tests/src/threading_helpers.c

/** Mutex usage verification framework. */

/*
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
 */

#include <test/helpers.h>
#include <test/macros.h>

#if defined(MBEDTLS_TEST_MUTEX_USAGE)

#include "mbedtls/threading.h"

/** Mutex usage verification framework.
 *
 * The mutex usage verification code below aims to detect bad usage of
 * Mbed TLS's mutex abstraction layer at runtime. Note that this is solely
 * about the use of the mutex itself, not about checking whether the mutex
 * correctly protects whatever it is supposed to protect.
 *
 * The normal usage of a mutex is:
 * ```
 * digraph mutex_states {
 *   "UNINITIALIZED"; // the initial state
 *   "IDLE";
 *   "FREED";
 *   "LOCKED";
 *   "UNINITIALIZED" -> "IDLE" [label="init"];
 *   "FREED" -> "IDLE" [label="init"];
 *   "IDLE" -> "LOCKED" [label="lock"];
 *   "LOCKED" -> "IDLE" [label="unlock"];
 *   "IDLE" -> "FREED" [label="free"];
 * }
 * ```
 *
 * All bad transitions that can be unambiguously detected are reported.
 * An attempt to use an uninitialized mutex cannot be detected in general
 * since the memory content may happen to denote a valid state. For the same
 * reason, a double init cannot be detected.
 * All-bits-zero is the state of a freed mutex, which is distinct from an
 * initialized mutex, so attempting to use zero-initialized memory as a mutex
 * without calling the init function is detected.
 *
 * The framework attempts to detect missing calls to init and free by counting
 * calls to init and free. If there are more calls to init than free, this
 * means that a mutex is not being freed somewhere, which is a memory leak
 * on platforms where a mutex consumes resources other than the
 * mbedtls_threading_mutex_t object itself. If there are more calls to free
 * than init, this indicates a missing init, which is likely to be detected
 * by an attempt to lock the mutex as well. A limitation of this framework is
 * that it cannot detect scenarios where there is exactly the same number of
 * calls to init and free but the calls don't match. A bug like this is
 * unlikely to happen uniformly throughout the whole test suite though.
 *
 * If an error is detected, this framework will report what happened and the
 * test case will be marked as failed. Unfortunately, the error report cannot
 * indicate the exact location of the problematic call. To locate the error,
 * use a debugger and set a breakpoint on mbedtls_test_mutex_usage_error().
 */
enum value_of_mutex_is_valid_field {
    /* Potential values for the is_valid field of mbedtls_threading_mutex_t.
     * Note that MUTEX_FREED must be 0 and MUTEX_IDLE must be 1 for
     * compatibility with threading_mutex_init_pthread() and
     * threading_mutex_free_pthread(). MUTEX_LOCKED could be any nonzero
     * value. */
    MUTEX_FREED = 0, //! < Set by mbedtls_test_wrap_mutex_free
    MUTEX_IDLE = 1, //! < Set by mbedtls_test_wrap_mutex_init and by mbedtls_test_wrap_mutex_unlock
    MUTEX_LOCKED = 2, //! < Set by mbedtls_test_wrap_mutex_lock
};

typedef struct {
    void (*init)(mbedtls_threading_mutex_t *);
    void (*free)(mbedtls_threading_mutex_t *);
    int (*lock)(mbedtls_threading_mutex_t *);
    int (*unlock)(mbedtls_threading_mutex_t *);
} mutex_functions_t;
static mutex_functions_t mutex_functions;

/** The total number of calls to mbedtls_mutex_init(), minus the total number
 * of calls to mbedtls_mutex_free().
 *
 * Reset to 0 after each test case.
 */
static int live_mutexes;

static void mbedtls_test_mutex_usage_error(mbedtls_threading_mutex_t *mutex,
                                           const char *msg)
{
    (void) mutex;
    if (mbedtls_test_info.mutex_usage_error == NULL) {
        mbedtls_test_info.mutex_usage_error = msg;
    }
    mbedtls_fprintf(stdout, "[mutex: %s] ", msg);
    /* Don't mark the test as failed yet. This way, if the test fails later
     * for a functional reason, the test framework will report the message
     * and location for this functional reason. If the test passes,
     * mbedtls_test_mutex_usage_check() will mark it as failed. */
}

static void mbedtls_test_wrap_mutex_init(mbedtls_threading_mutex_t *mutex)
{
    mutex_functions.init(mutex);

