1 files changed, 1043 insertions, 0 deletions
diff --git a/tests/qtest/fuzz/generic_fuzz.c b/tests/qtest/fuzz/generic_fuzz.c
new file mode 100644
index 000000000..dd7e25851
--- /dev/null
+++ b/tests/qtest/fuzz/generic_fuzz.c
@@ -0,0 +1,1043 @@
+/*
+ * 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 "tests/qtest/libqos/pci-pc.h"
+#include "fuzz.h"
+#include "fork_fuzz.h"
+#include "string.h"
+#include "exec/memory.h"
+#include "exec/ramblock.h"
+#include "hw/qdev-core.h"
+#include "hw/pci/pci.h"
+#include "hw/boards.h"
+#include "generic_fuzz_configs.h"
+#include "hw/mem/sparse-mem.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_PCI_READ,
+    OP_PCI_WRITE,
+    OP_DISABLE_PCI,
+    OP_ADD_DMA_PATTERN,
+    OP_CLEAR_DMA_PATTERNS,
+    OP_CLOCK_STEP,
+};
+
+#define DEFAULT_TIMEOUT_US 100000
+#define USEC_IN_SEC 1000000000
+
+#define MAX_DMA_FILL_SIZE 0x10000
+
+#define PCI_HOST_BRIDGE_CFG 0xcf8
+#define PCI_HOST_BRIDGE_DATA 0xcfc
+
+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;
+
+MemoryRegion *sparse_mem_mr;
+
+/*
+ * A pattern used to populate a DMA region or perform a memwrite. This is
+ * useful for e.g. populating tables of unique addresses.
+ * Example {.index = 1; .stride = 2; .len = 3; .data = "\x00\x01\x02"}
+ * Renders as: 00 01 02   00 03 02   00 05 02   00 07 02 ...
+ */
+typedef struct {
+    uint8_t index;      /* Index of a byte to increment by stride */
+    uint8_t stride;     /* Increment each index'th byte by this amount */
+    size_t len;
+    const uint8_t *data;
+} pattern;
+
+/* Avoid filling the same DMA region between MMIO/PIO commands ? */
+static bool avoid_double_fetches;
+
+static QTestState *qts_global; /* Need a global for the DMA callback */
+
+/*
+ * List of memory regions that are children of QOM objects specified by the
+ * user for fuzzing.
+ */
+static GHashTable *fuzzable_memoryregions;
+static GPtrArray *fuzzable_pci_devices;
+
+struct get_io_cb_info {
+    int index;
+    int found;
+    address_range result;
+};
+
+static bool get_io_address_cb(Int128 start, Int128 size,
+                              const MemoryRegion *mr,
+                              hwaddr offset_in_region,
+                              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 true;
+        }
+        info->index--;
+    }
+    return false;
+}
+
+/*
+ * List of dma regions populated since the last fuzzing command. Used to ensure
+ * that we only write to each DMA address once, to avoid race conditions when
+ * building reproducers.
+ */
+static GArray *dma_regions;
+
+static GArray *dma_patterns;
+static int dma_pattern_index;
+static bool pci_disabled;
+
+/*
+ * Allocate a block of memory and populate it with a pattern.
+ */
+static void *pattern_alloc(pattern p, size_t len)
+{
+    int i;
+    uint8_t *buf = g_malloc(len);
+    uint8_t sum = 0;
+
+    for (i = 0; i < len; ++i) {
+        buf[i] = p.data[i % p.len];
+        if ((i % p.len) == p.index) {
+            buf[i] += sum;
+            sum += p.stride;
+        }
+    }
+    return buf;
+}
+
+static int memory_access_size(MemoryRegion *mr, unsigned l, hwaddr addr)
+{
+    unsigned access_size_max = mr->ops->valid.max_access_size;
+
+    /*
+     * Regions are assumed to support 1-4 byte accesses unless
+     * otherwise specified.
