firmware/2lib/include/2api.h

/* Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

/* APIs between calling firmware and vboot_reference
 *
 * General notes:
 *
 * TODO: split this file into a vboot_entry_points.h file which contains the
 * entry points for the firmware to call vboot_reference, and a
 * vboot_firmware_exports.h which contains the APIs to be implemented by the
 * calling firmware and exported to vboot_reference.
 *
 * Notes:
 *    * Assumes this code is never called in the S3 resume path.  TPM resume
 *      must be done elsewhere, and VB2_NV_DEBUG_RESET_MODE is ignored.
 */

#ifndef VBOOT_2_API_H_
#define VBOOT_2_API_H_
#include <stdint.h>

#include "2common.h"
#include "2constants.h"
#include "2crypto.h"
#include "2fw_hash_tags.h"
#include "2id.h"
#include "2recovery_reasons.h"
#include "2return_codes.h"

/* Modes for vb2ex_tpm_set_mode. */
enum vb2_tpm_mode {
	/*
	 * TPM is enabled tentatively, and may be set to either
	 * ENABLED or DISABLED mode.
	 */
	VB2_TPM_MODE_ENABLED_TENTATIVE = 0,

	/* TPM is enabled, and mode may not be changed. */
	VB2_TPM_MODE_ENABLED = 1,

	/* TPM is disabled, and mode may not be changed. */
	VB2_TPM_MODE_DISABLED = 2,
};

/* Flags for vb2_context.
 *
 * Unless otherwise noted, flags are set by verified boot and may be read (but
 * not set or cleared) by the caller.
 */
enum vb2_context_flags {

	/*
	 * Verified boot has changed nvdata[].  Caller must save nvdata[] back
	 * to its underlying storage, then may clear this flag.
	 */
	VB2_CONTEXT_NVDATA_CHANGED = (1 << 0),

	/*
	 * Verified boot has changed secdata[].  Caller must save secdata[]
	 * back to its underlying storage, then may clear this flag.
	 */
	VB2_CONTEXT_SECDATA_CHANGED = (1 << 1),

	/* Recovery mode is requested this boot */
	VB2_CONTEXT_RECOVERY_MODE = (1 << 2),

	/* Developer mode is requested this boot */
	VB2_CONTEXT_DEVELOPER_MODE = (1 << 3),

	/*
	 * Force recovery mode due to physical user request.  Caller may set
	 * this flag when initializing the context.
	 */
	VB2_CONTEXT_FORCE_RECOVERY_MODE = (1 << 4),

	/*
	 * Force developer mode enabled.  Caller may set this flag when
	 * initializing the context.
	 *
	 * Deprecated as part of chromium:942901.
	 */
	VB2_CONTEXT_FORCE_DEVELOPER_MODE = (1 << 5),

	/* Using firmware slot B.  If this flag is clear, using slot A. */
	VB2_CONTEXT_FW_SLOT_B = (1 << 6),

	/* RAM should be cleared by caller this boot */
	VB2_CONTEXT_CLEAR_RAM = (1 << 7),

	/* Wipeout by the app should be requested. */
	VB2_CONTEXT_FORCE_WIPEOUT_MODE = (1 << 8),

	/* Erase TPM developer mode state if it is enabled. */
	VB2_CONTEXT_DISABLE_DEVELOPER_MODE = (1 << 9),

	/*
	 * Verified boot has changed secdatak[].  Caller must save secdatak[]
	 * back to its underlying storage, then may clear this flag.
	 */
	VB2_CONTEXT_SECDATAK_CHANGED = (1 << 10),

	/*
	 * Allow kernel verification to roll forward the version in secdatak[].
	 * Caller may set this flag before calling vb2api_kernel_phase3().
	 */
	VB2_CONTEXT_ALLOW_KERNEL_ROLL_FORWARD = (1 << 11),

	/*
	 * Boot optimistically: don't touch failure counters.  Caller may set
	 * this flag when initializing the context.
	 */
	VB2_CONTEXT_NOFAIL_BOOT = (1 << 12),

	/*
	 * Secdata is not ready this boot, but should be ready next boot.  It
	 * would like to reboot.  The decision whether to reboot or not must be
	 * deferred until vboot, because rebooting all the time before then
	 * could cause a device with malfunctioning secdata to get stuck in an
	 * unrecoverable crash loop.
	 */
	VB2_CONTEXT_SECDATA_WANTS_REBOOT = (1 << 13),

