xref: /qemu/tests/qtest/fuzz/generic_fuzz.c (revision da9bf5319838c193f92a3444bd3258b32c606980)

/*
 * Generic Virtual-Device Fuzzing Target
 *
 * Copyright Red Hat Inc., 2020
 *
 * Authors:
 *  Alexander Bulekov   <alxndr@bu.edu>
 *
 * This work is licensed under the terms of the GNU GPL, version 2 or later.
 * See the COPYING file in the top-level directory.
 */

#include "qemu/osdep.h"

#include <wordexp.h>

#include "hw/core/cpu.h"
#include "tests/qtest/libqos/libqtest.h"
#include "fuzz.h"
#include "fork_fuzz.h"
#include "exec/address-spaces.h"
#include "string.h"
#include "exec/memory.h"
#include "exec/ramblock.h"
#include "exec/address-spaces.h"
#include "hw/qdev-core.h"

/*
 * SEPARATOR is used to separate "operations" in the fuzz input
 */
#define SEPARATOR "FUZZ"

enum cmds {
    OP_IN,
    OP_OUT,
    OP_READ,
    OP_WRITE,
    OP_CLOCK_STEP,
};

#define DEFAULT_TIMEOUT_US 100000
#define USEC_IN_SEC 1000000000

typedef struct {
    ram_addr_t addr;
    ram_addr_t size; /* The number of bytes until the end of the I/O region */
} address_range;

static useconds_t timeout = DEFAULT_TIMEOUT_US;

static bool qtest_log_enabled;

/*
 * List of memory regions that are children of QOM objects specified by the
 * user for fuzzing.
 */
static GHashTable *fuzzable_memoryregions;

struct get_io_cb_info {
    int index;
    int found;
    address_range result;
};

static int get_io_address_cb(Int128 start, Int128 size,
                          const MemoryRegion *mr, void *opaque) {
    struct get_io_cb_info *info = opaque;
    if (g_hash_table_lookup(fuzzable_memoryregions, mr)) {
        if (info->index == 0) {
            info->result.addr = (ram_addr_t)start;
            info->result.size = (ram_addr_t)size;
            info->found = 1;
            return 1;
        }
        info->index--;
    }
    return 0;
}

/*
 * Here we want to convert a fuzzer-provided [io-region-index, offset] to
 * a physical address. To do this, we iterate over all of the matched
 * MemoryRegions. Check whether each region exists within the particular io
 * space. Return the absolute address of the offset within the index'th region
 * that is a subregion of the io_space and the distance until the end of the
 * memory region.
 */
static bool get_io_address(address_range *result, AddressSpace *as,
                            uint8_t index,
                            uint32_t offset) {
    FlatView *view;
    view = as->current_map;
    g_assert(view);
    struct get_io_cb_info cb_info = {};

    cb_info.index = index;

    /*
     * Loop around the FlatView until we match "index" number of
     * fuzzable_memoryregions, or until we know that there are no matching
     * memory_regions.
     */
    do {
        flatview_for_each_range(view, get_io_address_cb , &cb_info);
    } while (cb_info.index != index && !cb_info.found);

    *result = cb_info.result;
    return cb_info.found;
}

static bool get_pio_address(address_range *result,
                            uint8_t index, uint16_t offset)
{
    /*
     * PIO BARs can be set past the maximum port address (0xFFFF). Thus, result
     * can contain an addr that extends past the PIO space. When we pass this
     * address to qtest_in/qtest_out, it is cast to a uint16_t, so we might end
     * up fuzzing a completely different MemoryRegion/Device. Therefore, check
     * that the address here is within the PIO space limits.
     */
    bool found = get_io_address(result, &address_space_io, index, offset);
    return result->addr <= 0xFFFF ? found : false;
}

static bool get_mmio_address(address_range *result,
                             uint8_t index, uint32_t offset)
{
    return get_io_address(result, &address_space_memory, index, offset);
}

static void op_in(QTestState *s, const unsigned char * data, size_t len)
{
    enum Sizes {Byte, Word, Long, end_sizes};
    struct {
        uint8_t size;
        uint8_t base;
        uint16_t offset;
    } a;
    address_range abs;