+     */
+    if (access_size_max == 0) {
+        access_size_max = 4;
+    }
+
+    /* Bound the maximum access by the alignment of the address.  */
+    if (!mr->ops->impl.unaligned) {
+        unsigned align_size_max = addr & -addr;
+        if (align_size_max != 0 && align_size_max < access_size_max) {
+            access_size_max = align_size_max;
+        }
+    }
+
+    /* Don't attempt accesses larger than the maximum.  */
+    if (l > access_size_max) {
+        l = access_size_max;
+    }
+    l = pow2floor(l);
+
+    return l;
+}
+
+/*
+ * Call-back for functions that perform DMA reads from guest memory. Confirm
+ * that the region has not already been populated since the last loop in
+ * generic_fuzz(), avoiding potential race-conditions, which we don't have
+ * a good way for reproducing right now.
+ */
+void fuzz_dma_read_cb(size_t addr, size_t len, MemoryRegion *mr)
+{
+    /* Are we in the generic-fuzzer or are we using another fuzz-target? */
+    if (!qts_global) {
+        return;
+    }
+
+    /*
+     * Return immediately if:
+     * - We have no DMA patterns defined
+     * - The length of the DMA read request is zero
+     * - The DMA read is hitting an MR other than the machine's main RAM
+     * - The DMA request hits past the bounds of our RAM
+     */
+    if (dma_patterns->len == 0
+        || len == 0
+        || (mr != current_machine->ram && mr != sparse_mem_mr)) {
+        return;
+    }
+
+    /*
+     * If we overlap with any existing dma_regions, split the range and only
+     * populate the non-overlapping parts.
+     */
+    address_range region;
+    bool double_fetch = false;
+    for (int i = 0;
+         i < dma_regions->len && (avoid_double_fetches || qtest_log_enabled);
+         ++i) {
+        region = g_array_index(dma_regions, address_range, i);
+        if (addr < region.addr + region.size && addr + len > region.addr) {
+            double_fetch = true;
+            if (addr < region.addr
+                && avoid_double_fetches) {
+                fuzz_dma_read_cb(addr, region.addr - addr, mr);
+            }
+            if (addr + len > region.addr + region.size
+                && avoid_double_fetches) {
+                fuzz_dma_read_cb(region.addr + region.size,
+                        addr + len - (region.addr + region.size), mr);
+            }
+            return;
+        }
+    }
+
+    /* Cap the length of the DMA access to something reasonable */
+    len = MIN(len, MAX_DMA_FILL_SIZE);
+
+    address_range ar = {addr, len};
+    g_array_append_val(dma_regions, ar);
+    pattern p = g_array_index(dma_patterns, pattern, dma_pattern_index);
+    void *buf_base = pattern_alloc(p, ar.size);
+    void *buf = buf_base;
+    hwaddr l, addr1;
+    MemoryRegion *mr1;
+    while (len > 0) {
+        l = len;
+        mr1 = address_space_translate(first_cpu->as,
+                                      addr, &addr1, &l, true,
+                                      MEMTXATTRS_UNSPECIFIED);
+
+        /*
+         *  If mr1 isn't RAM, address_space_translate doesn't update l. Use
+         *  memory_access_size to identify the number of bytes that it is safe
+         *  to write without accidentally writing to another MemoryRegion.
+         */
+        if (!memory_region_is_ram(mr1)) {
+            l = memory_access_size(mr1, l, addr1);
+        }
+        if (memory_region_is_ram(mr1) ||
+            memory_region_is_romd(mr1) ||
+            mr1 == sparse_mem_mr) {
+            /* ROM/RAM case */
+            if (qtest_log_enabled) {
+                /*
+                * With QTEST_LOG, use a normal, slow QTest memwrite. Prefix the log
+                * that will be written by qtest.c with a DMA tag, so we can reorder
+                * the resulting QTest trace so the DMA fills precede the last PIO/MMIO
+                * command.