	/*
	 * Boot is S3->S0 resume, not S5->S0 normal boot.  Caller may set this
	 * flag when initializing the context.
	 */
	VB2_CONTEXT_S3_RESUME = (1 << 14),

	/*
	 * System supports EC software sync.  Caller may set this flag at any
	 * time before calling VbSelectAndLoadKernel().
	 */
	VB2_CONTEXT_EC_SYNC_SUPPORTED = (1 << 15),

	/*
	 * EC software sync is slow to update; warning screen should be
	 * displayed.  Caller may set this flag at any time before calling
	 * VbSelectAndLoadKernel().
	 */
	VB2_CONTEXT_EC_SYNC_SLOW = (1 << 16),

	/*
	 * EC firmware supports early firmware selection; two EC images exist,
	 * and EC may have already verified and jumped to EC-RW prior to EC
	 * software sync.
	 */
	VB2_CONTEXT_EC_EFS = (1 << 17),

	/*
	 * NV storage uses data format V2.  Data is size VB2_NVDATA_SIZE_V2,
	 * not VB2_NVDATA_SIZE.
	 *
	 * Caller must set this flag when initializing the context to use V2.
	 * (Vboot cannot infer the data size from the data itself, because the
	 * data provided by the caller could be uninitialized.)
	 */
	VB2_CONTEXT_NVDATA_V2 = (1 << 18),

	/* Allow vendor data to be set via the vendor data ui. */
	VB2_CONTEXT_VENDOR_DATA_SETTABLE = (1 << 19),
};

/*
 * Context for firmware verification.  Pass this to all vboot APIs.
 *
 * Caller may relocate this between calls to vboot APIs.
 */
struct vb2_context {
	/**********************************************************************
	 * Fields which must be initialized by caller.
	 */

	/*
	 * Flags; see vb2_context_flags.  Some flags may only be set by caller
	 * prior to calling vboot functions.
	 */
	uint32_t flags;

	/*
	 * Work buffer, and length in bytes.  Caller may relocate this between
	 * calls to vboot APIs; it contains no internal pointers.  Caller must
	 * not examine the contents of this work buffer directly.
	 */
	uint8_t *workbuf;
	uint32_t workbuf_size;

	/*
	 * Non-volatile data.  Caller must fill this from some non-volatile
	 * location.  If the VB2_CONTEXT_NVDATA_CHANGED flag is set when a
	 * vb2api function returns, caller must save the data back to the
	 * non-volatile location and then clear the flag.
	 */
	uint8_t nvdata[VB2_NVDATA_SIZE_V2];

	/*
	 * Secure data for firmware verification stage.  Caller must fill this
	 * from some secure non-volatile location.  If the
	 * VB2_CONTEXT_SECDATA_CHANGED flag is set when a function returns,
	 * caller must save the data back to the secure non-volatile location
	 * and then clear the flag.
	 */
	uint8_t secdata[VB2_SECDATA_SIZE];

	/*
	 * Context pointer for use by caller.  Verified boot never looks at
	 * this.  Put context here if you need it for APIs that verified boot
	 * may call (vb2ex_...() functions).
	 */
	void *non_vboot_context;

	/**********************************************************************
	 * Fields caller may examine after calling vb2api_fw_phase1().  Caller
	 * must set these fields to 0 before calling any vboot functions.
	 */

	/*
	 * Amount of work buffer used so far.  Verified boot sub-calls use
	 * this to know where the unused work area starts.  Caller may use
	 * this between calls to vboot APIs to know how much data must be
	 * copied when relocating the work buffer.
	 */
	uint32_t workbuf_used;

	/**********************************************************************
	 * Fields caller must initialize before calling vb2api_kernel_phase1().
	 */

	/*
	 * Secure data for kernel verification stage.  Caller must fill this
	 * from some secure non-volatile location.  If the
	 * VB2_CONTEXT_SECDATAK_CHANGED flag is set when a function returns,
	 * caller must save the data back to the secure non-volatile location
	 * and then clear the flag.
	 */
	uint8_t secdatak[VB2_SECDATAK_SIZE];
};