    if (len < sizeof(a)) {
        return;
    }
    memcpy(&a, data, sizeof(a));
    if (get_pio_address(&abs, a.base, a.offset) == 0) {
        return;
    }

    switch (a.size %= end_sizes) {
    case Byte:
        qtest_inb(s, abs.addr);
        break;
    case Word:
        if (abs.size >= 2) {
            qtest_inw(s, abs.addr);
        }
        break;
    case Long:
        if (abs.size >= 4) {
            qtest_inl(s, abs.addr);
        }
        break;
    }
}

static void op_out(QTestState *s, const unsigned char * data, size_t len)
{
    enum Sizes {Byte, Word, Long, end_sizes};
    struct {
        uint8_t size;
        uint8_t base;
        uint16_t offset;
        uint32_t value;
    } a;
    address_range abs;

    if (len < sizeof(a)) {
        return;
    }
    memcpy(&a, data, sizeof(a));

    if (get_pio_address(&abs, a.base, a.offset) == 0) {
        return;
    }

    switch (a.size %= end_sizes) {
    case Byte:
        qtest_outb(s, abs.addr, a.value & 0xFF);
        break;
    case Word:
        if (abs.size >= 2) {
            qtest_outw(s, abs.addr, a.value & 0xFFFF);
        }
        break;
    case Long:
        if (abs.size >= 4) {
            qtest_outl(s, abs.addr, a.value);
        }
        break;
    }
}

static void op_read(QTestState *s, const unsigned char * data, size_t len)
{
    enum Sizes {Byte, Word, Long, Quad, end_sizes};
    struct {
        uint8_t size;
        uint8_t base;
        uint32_t offset;
    } a;
    address_range abs;

    if (len < sizeof(a)) {
        return;
    }
    memcpy(&a, data, sizeof(a));

    if (get_mmio_address(&abs, a.base, a.offset) == 0) {
        return;
    }

    switch (a.size %= end_sizes) {
    case Byte:
        qtest_readb(s, abs.addr);
        break;
    case Word:
        if (abs.size >= 2) {
            qtest_readw(s, abs.addr);
        }
        break;
    case Long:
        if (abs.size >= 4) {
            qtest_readl(s, abs.addr);
        }
        break;
    case Quad:
        if (abs.size >= 8) {
            qtest_readq(s, abs.addr);
        }
        break;
    }
}

static void op_write(QTestState *s, const unsigned char * data, size_t len)
{
    enum Sizes {Byte, Word, Long, Quad, end_sizes};
    struct {
        uint8_t size;
        uint8_t base;
        uint32_t offset;
        uint64_t value;
    } a;
    address_range abs;

    if (len < sizeof(a)) {
        return;
    }
    memcpy(&a, data, sizeof(a));

    if (get_mmio_address(&abs, a.base, a.offset) == 0) {
        return;
    }

    switch (a.size %= end_sizes) {
    case Byte:
            qtest_writeb(s, abs.addr, a.value & 0xFF);
        break;
    case Word:
        if (abs.size >= 2) {
            qtest_writew(s, abs.addr, a.value & 0xFFFF);
        }
        break;
    case Long:
        if (abs.size >= 4) {
            qtest_writel(s, abs.addr, a.value & 0xFFFFFFFF);
        }
        break;
    case Quad:
        if (abs.size >= 8) {
            qtest_writeq(s, abs.addr, a.value);
        }
        break;
    }
}

static void op_clock_step(QTestState *s, const unsigned char *data, size_t len)
{
    qtest_clock_step_next(s);
}

static void handle_timeout(int sig)
{
    if (qtest_log_enabled) {
        fprintf(stderr, "[Timeout]\n");
        fflush(stderr);
    }
    _Exit(0);
}

