struct block_device *root_bdev)
 {
 	int ret = 0;
 	struct bio *bio;
 	struct page *hdr_page = NULL;
 	struct page *tbl_pages = NULL;
 	struct gpt_header *header;
 	dev_t gpt_devt =
 		disk_devt(dev_to_disk(&root_bdev->bd_disk->part0->bd_device));
 	dev_t kernel_devt =
 		get_boot_dev() ?: get_boot_dev_from_root_dev(root_bdev);
 	struct block_device *kernel_bdev;
 	u8 kernel_gpt_entry_id;

 	if (!gpt_devt)
 		return -EINVAL;

 	/* Get block device to get the partno. */
 	kernel_bdev = blkdev_get_by_dev(kernel_devt, FMODE_READ,
 				 chromeos_update_tries, NULL);
 	if (IS_ERR(kernel_bdev))
 		return PTR_ERR(kernel_bdev);
 	/*
 	 * GPT entry offset is 0 based, and partno, represented by MINOR,
 	 * is 1 based, so subtract 1.
 	 */
 	kernel_gpt_entry_id = kernel_bdev->bd_partno - 1;
 	blkdev_put(kernel_bdev, chromeos_update_tries);

 	bio = bio_alloc(root_bdev, 1, 0, GFP_NOIO);
 	if (!bio) {
 		ret = -1;
 		goto failed_bio_alloc;
 	}

 	hdr_page = alloc_page(GFP_NOIO);
 	tbl_pages = alloc_pages(GFP_NOIO, GPT_TABLE_PAGE_NUM_ORDER);
 	if (!hdr_page || !tbl_pages) {
 		ret = -ENOMEM;
 		goto failed;
 	}

 	header = page_address(hdr_page);

 	if (chromeos_handle_retries(bio, gpt_devt, kernel_gpt_entry_id, 1,
 				    hdr_page, tbl_pages) ||
 	    chromeos_handle_retries(bio, gpt_devt, kernel_gpt_entry_id,
 				    le64_to_cpu(header->alternate_lba),
 				    hdr_page, tbl_pages)) {
 		DMERR("update_tries: retry failed, will invalidated kernel");
 		ret = -1;
 		goto failed;
 	}

 	DMERR("update_tries: completed");
 	ret = 0;
 failed:
 	if (hdr_page)
 		__free_page(hdr_page);
 	if (tbl_pages)
 		__free_pages(tbl_pages, GPT_TABLE_PAGE_NUM_ORDER);
 	bio_put(bio);
 failed_bio_alloc:
 	return ret;
 }

 static int error_handler(struct notifier_block *nb, unsigned long transient,
 			 void *opaque_err)
 {
 	struct dm_verity_error_state *err =
 		(struct dm_verity_error_state *) opaque_err;
 	err->behavior = DM_VERITY_ERROR_BEHAVIOR_PANIC;
 	if (transient)
 		return 0;

 	// Do not invalidate kernel if successfully updated try count.
 	if (!chromeos_update_tries(err->dev))
 		return 0;

 	/* Mark the kernel partition as invalid. */
 	chromeos_invalidate_kernel_bio(err->dev);
 	return 0;
 }

 static struct notifier_block chromeos_nb = {
 	.notifier_call = &error_handler,
 	.next = NULL,
 	.priority = 1,
 };

 static int __init dm_verity_chromeos_init(void)
 {
 	int r;

 	r = dm_verity_register_error_notifier(&chromeos_nb);
 	if (r < 0)
 		DMERR("failed to register handler: %d", r);
 	else
 		DMINFO("dm-verity-chromeos registered");
 	return r;
 }

 static void __exit dm_verity_chromeos_exit(void)
 {
 	dm_verity_unregister_error_notifier(&chromeos_nb);
 }

 module_init(dm_verity_chromeos_init);
 module_exit(dm_verity_chromeos_exit);

 MODULE_AUTHOR("Will Drewry <[email protected]>");
 MODULE_DESCRIPTION("chromeos-specific error handler for dm-verity");
 MODULE_LICENSE("GPL");