/* Resource index for vb2ex_read_resource() */
enum vb2_resource_index {

	/* Google binary block */
	VB2_RES_GBB,

	/*
	 * Firmware verified boot block (keyblock+preamble).  Use
	 * VB2_CONTEXT_FW_SLOT_B to determine whether this refers to slot A or
	 * slot B; vboot will set that flag to the proper state before reading
	 * the vblock.
	 */
	VB2_RES_FW_VBLOCK,

	/*
	 * Kernel verified boot block (keyblock+preamble) for the current
	 * kernel partition.  Used only by vb2api_kernel_load_vblock().
	 * Contents are allowed to change between calls to that function (to
	 * allow multiple kernels to be examined).
	 */
	VB2_RES_KERNEL_VBLOCK,
};

/* Digest ID for vbapi_get_pcr_digest() */
enum vb2_pcr_digest {
	/* Digest based on current developer and recovery mode flags */
	BOOT_MODE_PCR,

	/* SHA-256 hash digest of HWID, from GBB */
	HWID_DIGEST_PCR,
};

/******************************************************************************
 * APIs provided by verified boot.
 *
 * At a high level, call functions in the order described below.  After each
 * call, examine vb2_context.flags to determine whether nvdata or secdata
 * needs to be written.
 *
 * If you need to cause the boot process to fail at any point, call
 * vb2api_fail().  Then check vb2_context.flags to see what data needs to be
 * written.  Then reboot.
 *
 *	Load nvdata from wherever you keep it.
 *
 *	Load secdata from wherever you keep it.
 *
 *      	If it wasn't there at all (for example, this is the first boot
 *		of a new system in the factory), call vb2api_secdata_create()
 *		to initialize the data.
 *
 *		If access to your storage is unreliable (reads/writes may
 *		contain corrupt data), you may call vb2api_secdata_check() to
 *		determine if the data was valid, and retry reading if it
 *		wasn't.  (In that case, you should also read back and check the
 *		data after any time you write it, to make sure it was written
 *		correctly.)
 *
 *	Call vb2api_fw_phase1().  At present, this nominally decides whether
 *	recovery mode is needed this boot.
 *
 *	Call vb2api_fw_phase2().  At present, this nominally decides which
 *	firmware slot will be attempted (A or B).
 *
 *	Call vb2api_fw_phase3().  At present, this nominally verifies the
 *	firmware keyblock and preamble.
 *
 *	Lock down wherever you keep secdata.  It should no longer be writable
 *	this boot.
 *
 *	Verify the hash of each section of code/data you need to boot the RW
 *	firmware.  For each section:
 *
 *		Call vb2_init_hash() to see if the hash exists.
 *
 *		Load the data for the section.  Call vb2_extend_hash() on the
 *		data as you load it.  You can load it all at once and make one
 *		call, or load and hash-extend a block at a time.
 *
 *		Call vb2_check_hash() to see if the hash is valid.
 *
 *			If it is valid, you may use the data and/or execute
 *			code from that section.
 *
 *			If the hash was invalid, you must reboot.
 *
 * At this point, firmware verification is done, and vb2_context contains the
 * kernel key needed to verify the kernel.  That context should be preserved
 * and passed on to kernel selection.  The kernel selection process may be
 * done by the same firmware image, or may be done by the RW firmware.  The
 * recommended order is:
 *
 *	Load secdatak from wherever you keep it.
 *
 *      	If it wasn't there at all (for example, this is the first boot
 *		of a new system in the factory), call vb2api_secdatak_create()
 *		to initialize the data.
 *
 *		If access to your storage is unreliable (reads/writes may
 *		contain corrupt data), you may call vb2api_secdatak_check() to
 *		determine if the data was valid, and retry reading if it
 *		wasn't.  (In that case, you should also read back and check the
 *		data after any time you write it, to make sure it was written
 *		correctly.)
 *
 *	Call vb2api_kernel_phase1().  At present, this decides which key to
 *	use to verify kernel data - the recovery key from the GBB, or the
 *	kernel subkey from the firmware verification stage.
 *
 *	Kernel phase 2 is finding loading, and verifying the kernel partition.
 *
 *	Find a boot device (you're on your own here).
 *
 *	Call vb2api_load_kernel_vblock() for each kernel partition on the
 *	boot device, until one succeeds.
 *
 *	When that succeeds, call vb2api_get_kernel_size() to determine where
 *	the kernel is located in the stream and how big it is.  Load or map
 *	the kernel.  (Again, you're on your own.  This is the responsibility of
 *	the caller so that the caller can choose whether to allocate a buffer,
 *	load the kernel data into a predefined area of RAM, or directly map a
 *	kernel file into the address space.  Note that technically it doesn't
 *	matter whether the kernel data is even in the same file or stream as
 *	the vblock, as long as the caller loads the right data.
 *
 *	Call vb2api_verify_kernel_data() on the kernel data.
 *
 *	If you ran out of kernels before finding a good one, call vb2api_fail()
 *	with an appropriate recovery reason.
 *
 *	Set the VB2_CONTEXT_ALLOW_KERNEL_ROLL_FORWARD flag if the current
 *	kernel partition has the successful flag (that is, it's already known
 *	or assumed to be a functional kernel partition).
 *
 *	Call vb2api_kernel_phase3().  This cleans up from kernel verification
 *	and updates the secure data if needed.
 *
 *	Lock down wherever you keep secdatak.  It should no longer be writable
 *	this boot.
 */