/*
 * Here, we interpret random bytes from the fuzzer, as a sequence of commands.
 * Some commands can be variable-width, so we use a separator, SEPARATOR, to
 * specify the boundaries between commands. SEPARATOR is used to separate
 * "operations" in the fuzz input. Why use a separator, instead of just using
 * the operations' length to identify operation boundaries?
 *   1. This is a simple way to support variable-length operations
 *   2. This adds "stability" to the input.
 *      For example take the input "AbBcgDefg", where there is no separator and
 *      Opcodes are capitalized.
 *      Simply, by removing the first byte, we end up with a very different
 *      sequence:
 *      BbcGdefg...
 *      By adding a separator, we avoid this problem:
 *      Ab SEP Bcg SEP Defg -> B SEP Bcg SEP Defg
 *      Since B uses two additional bytes as operands, the first "B" will be
 *      ignored. The fuzzer actively tries to reduce inputs, so such unused
 *      bytes are likely to be pruned, eventually.
 *
 *  SEPARATOR is trivial for the fuzzer to discover when using ASan. Optionally,
 *  SEPARATOR can be manually specified as a dictionary value (see libfuzzer's
 *  -dict), though this should not be necessary.
 *
 * As a result, the stream of bytes is converted into a sequence of commands.
 * In a simplified example where SEPARATOR is 0xFF:
 * 00 01 02 FF 03 04 05 06 FF 01 FF ...
 * becomes this sequence of commands:
 * 00 01 02    -> op00 (0102)   -> in (0102, 2)
 * 03 04 05 06 -> op03 (040506) -> write (040506, 3)
 * 01          -> op01 (-,0)    -> out (-,0)
 * ...
 *
 * Note here that it is the job of the individual opcode functions to check
 * that enough data was provided. I.e. in the last command out (,0), out needs
 * to check that there is not enough data provided to select an address/value
 * for the operation.
 */
static void generic_fuzz(QTestState *s, const unsigned char *Data, size_t Size)
{
    void (*ops[]) (QTestState *s, const unsigned char* , size_t) = {
        [OP_IN]                 = op_in,
        [OP_OUT]                = op_out,
        [OP_READ]               = op_read,
        [OP_WRITE]              = op_write,
        [OP_CLOCK_STEP]         = op_clock_step,
    };
    const unsigned char *cmd = Data;
    const unsigned char *nextcmd;
    size_t cmd_len;
    uint8_t op;

    if (fork() == 0) {
        /*
         * Sometimes the fuzzer will find inputs that take quite a long time to
         * process. Often times, these inputs do not result in new coverage.
         * Even if these inputs might be interesting, they can slow down the
         * fuzzer, overall. Set a timeout to avoid hurting performance, too much
         */
        if (timeout) {
            struct sigaction sact;
            struct itimerval timer;

            sigemptyset(&sact.sa_mask);
            sact.sa_flags   = SA_NODEFER;
            sact.sa_handler = handle_timeout;
            sigaction(SIGALRM, &sact, NULL);

            memset(&timer, 0, sizeof(timer));
            timer.it_value.tv_sec = timeout / USEC_IN_SEC;
            timer.it_value.tv_usec = timeout % USEC_IN_SEC;
            setitimer(ITIMER_VIRTUAL, &timer, NULL);
        }

        while (cmd && Size) {
            /* Get the length until the next command or end of input */
            nextcmd = memmem(cmd, Size, SEPARATOR, strlen(SEPARATOR));
            cmd_len = nextcmd ? nextcmd - cmd : Size;

            if (cmd_len > 0) {
                /* Interpret the first byte of the command as an opcode */
                op = *cmd % (sizeof(ops) / sizeof((ops)[0]));
                ops[op](s, cmd + 1, cmd_len - 1);

                /* Run the main loop */
                flush_events(s);
            }
            /* Advance to the next command */
            cmd = nextcmd ? nextcmd + sizeof(SEPARATOR) - 1 : nextcmd;
            Size = Size - (cmd_len + sizeof(SEPARATOR) - 1);
        }
        _Exit(0);
    } else {
        flush_events(s);
        wait(0);
    }
}

static void usage(void)
{
    printf("Please specify the following environment variables:\n");
    printf("QEMU_FUZZ_ARGS= the command line arguments passed to qemu\n");
    printf("QEMU_FUZZ_OBJECTS= "
            "a space separated list of QOM type names for objects to fuzz\n");
    printf("Optionally: QEMU_FUZZ_TIMEOUT= Specify a custom timeout (us). "
            "0 to disable. %d by default\n", timeout);
    exit(0);
}