 /* Declare parameter with no module prefix */
 #undef MODULE_PARAM_PREFIX
 #define MODULE_PARAM_PREFIX	""
 module_param_string(kern_guid, kern_guid, sizeof(kern_guid), 0);
	/*
	* Copyright (C) 2010 The Chromium OS Authors <[email protected]>
	* All Rights Reserved.
	*
	* This file is released under the GPL.
	*/
	/*
	* Implements a Chrome OS platform specific error handler.
	* When verity detects an invalid block, this error handling will
	* attempt to corrupt the kernel boot image. On reboot, the bios will
	* detect the kernel corruption and switch to the alternate kernel
	* and root file system partitions.
	*
	* Assumptions:
	* 1. Partitions are specified on the command line using uuid.
	* 2. The kernel partition is the partition number is one less
	* than the root partition number.
	*/
	#include <linux/bio.h>
	#include <linux/blkdev.h>
	#include <linux/crc32.h>
	#include <linux/device.h>
	#include <linux/device-mapper.h>
	#include <linux/efi.h>
	#include <linux/err.h>
	#include <linux/kernel.h>
	#include <linux/mm.h>
	#include <linux/module.h>
	#include <linux/mount.h>
	#include <linux/notifier.h>
	#include <linux/string.h>
	#include <asm/page.h>

	#include "dm-verity.h"

	#define DM_MSG_PREFIX "verity-chromeos"
	#define DMVERROR "DMVERROR"

	#define GPT_TABLE_PAGE_NUM_ORDER 2
	#define GPT_TABLE_SIZE ((1 << GPT_TABLE_PAGE_NUM_ORDER) * 4096)

	struct gpt_header {
	__le64 signature;
	__le32 revision;
	__le32 header_size;
	__le32 header_crc32;
	__le32 reserved1;
	__le64 my_lba;
	__le64 alternate_lba;
	__le64 first_usable_lba;
	__le64 last_usable_lba;
	efi_guid_t disk_guid;
	__le64 partition_entry_lba;
	__le32 num_partition_entries;
	__le32 sizeof_partition_entry;
	__le32 partition_entry_array_crc32;

	/* The rest of the logical block is reserved by UEFI and must be zero.
	* EFI standard handles this by:
	*
	* uint8_t reserved2[ BlockSize - 92 ];
	*/
	} __packed;

	struct chromeos_kernel_gpt_attributes {
	u64 efi_spec:48;
	u64 priority:4;
	u64 tries:4;
	u64 success:1;
	u64 verity_error_counter:1;
	u64 unused:6;
	} __packed;

	struct gpt_entry {
	efi_guid_t partition_type_guid;
	efi_guid_t unique_partition_guid;
	__le64 starting_lba;
	__le64 ending_lba;
	struct chromeos_kernel_gpt_attributes attributes;
	__le16 partition_name[72/sizeof(__le16)];
	} __packed;

	static void chromeos_invalidate_kernel_endio(struct bio *bio)
	{
	if (bio->bi_status) {
	DMERR("%s: bio operation failed (status=0x%x)", __func__,
	bio->bi_status);
	}
	complete(bio->bi_private);
	}

	static int chromeos_invalidate_kernel_submit(struct bio *bio,
	sector_t sector,
	unsigned int len_byte,
	struct page *page)
	{
	DECLARE_COMPLETION_ONSTACK(wait);

	bio->bi_private = &wait;
	bio->bi_end_io = chromeos_invalidate_kernel_endio;

	bio->bi_iter.bi_sector = sector;
	bio->bi_vcnt = 1;
	bio->bi_iter.bi_idx = 0;
	bio->bi_iter.bi_size = len_byte;
	bio->bi_iter.bi_bvec_done = 0;
	bio->bi_io_vec[0].bv_page = page;
	bio->bi_io_vec[0].bv_len = len_byte;
	bio->bi_io_vec[0].bv_offset = 0;

	submit_bio(bio);
	/* Wait up to 2 seconds for completion or fail. */
	if (!wait_for_completion_timeout(&wait, msecs_to_jiffies(2000)))
	return -1;
	return 0;
	}

	static dev_t get_boot_dev_from_root_dev(struct block_device *root_bdev)
	{
	/* Very basic sanity checking. This should be better. */
	if (!root_bdev \|\| MAJOR(root_bdev->bd_dev) == 254 \|\|
	root_bdev->bd_partno <= 1) {
	return 0;
	}
	return MKDEV(MAJOR(root_bdev->bd_dev), MINOR(root_bdev->bd_dev) - 1);
	}

	static char kern_guid[48];

	/*
	* get_boot_dev is based on dm_get_device_by_uuid in dm_bootcache.
	*
	* This function is marked __ref because it calls the __init marked
	* early_lookup_bdev when called from the early boot code.
	*/
	static dev_t __ref get_boot_dev(void)
	{
	const char partuuid[] = "PARTUUID=";
	char uuid[sizeof(partuuid) + 36];
	char *uuid_str;
	dev_t devt;

	if (!strlen(kern_guid)) {
	DMERR("Couldn't get uuid, try root dev");
	return 0;
	}

	if (strncmp(kern_guid, partuuid, strlen(partuuid))) {
	/* Not prefixed with "PARTUUID=", so add it */
	strcpy(uuid, partuuid);
	strlcat(uuid, kern_guid, sizeof(uuid));
	uuid_str = uuid;
	} else {
	uuid_str = kern_guid;
	}
	if (early_lookup_bdev(uuid_str, &devt)) {
	DMDEBUG("No matching partition for GUID: %s", uuid_str);
	return 0;
	}
	return devt;
	}

