platform_util.h File Reference

Common and shared functions used by multiple modules in the Mbed TLS library. More...

#include "mbedtls/config.h"
#include <stddef.h>
#include "mbedtls/platform_time.h"
#include <time.h>

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Macros
#define	MBEDTLS_INTERNAL_VALIDATE_RET(cond, ret)   do { } while (0)
#define	MBEDTLS_INTERNAL_VALIDATE(cond)   do { } while (0)
#define	MBEDTLS_DEPRECATED_STRING_CONSTANT(VAL)   VAL
#define	MBEDTLS_DEPRECATED_NUMERIC_CONSTANT(VAL)   VAL
#define	MBEDTLS_CHECK_RETURN_CRITICAL   MBEDTLS_CHECK_RETURN
#define	MBEDTLS_CHECK_RETURN_TYPICAL
#define	MBEDTLS_CHECK_RETURN_OPTIONAL
SECTION: Module configuration options
This section allows for the setting of module specific sizes and configuration options. The default values are already present in the relevant header files and should suffice for the regular use cases. Our advice is to enable options and change their values here only if you have a good reason and know the consequences.
#define	MBEDTLS_CHECK_RETURN
	This macro is invoked by the library when an invalid parameter is detected that is only checked with #MBEDTLS_CHECK_PARAMS (see the documentation of that option for context).
#define	MBEDTLS_IGNORE_RETURN(result)   ((void) !(result))

Functions
void	mbedtls_platform_zeroize (void *buf, size_t len)
	Securely zeroize a buffer.
struct tm *	mbedtls_platform_gmtime_r (const mbedtls_time_t *tt, struct tm *tm_buf)
	Platform-specific implementation of gmtime_r()

Detailed Description

Common and shared functions used by multiple modules in the Mbed TLS library.

Definition in file platform_util.h.

Macro Definition Documentation

MBEDTLS_CHECK_RETURN

#define MBEDTLS_CHECK_RETURN

This macro is invoked by the library when an invalid parameter is detected that is only checked with #MBEDTLS_CHECK_PARAMS (see the documentation of that option for context).

When you leave this undefined here, the library provides a default definition. If the macro #MBEDTLS_CHECK_PARAMS_ASSERT is defined, the default definition is assert(cond), otherwise the default definition calls a function mbedtls_param_failed(). This function is declared in platform_util.h for the benefit of the library, but you need to define in your application.

When you define this here, this replaces the default definition in platform_util.h (which no longer declares the function mbedtls_param_failed()) and it is your responsibility to make sure this macro expands to something suitable (in particular, that all the necessary declarations are visible from within the library - you can ensure that by providing them in this file next to the macro definition). If you define this macro to call assert, also define #MBEDTLS_CHECK_PARAMS_ASSERT so that library source files include <assert.h>.

Note that you may define this macro to expand to nothing, in which case you don't have to worry about declarations or definitions. However, you will then be notified about invalid parameters only in non-void functions, and void function will just silently return early on invalid parameters, which partially negates the benefits of enabling #MBEDTLS_CHECK_PARAMS in the first place, so is discouraged.

Parameters

cond	The expression that should evaluate to true, but doesn't.

This macro is used at the beginning of the declaration of a function to indicate that its return value should be checked. It should instruct the compiler to emit a warning or an error if the function is called without checking its return value.

There is a default implementation for popular compilers in platform_util.h. You can override the default implementation by defining your own here.

If the implementation here is empty, this will effectively disable the checking of functions' return values.

Definition at line 137 of file platform_util.h.

MBEDTLS_CHECK_RETURN_CRITICAL

#define MBEDTLS_CHECK_RETURN_CRITICAL   MBEDTLS_CHECK_RETURN

Critical-failure function

This macro appearing at the beginning of the declaration of a function indicates that its return value should be checked in all applications. Omitting the check is very likely to indicate a bug in the application and will result in a compile-time warning if MBEDTLS_CHECK_RETURN is implemented for the compiler in use.

Note

The use of this macro is a work in progress. This macro may be added to more functions in the future. Such an extension is not considered an API break, provided that there are near-unavoidable circumstances under which the function can fail. For example, signature/MAC/AEAD verification functions, and functions that require a random generator, are considered return-check-critical.

Definition at line 157 of file platform_util.h.

MBEDTLS_CHECK_RETURN_OPTIONAL

#define MBEDTLS_CHECK_RETURN_OPTIONAL

Benign-failure function

This macro appearing at the beginning of the declaration of a function indicates that it is rarely useful to check its return value.