static int locate_fuzz_memory_regions(Object *child, void *opaque)
{
    const char *name;
    MemoryRegion *mr;
    if (object_dynamic_cast(child, TYPE_MEMORY_REGION)) {
        mr = MEMORY_REGION(child);
        if ((memory_region_is_ram(mr) ||
            memory_region_is_ram_device(mr) ||
            memory_region_is_rom(mr)) == false) {
            name = object_get_canonical_path_component(child);
            /*
             * We don't want duplicate pointers to the same MemoryRegion, so
             * try to remove copies of the pointer, before adding it.
             */
            g_hash_table_insert(fuzzable_memoryregions, mr, (gpointer)true);
        }
    }
    return 0;
}

static int locate_fuzz_objects(Object *child, void *opaque)
{
    char *pattern = opaque;
    if (g_pattern_match_simple(pattern, object_get_typename(child))) {
        /* Find and save ptrs to any child MemoryRegions */
        object_child_foreach_recursive(child, locate_fuzz_memory_regions, NULL);

    } else if (object_dynamic_cast(OBJECT(child), TYPE_MEMORY_REGION)) {
        if (g_pattern_match_simple(pattern,
            object_get_canonical_path_component(child))) {
            MemoryRegion *mr;
            mr = MEMORY_REGION(child);
            if ((memory_region_is_ram(mr) ||
                 memory_region_is_ram_device(mr) ||
                 memory_region_is_rom(mr)) == false) {
                g_hash_table_insert(fuzzable_memoryregions, mr, (gpointer)true);
            }
        }
    }
    return 0;
}

static void generic_pre_fuzz(QTestState *s)
{
    GHashTableIter iter;
    MemoryRegion *mr;
    char **result;

    if (!getenv("QEMU_FUZZ_OBJECTS")) {
        usage();
    }
    if (getenv("QTEST_LOG")) {
        qtest_log_enabled = 1;
    }
    if (getenv("QEMU_FUZZ_TIMEOUT")) {
        timeout = g_ascii_strtoll(getenv("QEMU_FUZZ_TIMEOUT"), NULL, 0);
    }

    fuzzable_memoryregions = g_hash_table_new(NULL, NULL);

    result = g_strsplit(getenv("QEMU_FUZZ_OBJECTS"), " ", -1);
    for (int i = 0; result[i] != NULL; i++) {
        printf("Matching objects by name %s\n", result[i]);
        object_child_foreach_recursive(qdev_get_machine(),
                                    locate_fuzz_objects,
                                    result[i]);
    }
    g_strfreev(result);
    printf("This process will try to fuzz the following MemoryRegions:\n");

    g_hash_table_iter_init(&iter, fuzzable_memoryregions);
    while (g_hash_table_iter_next(&iter, (gpointer)&mr, NULL)) {
        printf("  * %s (size %lx)\n",
               object_get_canonical_path_component(&(mr->parent_obj)),
               (uint64_t)mr->size);
    }

    if (!g_hash_table_size(fuzzable_memoryregions)) {
        printf("No fuzzable memory regions found...\n");
        exit(1);
    }

    counter_shm_init();
}

static GString *generic_fuzz_cmdline(FuzzTarget *t)
{
    GString *cmd_line = g_string_new(TARGET_NAME);
    if (!getenv("QEMU_FUZZ_ARGS")) {
        usage();
    }
    g_string_append_printf(cmd_line, " -display none \
                                      -machine accel=qtest, \
                                      -m 512M %s ", getenv("QEMU_FUZZ_ARGS"));
    return cmd_line;
}

static void register_generic_fuzz_targets(void)
{
    fuzz_add_target(&(FuzzTarget){
            .name = "generic-fuzz",
            .description = "Fuzz based on any qemu command-line args. ",
            .get_init_cmdline = generic_fuzz_cmdline,
            .pre_fuzz = generic_pre_fuzz,
            .fuzz = generic_fuzz,
    });
}

fuzz_target_init(register_generic_fuzz_targets);