	/*
	* Invalidate the kernel which corresponds to the root block device.
	*
	* This function stamps DMVERROR on the beginning of the kernel partition.
	*
	* The kernel_guid commandline parameter is used to find the kernel partition
	* number.
	* If that fails, the kernel partition is found by subtracting 1 from
	* the root partition.
	* The DMVERROR string is stamped over only the CHROMEOS string at the
	* beginning of the kernel blob, leaving the rest of it intact.
	*/
	static int chromeos_invalidate_kernel_bio(struct block_device *root_bdev)
	{
	int ret = 0;
	struct block_device *bdev;
	struct bio *bio;
	struct page *page;
	dev_t devt;
	blk_mode_t dev_mode;

	devt = get_boot_dev();
	if (!devt) {
	devt = get_boot_dev_from_root_dev(root_bdev);
	if (!devt)
	return -EINVAL;
	}

	/* First we open the device for reading. */
	dev_mode = BLK_OPEN_READ \| BLK_OPEN_EXCL;
	bdev = blkdev_get_by_dev(devt, dev_mode,
	chromeos_invalidate_kernel_bio, NULL);
	if (IS_ERR(bdev)) {
	DMERR("invalidate_kernel: could not open device for reading");
	dev_mode = 0;
	ret = -1;
	goto failed_to_read;
	}

	bio = bio_alloc(bdev, 1, REQ_OP_READ \| REQ_SYNC, GFP_NOIO);
	if (!bio) {
	ret = -1;
	goto failed_bio_alloc;
	}

	page = alloc_page(GFP_NOIO);
	if (!page) {
	ret = -ENOMEM;
	goto failed_to_alloc_page;
	}

	if (bdev_logical_block_size(bdev) > page_size(page)) {
	ret = -1;
	goto failed_to_submit_read;
	}

	/*
	* Request read operation with REQ_PREFLUSH flag to ensure that the
	* cache of non-volatile storage device has been flushed before read is
	* started.
	*/
	if (chromeos_invalidate_kernel_submit(bio, 0,
	bdev_logical_block_size(bdev),
	page)) {
	ret = -1;
	goto failed_to_submit_read;
	}

	/* We have a page. Let's make sure it looks right. */
	if (memcmp("CHROMEOS", page_address(page), 8)) {
	DMERR("invalidate_kernel called on non-kernel partition");
	ret = -EINVAL;
	goto invalid_header;
	} else {
	DMERR("invalidate_kernel: found CHROMEOS kernel partition");
	}

	/* Stamp it and rewrite */
	memcpy(page_address(page), DMVERROR, strlen(DMVERROR));

	/* The block dev was being changed on read. Let's reopen here. */
	blkdev_put(bdev, chromeos_invalidate_kernel_bio);
	dev_mode = BLK_OPEN_WRITE \| BLK_OPEN_EXCL;
	bdev = blkdev_get_by_dev(devt, dev_mode,
	chromeos_invalidate_kernel_bio, NULL);
	if (IS_ERR(bdev)) {
	DMERR("invalidate_kernel: could not open device for writing");
	dev_mode = 0;
	ret = -1;
	goto failed_to_write;
	}

	/* We re-use the same bio to do the write after the read. Need to reset
	* it to initialize bio->bi_remaining.
	*/
	bio_reset(bio, bdev, REQ_OP_WRITE \| REQ_SYNC \| REQ_FUA);

	/*
	* Request write operation with REQ_FUA flag to ensure that I/O
	* completion for the write is signaled only after the data has been
	* committed to non-volatile storage.
	*/
	if (chromeos_invalidate_kernel_submit(bio, 0,
	bdev_logical_block_size(bdev),
	page)) {
	ret = -1;
	goto failed_to_submit_write;
	}

