tpm2-tools源码分析之tpm2_changeauth.c（1）

TPM 2.0中的tpm2_changeauth命令对应的源文件就是tpm2_changeauth.c，该文件位于tpm2-tools/tools/下，一共有423行（版本5.5）。

tpm2_changeauth的功能是更改TPM对象的授权值。为各种层级、NV索引、临时对象和持久性对象配置授权值。

下边用几篇文章的篇幅对tpm2_changeauth.c文件结合tpm2_changeauth命令进行深入的、完全的解析。

先来看第一段代码：

// Register this tool with tpm2_tool.c
TPM2_TOOL_REGISTER("changeauth", tpm2_tool_onstart, tpm2_tool_onrun,
tpm2_tool_onstop, NULL)

TPM2_TOOL_REGISTER是一个宏定义，在tpm2-tools/tools/tpm2_tool.h中，代码如下：

#define TPM2_TOOL_REGISTER(tool_name,tool_onstart,tool_onrun,tool_onstop,tool_onexit) \
	static const tpm2_tool tool = { \
		.name		= tool_name, \
		.onstart	= tool_onstart, \
		.onrun		= tool_onrun, \
		.onstop		= tool_onstop, \
		.onexit		= tool_onexit, \
	}; \
	static void \
	__attribute__((__constructor__)) \
	__attribute__((__used__)) \
	_tpm2_tool_init(void) \
	{ \
		tpm2_tool_register(&tool); \
	}

在本文件tpm2_changeauth.c也可以说tpm2_changeauth命令中，宏展开后为：

static const tpm2_tool tool = {
    .name		= "changeauth",
	.onstart	= tpm2_tool_onstart,
	.onrun		= tpm2_tool_onrun,
	.onstop		= tpm2_tool_onstop,
	.onexit		= NULL,
};
static void
	__attribute__((__constructor__))
	__attribute__((__used__))
    _tpm2_tool_init(void)
{
		tpm2_tool_register(&tool);
}

tpm2_tool结构的定义也在tpm2-tools/tools/tpm2_tool.h中，代码如下：

typedef struct {
	const char * name;
	tpm2_tool_onstart_t onstart;
	tpm2_tool_onrun_t onrun;
	tpm2_tool_onstop_t onstop;
	tpm2_tool_onexit_t onexit;
} tpm2_tool;

其中包含的相关函数指针如下（同文件中，就在上边）：

/**
 * An optional interface for tools to specify what options they support.
 * They are concatenated with main's options and passed to getopt_long.
 * @param opts
 *  The callee can choose to set *opts to a tpm_options pointer allocated
 *  via tpm2_options_new(). Setting *opts to NULL is not an error, and
 *  Indicates that no options are specified by the tool.
 *
 * @return
 *  True on success, false on error.
 */
typedef bool (*tpm2_tool_onstart_t)(tpm2_options **opts);
 
/**
 * This is the main interface for tools, after tcti and sapi/esapi initialization
 * are performed.
 * @param ectx
 *  The system/esapi api context.
 * @param flags
 *  Flags that tools may wish to respect.
 * @return
 *  A tool_rc indicating status.
 */
typedef tool_rc (*tpm2_tool_onrun_t)(ESYS_CONTEXT *ectx, tpm2_option_flags flags);
 
/**
 * Called after tpm2_tool_onrun() is invoked. ESAPI context is still valid during this call.
 * @param ectx
 *  The system/esapi api context.
 * @return
 *  A tool_rc indicating status.
 */
typedef tool_rc (*tpm2_tool_onstop_t)(ESYS_CONTEXT *ectx);
 
/**
 * Called when the tool is exiting, useful for cleanup.
 */
typedef void (*tpm2_tool_onexit_t)(void);

tpm2_tool_register函数在tpm2-tools/tools/tpm2_tools.c中实现，代码如下：

/*
 * Build a list of the TPM2 tools linked into this executable
 */
#ifndef TPM2_TOOLS_MAX
#define TPM2_TOOLS_MAX 1024
#endif
static const tpm2_tool *tools[TPM2_TOOLS_MAX];
static unsigned tool_count;
 
void tpm2_tool_register(const tpm2_tool *tool) {
 
    if (tool_count < TPM2_TOOLS_MAX) {
        tools[tool_count++] = tool;
    } else {
        LOG_ERR("Over tool count");
        abort();
    }
}

回到tpm2_changeauth.c中，来看具体的几个函数。

（1）tpm2_tool_onstart

tpm2_tool_onstart函数代码如下：

static bool tpm2_tool_onstart(tpm2_options **opts) {

    struct option topts[] = {
        { "object-auth",    required_argument, NULL, 'p' },
        { "object-context", required_argument, NULL, 'c' },
        { "parent-context", required_argument, NULL, 'C' },
        { "private",        required_argument, NULL, 'r' },
        { "cphash",         required_argument, NULL,  0  },
        { "rphash",         required_argument, NULL,  1  },
        { "session",        required_argument, NULL, 'S' },
    };
    *opts = tpm2_options_new("p:c:C:r:S:", ARRAY_LEN(topts), topts,
                             on_option, on_arg, 0);

    return *opts != NULL;
}

（2）tpm2_tool_onrun

tpm2_tool_onrun函数代码如下：

static tool_rc tpm2_tool_onrun(ESYS_CONTEXT *ectx, tpm2_option_flags flags) {

    UNUSED(flags);

    /*
     * 1. Process options
     */
    tool_rc rc = check_options();
    if (rc != tool_rc_success) {
        return rc;
    }

    /*
     * 2. Process inputs
     */
    rc = process_inputs(ectx);
    if (rc != tool_rc_success) {
        return rc;
    }

    /*
     * 3. TPM2_CC_<command> call
     */
    rc = change_authorization(ectx);
    if (rc != tool_rc_success) {
        return rc;
    }

    /*
     * 4. Process outputs
     */
    return process_output(ectx);
}

（3）tpm2_tool_onstop

tpm2_tool_onstop函数代码如下：

static tool_rc tpm2_tool_onstop(ESYS_CONTEXT *ectx) {

    UNUSED(ectx);

    /*
     * 1. Free objects
     */

    /*
     * 2. Close authorization sessions
     */
    tool_rc rc = tool_rc_success;
    tool_rc tmp_rc = tpm2_session_close(&ctx.object.new);
    if (tmp_rc != tool_rc_success) {
        rc = tmp_rc;
    }

    tmp_rc = tpm2_session_close(&ctx.object.obj.session);
    if (tmp_rc != tool_rc_success) {
        rc = tmp_rc;
    }

    tmp_rc = tpm2_session_close(&ctx.parent.obj.session);
    if (tmp_rc != tool_rc_success) {
        rc = tmp_rc;
    }

    /*
     * 3. Close auxiliary sessions
     */
    size_t i = 0;
    for(i = 0; i < ctx.aux_session_cnt; i++) {
        if (ctx.aux_session_path[i]) {
            tmp_rc = tpm2_session_close(&ctx.aux_session[i]);
            if (tmp_rc != tool_rc_success) {
                rc = tmp_rc;
            }
        }
    }

    return rc;
}

后续文章对这几个函数进行深入解析。