This macro has an empty expansion. It exists for documentation purposes: a MBEDTLS_CHECK_RETURN_OPTIONAL annotation indicates that the function has been analyzed for return-check usefulness, whereas the lack of an annotation indicates that the function has not been analyzed and its return-check usefulness is unknown.

Definition at line 193 of file platform_util.h.

MBEDTLS_CHECK_RETURN_TYPICAL

#define MBEDTLS_CHECK_RETURN_TYPICAL

Ordinary-failure function

This macro appearing at the beginning of the declaration of a function indicates that its return value should be generally be checked in portable applications. Omitting the check will result in a compile-time warning if MBEDTLS_CHECK_RETURN is implemented for the compiler in use and #MBEDTLS_CHECK_RETURN_WARNING is enabled in the compile-time configuration.

You can use MBEDTLS_IGNORE_RETURN to explicitly ignore the return value of a function that is annotated with MBEDTLS_CHECK_RETURN.

Note

The use of this macro is a work in progress. This macro will be added to more functions in the future. Eventually this should appear before most functions returning an error code (as int in the mbedtls_xxx API or as psa_status_t in the psa_xxx API).

Definition at line 179 of file platform_util.h.

MBEDTLS_DEPRECATED_NUMERIC_CONSTANT

#define MBEDTLS_DEPRECATED_NUMERIC_CONSTANT

(

VAL

)

VAL

Definition at line 119 of file platform_util.h.

MBEDTLS_DEPRECATED_STRING_CONSTANT

#define MBEDTLS_DEPRECATED_STRING_CONSTANT

(

VAL

)

VAL

Definition at line 118 of file platform_util.h.

MBEDTLS_IGNORE_RETURN

#define MBEDTLS_IGNORE_RETURN

(

result

)

((void) !(result))

This macro requires one argument, which should be a C function call. If that function call would cause a MBEDTLS_CHECK_RETURN warning, this warning is suppressed.

Call this macro with one argument, a function call, to suppress a warning from MBEDTLS_CHECK_RETURN due to that function call.

Definition at line 209 of file platform_util.h.

MBEDTLS_INTERNAL_VALIDATE

#define MBEDTLS_INTERNAL_VALIDATE

(

cond

)

do { } while (0)

Definition at line 98 of file platform_util.h.

MBEDTLS_INTERNAL_VALIDATE_RET

#define MBEDTLS_INTERNAL_VALIDATE_RET	(		cond,
			ret
	)		do { } while (0)

Definition at line 97 of file platform_util.h.

Function Documentation

mbedtls_platform_gmtime_r()

struct tm * mbedtls_platform_gmtime_r	(	const mbedtls_time_t *	tt,
		struct tm *	tm_buf
	)

Platform-specific implementation of gmtime_r()

        The function is a thread-safe abstraction that behaves
        similarly to the gmtime_r() function from Unix/POSIX.

        Mbed TLS will try to identify the underlying platform and
        make use of an appropriate underlying implementation (e.g.
        gmtime_r() for POSIX and gmtime_s() for Windows). If this is
        not possible, then gmtime() will be used. In this case, calls
        from the library to gmtime() will be guarded by the mutex
        mbedtls_threading_gmtime_mutex if MBEDTLS_THREADING_C is
        enabled. It is recommended that calls from outside the library
        are also guarded by this mutex.

        If MBEDTLS_PLATFORM_GMTIME_R_ALT is defined, then Mbed TLS will
        unconditionally use the alternative implementation for
        mbedtls_platform_gmtime_r() supplied by the user at compile time.

Parameters

tt	Pointer to an object containing time (in seconds) since the epoch to be converted
tm_buf	Pointer to an object where the results will be stored

Returns

Pointer to an object of type struct tm on success, otherwise NULL

mbedtls_platform_zeroize()

void mbedtls_platform_zeroize	(	void *	buf,
		size_t	len
	)

Securely zeroize a buffer.

         The function is meant to wipe the data contained in a buffer so
         that it can no longer be recovered even if the program memory
         is later compromised. Call this function on sensitive data
         stored on the stack before returning from a function, and on
         sensitive data stored on the heap before freeing the heap
         object.

         It is extremely difficult to guarantee that calls to
         mbedtls_platform_zeroize() are not removed by aggressive
         compiler optimizations in a portable way. For this reason, Mbed
         TLS provides the configuration option
         MBEDTLS_PLATFORM_ZEROIZE_ALT, which allows users to configure
         mbedtls_platform_zeroize() to use a suitable implementation for
         their platform and needs

Parameters

buf	Buffer to be zeroized
len	Length of the buffer in bytes