/**
 * Sanity-check the contents of the secure storage context.
 *
 * Use this if reading from secure storage may be flaky, and you want to retry
 * reading it several times.
 *
 * This may be called before vb2api_phase1().
 *
 * @param ctx		Context pointer
 * @return VB2_SUCCESS, or non-zero error code if error.
 */
int vb2api_secdata_check(const struct vb2_context *ctx);

/**
 * Create fresh data in the secure storage context.
 *
 * Use this only when initializing the secure storage context on a new machine
 * the first time it boots.  Do NOT simply use this if vb2api_secdata_check()
 * (or any other API in this library) fails; that could allow the secure data
 * to be rolled back to an insecure state.
 *
 * This may be called before vb2api_phase1().
 *
 * @param ctx		Context pointer
 * @return VB2_SUCCESS, or non-zero error code if error.
 */
int vb2api_secdata_create(struct vb2_context *ctx);

/**
 * Sanity-check the contents of the kernel version secure storage context.
 *
 * Use this if reading from secure storage may be flaky, and you want to retry
 * reading it several times.
 *
 * This may be called before vb2api_phase1().
 *
 * @param ctx		Context pointer
 * @return VB2_SUCCESS, or non-zero error code if error.
 */
int vb2api_secdatak_check(const struct vb2_context *ctx);

/**
 * Create fresh data in the kernel version secure storage context.
 *
 * Use this only when initializing the secure storage context on a new machine
 * the first time it boots.  Do NOT simply use this if vb2api_secdatak_check()
 * (or any other API in this library) fails; that could allow the secure data
 * to be rolled back to an insecure state.
 *
 * This may be called before vb2api_phase1().
 *
 * @param ctx		Context pointer
 * @return VB2_SUCCESS, or non-zero error code if error.
 */
int vb2api_secdatak_create(struct vb2_context *ctx);

/**
 * Report firmware failure to vboot.
 *
 * This may be called before vb2api_phase1() to indicate errors in the boot
 * process prior to the start of vboot.
 *
 * If this is called after vb2api_phase1(), on return, the calling firmware
 * should check for updates to secdata and/or nvdata, then reboot.
 *
 * @param reason	Recovery reason
 * @param subcode	Recovery subcode
 */
void vb2api_fail(struct vb2_context *ctx, uint8_t reason, uint8_t subcode);

/**
 * Firmware selection, phase 1.
 *
 * If the returned error is VB2_ERROR_API_PHASE1_RECOVERY, the calling firmware
 * should jump directly to recovery-mode firmware without rebooting.
 *
 * For other errors, the calling firmware should check for updates to secdata
 * and/or nvdata, then reboot.
 *
 * @param ctx		Vboot context
 * @return VB2_SUCCESS, or error code on error.
 */
int vb2api_fw_phase1(struct vb2_context *ctx);

/**
 * Firmware selection, phase 2.
 *
 * On error, the calling firmware should check for updates to secdata and/or
 * nvdata, then reboot.
 *
 * @param ctx		Vboot context
 * @return VB2_SUCCESS, or error code on error.
 */
int vb2api_fw_phase2(struct vb2_context *ctx);

