File platform_util.h

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

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.

MBEDTLS_CHECK_RETURN

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.

MBEDTLS_IGNORE_RETURN(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.

Defines

MBEDTLS_CHECK_RETURN_CRITICAL

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.

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).

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.

Functions

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

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