    if (mutex_functions.lock(&mbedtls_test_mutex_mutex) == 0) {
        mutex->state = MUTEX_IDLE;
        ++live_mutexes;

        mutex_functions.unlock(&mbedtls_test_mutex_mutex);
    }
}

static void mbedtls_test_wrap_mutex_free(mbedtls_threading_mutex_t *mutex)
{
    switch (mutex->is_valid) {
        case MUTEX_FREED:
            mbedtls_test_mutex_usage_error(mutex, "free without init or double free");
            break;
        case MUTEX_IDLE:
            /* Do nothing. The underlying free function will reset is_valid
             * to 0. */
            break;
        case MUTEX_LOCKED:
            mbedtls_test_mutex_usage_error(mutex, "free without unlock");
            break;
        default:
            mbedtls_test_mutex_usage_error(mutex, "corrupted state");
            break;
    }

    /* Mark mutex as free'd first, because we need to release the mutex. If
     * free fails, this could end up with inconsistent state. */
    if (mutex->is_valid) {
        mutex->is_valid = MUTEX_FREED;
        --live_mutexes;
    }
    mutex_functions.free(mutex);
}

static int mbedtls_test_wrap_mutex_lock(mbedtls_threading_mutex_t *mutex)
{
    int ret = mutex_functions.lock(mutex);
    switch (mutex->is_valid) {
        case MUTEX_FREED:
            mbedtls_test_mutex_usage_error(mutex, "lock without init");
            break;
        case MUTEX_IDLE:
            if (ret == 0) {
                mutex->is_valid = MUTEX_LOCKED;
            }
            break;
        case MUTEX_LOCKED:
            mbedtls_test_mutex_usage_error(mutex, "double lock");
            break;
        default:
            mbedtls_test_mutex_usage_error(mutex, "corrupted state");
            break;
    }
    return ret;
}

static int mbedtls_test_wrap_mutex_unlock(mbedtls_threading_mutex_t *mutex)
{
    int ret = mutex_functions.unlock(mutex);
    switch (mutex->is_valid) {
        case MUTEX_FREED:
            mbedtls_test_mutex_usage_error(mutex, "unlock without init");
            break;
        case MUTEX_IDLE:
            mbedtls_test_mutex_usage_error(mutex, "unlock without lock");
            break;
        case MUTEX_LOCKED:
            if (ret == 0) {
                mutex->is_valid = MUTEX_IDLE;
            }
            break;
        default:
            mbedtls_test_mutex_usage_error(mutex, "corrupted state");
            break;
    }
    return ret;
}

void mbedtls_test_mutex_usage_init(void)
{
    mutex_functions.init = mbedtls_mutex_init;
    mutex_functions.free = mbedtls_mutex_free;
    mutex_functions.lock = mbedtls_mutex_lock;
    mutex_functions.unlock = mbedtls_mutex_unlock;
    mbedtls_mutex_init = &mbedtls_test_wrap_mutex_init;
    mbedtls_mutex_free = &mbedtls_test_wrap_mutex_free;
    mbedtls_mutex_lock = &mbedtls_test_wrap_mutex_lock;
    mbedtls_mutex_unlock = &mbedtls_test_wrap_mutex_unlock;
}

void mbedtls_test_mutex_usage_check(void)
{
    if (live_mutexes != 0) {
        /* A positive number (more init than free) means that a mutex resource
         * is leaking (on platforms where a mutex consumes more than the
         * mbedtls_threading_mutex_t object itself). The rare case of a
         * negative number means a missing init somewhere. */
        mbedtls_fprintf(stdout, "[mutex: %d leaked] ", live_mutexes);
        live_mutexes = 0;
        if (mbedtls_test_info.mutex_usage_error == NULL) {
            mbedtls_test_info.mutex_usage_error = "missing free";
        }
    }
    if (mbedtls_test_info.mutex_usage_error != NULL &&
        mbedtls_test_info.result != MBEDTLS_TEST_RESULT_FAILED) {
        /* Functionally, the test passed. But there was a mutex usage error,
         * so mark the test as failed after all. */
        mbedtls_test_fail("Mutex usage error", __LINE__, __FILE__);
    }
    mbedtls_test_info.mutex_usage_error = NULL;
}

#endif /* MBEDTLS_TEST_MUTEX_USAGE */