/**
 * Firmware selection, phase 3.
 *
 * On error, the calling firmware should check for updates to secdata and/or
 * nvdata, then reboot.
 *
 * On success, the calling firmware should lock down secdata before continuing
 * with the boot process.
 *
 * @param ctx		Vboot context
 * @return VB2_SUCCESS, or error code on error.
 */
int vb2api_fw_phase3(struct vb2_context *ctx);

/**
 * Same, but for new-style structs.
 */
int vb21api_fw_phase3(struct vb2_context *ctx);

/**
 * Initialize hashing data for the specified tag.
 *
 * @param ctx		Vboot context
 * @param tag		Tag to start hashing (enum vb2_hash_tag)
 * @param size		If non-null, expected size of data for tag will be
 *			stored here on output.
 * @return VB2_SUCCESS, or error code on error.
 */
int vb2api_init_hash(struct vb2_context *ctx, uint32_t tag, uint32_t *size);

/**
 * Same, but for new-style structs.
 */
int vb21api_init_hash(struct vb2_context *ctx,
		      const struct vb2_id *id,
		      uint32_t *size);

/**
 * Extend the hash started by vb2api_init_hash() with additional data.
 *
 * (This is the same for both old and new style structs.)
 *
 * @param ctx		Vboot context
 * @param buf		Data to hash
 * @param size		Size of data in bytes
 * @return VB2_SUCCESS, or error code on error.
 */
int vb2api_extend_hash(struct vb2_context *ctx,
		       const void *buf,
		       uint32_t size);

/**
 * Check the hash value started by vb2api_init_hash().
 *
 * @param ctx		Vboot context
 * @return VB2_SUCCESS, or error code on error.
 */
int vb2api_check_hash(struct vb2_context *ctx);

/**
 * Same, but for new-style structs.
 */
int vb21api_check_hash(struct vb2_context *ctx);

/**
 * Check the hash value started by vb2api_init_hash() while retrieving
 * calculated digest.
 *
 * @param ctx			Vboot context
 * @param digest_out		optional pointer to buffer to store digest
 * @param digest_out_size	optional size of buffer to store digest
 * @return VB2_SUCCESS, or error code on error.
 */
int vb2api_check_hash_get_digest(struct vb2_context *ctx, void *digest_out,
				 uint32_t digest_out_size);

/**
 * Get a PCR digest
 *
 * @param ctx		Vboot context
 * @param which_digest	PCR index of the digest
 * @param dest		Destination where the digest is copied.
 * 			Recommended size is VB2_PCR_DIGEST_RECOMMENDED_SIZE.
 * @param dest_size	IN: size of the buffer pointed by dest
 * 			OUT: size of the copied digest
 * @return VB2_SUCCESS, or error code on error
 */
int vb2api_get_pcr_digest(struct vb2_context *ctx,
			  enum vb2_pcr_digest which_digest,
			  uint8_t *dest,
			  uint32_t *dest_size);

/**
 * Prepare for kernel verification stage.
 *
 * Must be called before other vb2api kernel functions.
 *
 * @param ctx		Vboot context
 * @return VB2_SUCCESS, or error code on error.
 */
int vb2api_kernel_phase1(struct vb2_context *ctx);

/**
 * Load the verified boot block (vblock) for a kernel.
 *
 * This function may be called multiple times, to load and verify the
 * vblocks from multiple kernel partitions.
 *
 * @param ctx		Vboot context
 * @param stream	Kernel stream
 * @return VB2_SUCCESS, or error code on error.
 */
int vb2api_load_kernel_vblock(struct vb2_context *ctx);

/**
 * Get the size and offset of the kernel data for the most recent vblock.
 *
 * Valid after a successful call to vb2api_load_kernel_vblock().
 *
 * @param ctx		Vboot context
 * @param offset_ptr	Destination for offset in bytes of kernel data as
 *			reported by vblock.
 * @param size_ptr      Destination for size of kernel data in bytes.
 * @return VB2_SUCCESS, or error code on error.
 */
int vb2api_get_kernel_size(struct vb2_context *ctx,
			   uint32_t *offset_ptr,
			   uint32_t *size_ptr);

