zircon/kernel/dev/hw_rng/debug.cpp

// Copyright 2016 The Fuchsia Authors
// Copyright (c) 2016, Google, Inc. All rights reserved
//
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file or at
// https://opensource.org/licenses/MIT

#include <dev/hw_rng.h>

#include <debug.h>
#include <fbl/algorithm.h>
#include <lib/console.h>
#include <stdlib.h>

static int cmd_rng32(int argc, const cmd_args* argv, uint32_t flags) {
    uint32_t val;
    __UNUSED size_t fetched;

    fetched = hw_rng_get_entropy(&val, sizeof(val), true);

    if (fetched == 0) {
        printf("hw rng failed. Support may not exist on this platform\n");
        return ZX_ERR_NOT_SUPPORTED;
    }

    DEBUG_ASSERT(fetched == sizeof(val));

    printf("Random val = %u (0x%08x)\n", val, val);

    return ZX_OK;
}

static int cmd_rng(int argc, const cmd_args* argv, uint32_t flags) {
    if ((argc < 2) || (argc > 3)) {
        printf("Invalid argument count\n\n"
               "Usage : %s <N> [wait]\n"
               "N     : Number of bytes to generate.\n"
               "wait  : true  -> wait indefinitely for bytes to be generated\n"
               "      : false -> terminate if HW generator runs out of entropy (default)\n",
               argv[0].str);
        return ZX_ERR_INVALID_ARGS;
    }

    printf("Generating %lu random bytes\n", argv[1].u);

    size_t offset = 0;
    bool wait = (argc == 3) ? argv[2].b : false;
    while (offset < argv[1].u) {
        uint8_t bytes[16];
        size_t todo, done;

        todo = fbl::min(sizeof(bytes), argv[1].u - offset);
        done = hw_rng_get_entropy(bytes, todo, wait);
        DEBUG_ASSERT(done <= todo);

        hexdump8_ex(bytes, done, offset);
        offset += done;

        if (done < todo) {
            printf("Entropy exhausted after %zu byte%s\n",
                   offset, offset == 1 ? "" : "s");
            break;
        }
    }

    return ZX_OK;
}

STATIC_COMMAND_START
STATIC_COMMAND("rng32",
               "Generate and print a random 32 bit unsigned integer using the HW RNG",
               &cmd_rng32)
STATIC_COMMAND("rng",
               "Generate and print N random bytes using the HW RNG",
               &cmd_rng)
STATIC_COMMAND_END(hw_rng)