	DMERR("invalidate_kernel: completed.");
	ret = 0;
	failed_to_submit_write:
	failed_to_write:
	invalid_header:
	__free_page(page);
	failed_to_submit_read:
	/* Technically, we'll leak a page with the pending bio, but
	* we're about to panic so it's safer to do the panic() we expect.
	*/
	failed_to_alloc_page:
	bio_put(bio);
	failed_bio_alloc:
	if (dev_mode)
	blkdev_put(bdev, chromeos_invalidate_kernel_bio);
	failed_to_read:
	return ret;
	}

	static inline __le32
	efi_crc32(const void *buf, unsigned long len)
	{
	return cpu_to_le32(crc32(~0L, buf, len) ^ ~0L);
	}

	static int chromeos_gpt_io_submit(struct bio *bio,
	struct block_device *bdev,
	unsigned int op,
	unsigned int op_flags,
	sector_t hdr_lba,
	struct page *hdr_page,
	struct page *tbl_pages)
	{
	size_t block_size = bdev_logical_block_size(bdev);
	size_t sectors_per_lba = block_size >> SECTOR_SHIFT;
	int tbl_sector;
	struct gpt_header *header;

	if (bdev_logical_block_size(bdev) > page_size(hdr_page))
	return -1;

	bio_reset(bio, bdev, op \| op_flags);
	if (chromeos_invalidate_kernel_submit(bio,
	hdr_lba * sectors_per_lba,
	block_size,
	hdr_page)) {
	return -1;
	}

	header = page_address(hdr_page);
	tbl_sector = le64_to_cpu(header->partition_entry_lba) * sectors_per_lba;

	bio_reset(bio, bdev, op \| op_flags);
	if (chromeos_invalidate_kernel_submit(bio,
	tbl_sector,
	GPT_TABLE_SIZE,
	tbl_pages)) {
	return -1;
	}

	return 0;
	}

	static int chromeos_increment_gpt_err_count(struct page *hdr_page,
	struct page *tbl_pages,
	u8 active_gpt_entry_id)
	{
	struct gpt_header *header = page_address(hdr_page);
	struct gpt_entry *entries = page_address(tbl_pages);
	struct gpt_entry *active_entry = &entries[active_gpt_entry_id];
	u64 gpt_table_size =
	(u64)le32_to_cpu(header->num_partition_entries) *
	le32_to_cpu(header->sizeof_partition_entry);

	if (gpt_table_size > GPT_TABLE_SIZE)
	return -1;

	if (active_entry->attributes.verity_error_counter == 1)
	return -1;

	active_entry->attributes.verity_error_counter = 1;
	header->partition_entry_array_crc32 =
	efi_crc32((const unsigned char *) (entries),
	gpt_table_size);
	header->header_crc32 = 0;
	header->header_crc32 = efi_crc32((const unsigned char *) (header),
	le32_to_cpu(header->header_size));

	return 0;
	}

	static int chromeos_handle_retries(struct bio *bio,
	dev_t devt,
	u8 active_gpt_entry_id,
	sector_t hdr_lba,
	struct page *hdr_page,
	struct page *tbl_pages)
	{
	struct block_device *bdev;
	fmode_t dev_mode = 0;
	int ret = 0;

	dev_mode = FMODE_READ;
	bdev = blkdev_get_by_dev(devt, dev_mode,
	chromeos_handle_retries, NULL);
	if (IS_ERR(bdev)) {
	DMERR("update_tries: could not open device for reading: %ld",
	PTR_ERR(bdev));
	dev_mode = 0;
	ret = -1;
	goto failed;
	}

	/*
	* Request read operation with REQ_PREFLUSH flag to ensure that the
	* cache of non-volatile storage device has been flushed before read is
	* started.
	*/
	if (chromeos_gpt_io_submit(bio, bdev, REQ_OP_READ,
	REQ_SYNC \| REQ_PREFLUSH, hdr_lba,
	hdr_page, tbl_pages)) {
	DMERR("update_tries: failed reading %s GPT",
	hdr_lba == 1 ? "primary" : "secondary");
	ret = -1;
	goto failed;
	}

	if (chromeos_increment_gpt_err_count(hdr_page, tbl_pages,
	active_gpt_entry_id)) {
	DMERR("update_tries: retries exceeded");
	ret = -1;
	goto failed;
	}

	/* The block dev was being changed on read. Let's reopen here. */
	blkdev_put(bdev, chromeos_handle_retries);
	dev_mode = FMODE_WRITE;
	bdev = blkdev_get_by_dev(devt, dev_mode,
	chromeos_handle_retries, NULL);
	if (IS_ERR(bdev)) {
	DMERR("update_tries: could not open device for writing");
	dev_mode = 0;
	ret = -1;
	goto failed;
	}