/**
 * Verify kernel data using the previously loaded kernel vblock.
 *
 * Valid after a successful call to vb2api_load_kernel_vblock().  This allows
 * the caller to load or map the kernel data, as appropriate, and pass the
 * pointer to the kernel data into vboot.
 *
 * @param ctx		Vboot context
 * @param buf		Pointer to kernel data
 * @param size		Size of kernel data in bytes
 * @return VB2_SUCCESS, or error code on error.
 */
int vb2api_verify_kernel_data(struct vb2_context *ctx,
			      const void *buf,
			      uint32_t size);

/**
 * Clean up after kernel verification.
 *
 * Call this after successfully loading a vblock and verifying kernel data,
 * or if you've run out of boot devices and/or kernel partitions.
 *
 * This cleans up intermediate data structures in the vboot context, and
 * updates the version in the secure data if necessary.
 */
int vb2api_kernel_phase3(struct vb2_context *ctx);

/*****************************************************************************/
/* APIs provided by the caller to verified boot */

/**
 * Clear the TPM owner.
 *
 * @param ctx		Vboot context
 * @return VB2_SUCCESS, or error code on error.
 */
int vb2ex_tpm_clear_owner(struct vb2_context *ctx);

/**
 * Read a verified boot resource.
 *
 * @param ctx		Vboot context
 * @param index		Resource index to read
 * @param offset	Byte offset within resource to start at
 * @param buf		Destination for data
 * @param size		Amount of data to read
 * @return VB2_SUCCESS, or error code on error.
 */
int vb2ex_read_resource(struct vb2_context *ctx,
			enum vb2_resource_index index,
			uint32_t offset,
			void *buf,
			uint32_t size);

/**
 * Print debug output
 *
 * This should work like printf().  If func!=NULL, it will be a string with
 * the current function name; that can be used to generate prettier debug
 * output.  If func==NULL, don't print any extra header/trailer so that this
 * can be used to composite a bigger output string from several calls - for
 * example, when doing a hex dump.
 *
 * @param func		Function name generating output, or NULL.
 * @param fmt		Printf format string
 */
void vb2ex_printf(const char *func, const char *fmt, ...);

/**
 * Initialize the hardware crypto engine to calculate a block-style digest.
 *
 * @param hash_alg	Hash algorithm to use
 * @param data_size	Expected total size of data to hash
 * @return VB2_SUCCESS, or non-zero error code (HWCRYPTO_UNSUPPORTED not fatal).
 */
int vb2ex_hwcrypto_digest_init(enum vb2_hash_algorithm hash_alg,
			       uint32_t data_size);

/**
 * Extend the hash in the hardware crypto engine with another block of data.
 *
 * @param buf		Next data block to hash
 * @param size		Length of data block in bytes
 * @return VB2_SUCCESS, or non-zero error code.
 */
int vb2ex_hwcrypto_digest_extend(const uint8_t *buf, uint32_t size);

/**
 * Finalize the digest in the hardware crypto engine and extract the result.
 *
 * @param digest	Destination buffer for resulting digest
 * @param digest_size	Length of digest buffer in bytes
 * @return VB2_SUCCESS, or non-zero error code.
 */
int vb2ex_hwcrypto_digest_finalize(uint8_t *digest, uint32_t digest_size);

/**
 * Calculate the digest of a buffer and store the result.
 *
 * @param buf		Data to hash
 * @param size		Length of data in bytes
 * @param hash_alg	Hash algorithm
 * @param digest	Destination for digest
 * @param digest_size	Length of digest buffer in bytes.
 * @return VB2_SUCCESS, or non-zero on error.
 */
int vb2api_digest_buffer(const uint8_t *buf,
			 uint32_t size,
			 enum vb2_hash_algorithm hash_alg,
			 uint8_t *digest,
			 uint32_t digest_size);

/*
 * Set the current TPM mode value, and validate that it was changed.  If one
 * of the following occurs, the function call fails:
 *   - TPM does not understand the instruction (old version)
 *   - TPM has already left the TpmModeEnabledTentative mode
 *   - TPM responds with a mode other than the requested mode
 *   - Some other communication error occurs
 *  Otherwise, the function call succeeds.
 *
 * @param mode_val       Desired TPM mode to set.  May be one of ENABLED
 *                       or DISABLED from vb2_tpm_mode enum.
 * @returns VB2_SUCCESS, or non-zero error code.
 */
int vb2ex_tpm_set_mode(enum vb2_tpm_mode mode_val);

#endif  /* VBOOT_2_API_H_ */