	/*
	* Request write operation with REQ_FUA flag to ensure that I/O
	* completion for the write is signaled only after the data has been
	* committed to non-volatile storage.
	*/
	if (chromeos_gpt_io_submit(bio, bdev, REQ_OP_WRITE,
	REQ_SYNC \| REQ_FUA, hdr_lba,
	hdr_page, tbl_pages)) {
	DMERR("update_tries: failed writing %s GPT",
	hdr_lba == 1 ? "primary" : "secondary");
	ret = -1;
	goto failed;
	}

	failed:
	if (dev_mode)
	blkdev_put(bdev, chromeos_handle_retries);

	if (!ret)
	DMERR("update_tries: updated %s GPT",
	hdr_lba == 1 ? "primary" : "secondary");

	return ret;
	}

	static int chromeos_update_tries(struct block_device *root_bdev)
	{
	int ret = 0;
	struct bio *bio;
	struct page *hdr_page = NULL;
	struct page *tbl_pages = NULL;
	struct gpt_header *header;
	dev_t gpt_devt =
	disk_devt(dev_to_disk(&root_bdev->bd_disk->part0->bd_device));
	dev_t kernel_devt =
	get_boot_dev() ?: get_boot_dev_from_root_dev(root_bdev);
	struct block_device *kernel_bdev;
	u8 kernel_gpt_entry_id;

	if (!gpt_devt)
	return -EINVAL;

	/* Get block device to get the partno. */
	kernel_bdev = blkdev_get_by_dev(kernel_devt, FMODE_READ,
	chromeos_update_tries, NULL);
	if (IS_ERR(kernel_bdev))
	return PTR_ERR(kernel_bdev);
	/*
	* GPT entry offset is 0 based, and partno, represented by MINOR,
	* is 1 based, so subtract 1.
	*/
	kernel_gpt_entry_id = kernel_bdev->bd_partno - 1;
	blkdev_put(kernel_bdev, chromeos_update_tries);

	bio = bio_alloc(root_bdev, 1, 0, GFP_NOIO);
	if (!bio) {
	ret = -1;
	goto failed_bio_alloc;
	}

	hdr_page = alloc_page(GFP_NOIO);
	tbl_pages = alloc_pages(GFP_NOIO, GPT_TABLE_PAGE_NUM_ORDER);
	if (!hdr_page \|\| !tbl_pages) {
	ret = -ENOMEM;
	goto failed;
	}

	header = page_address(hdr_page);

	if (chromeos_handle_retries(bio, gpt_devt, kernel_gpt_entry_id, 1,
	hdr_page, tbl_pages) \|\|
	chromeos_handle_retries(bio, gpt_devt, kernel_gpt_entry_id,
	le64_to_cpu(header->alternate_lba),
	hdr_page, tbl_pages)) {
	DMERR("update_tries: retry failed, will invalidated kernel");
	ret = -1;
	goto failed;
	}

	DMERR("update_tries: completed");
	ret = 0;
	failed:
	if (hdr_page)
	__free_page(hdr_page);
	if (tbl_pages)
	__free_pages(tbl_pages, GPT_TABLE_PAGE_NUM_ORDER);
	bio_put(bio);
	failed_bio_alloc:
	return ret;
	}

	static int error_handler(struct notifier_block *nb, unsigned long transient,
	void *opaque_err)
	{
	struct dm_verity_error_state *err =
	(struct dm_verity_error_state *) opaque_err;
	err->behavior = DM_VERITY_ERROR_BEHAVIOR_PANIC;
	if (transient)
	return 0;

	// Do not invalidate kernel if successfully updated try count.
	if (!chromeos_update_tries(err->dev))
	return 0;

	/* Mark the kernel partition as invalid. */
	chromeos_invalidate_kernel_bio(err->dev);
	return 0;
	}

	static struct notifier_block chromeos_nb = {
	.notifier_call = &error_handler,
	.next = NULL,
	.priority = 1,
	};

	static int __init dm_verity_chromeos_init(void)
	{
	int r;

	r = dm_verity_register_error_notifier(&chromeos_nb);
	if (r < 0)
	DMERR("failed to register handler: %d", r);
	else
	DMINFO("dm-verity-chromeos registered");
	return r;
	}

	static void __exit dm_verity_chromeos_exit(void)
	{
	dm_verity_unregister_error_notifier(&chromeos_nb);
	}

	module_init(dm_verity_chromeos_init);
	module_exit(dm_verity_chromeos_exit);

	MODULE_AUTHOR("Will Drewry <[email protected]>");
	MODULE_DESCRIPTION("chromeos-specific error handler for dm-verity");
	MODULE_LICENSE("GPL");

	/* Declare parameter with no module prefix */
	#undef MODULE_PARAM_PREFIX
	#define MODULE_PARAM_PREFIX ""
	module_param_string(kern_guid, kern_guid, sizeof(kern_guid), 0);