+                */
+                fprintf(stderr, "[DMA] ");
+                if (double_fetch) {
+                    fprintf(stderr, "[DOUBLE-FETCH] ");
+                }
+                fflush(stderr);
+            }
+            qtest_memwrite(qts_global, addr, buf, l);
+        }
+        len -= l;
+        buf += l;
+        addr += l;
+
+    }
+    g_free(buf_base);
+
+    /* Increment the index of the pattern for the next DMA access */
+    dma_pattern_index = (dma_pattern_index + 1) % dma_patterns->len;
+}
+
+/*
+ * 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;
+    if (result->size) {
+        offset = offset % result->size;
+        result->addr += offset;
+        result->size -= offset;
+    }
+    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_pci_read(QTestState *s, const unsigned char * data, size_t len)
+{
+    enum Sizes {Byte, Word, Long, end_sizes};
+    struct {
+        uint8_t size;
+        uint8_t base;
+        uint8_t offset;
+    } a;
+    if (len < sizeof(a) || fuzzable_pci_devices->len == 0 || pci_disabled) {
+        return;
+    }
+    memcpy(&a, data, sizeof(a));
+    PCIDevice *dev = g_ptr_array_index(fuzzable_pci_devices,
+                                  a.base % fuzzable_pci_devices->len);
+    int devfn = dev->devfn;
+    qtest_outl(s, PCI_HOST_BRIDGE_CFG, (1U << 31) | (devfn << 8) | a.offset);
+    switch (a.size %= end_sizes) {
+    case Byte:
+        qtest_inb(s, PCI_HOST_BRIDGE_DATA);
+        break;
+    case Word:
+        qtest_inw(s, PCI_HOST_BRIDGE_DATA);
+        break;
+    case Long:
+        qtest_inl(s, PCI_HOST_BRIDGE_DATA);
+        break;
+    }
+}
+
+static void op_pci_write(QTestState *s, const unsigned char * data, size_t len)
+{
+    enum Sizes {Byte, Word, Long, end_sizes};
+    struct {
+        uint8_t size;
+        uint8_t base;
+        uint8_t offset;
+        uint32_t value;
+    } a;
+    if (len < sizeof(a) || fuzzable_pci_devices->len == 0 || pci_disabled) {
+        return;
+    }
+    memcpy(&a, data, sizeof(a));
+    PCIDevice *dev = g_ptr_array_index(fuzzable_pci_devices,
+                                  a.base % fuzzable_pci_devices->len);
+    int devfn = dev->devfn;
+    qtest_outl(s, PCI_HOST_BRIDGE_CFG, (1U << 31) | (devfn << 8) | a.offset);
+    switch (a.size %= end_sizes) {
+    case Byte:
+        qtest_outb(s, PCI_HOST_BRIDGE_DATA, a.value & 0xFF);
+        break;
+    case Word:
+        qtest_outw(s, PCI_HOST_BRIDGE_DATA, a.value & 0xFFFF);
+        break;
+    case Long:
+        qtest_outl(s, PCI_HOST_BRIDGE_DATA, a.value & 0xFFFFFFFF);
+        break;
+    }
+}
+
+static void op_add_dma_pattern(QTestState *s,
+                               const unsigned char *data, size_t len)
+{
+    struct {
+        /*
+         * index and stride can be used to increment the index-th byte of the
+         * pattern by the value stride, for each loop of the pattern.
+         */
+        uint8_t index;
+        uint8_t stride;
+    } a;
+
+    if (len < sizeof(a) + 1) {
+        return;
+    }
+    memcpy(&a, data, sizeof(a));
+    pattern p = {a.index, a.stride, len - sizeof(a), data + sizeof(a)};
+    p.index = a.index % p.len;
+    g_array_append_val(dma_patterns, p);
+    return;
+}
+
+static void op_clear_dma_patterns(QTestState *s,
+                                  const unsigned char *data, size_t len)
+{
+    g_array_set_size(dma_patterns, 0);
+    dma_pattern_index = 0;
+}
+
+static void op_clock_step(QTestState *s, const unsigned char *data, size_t len)
+{
+    qtest_clock_step_next(s);
+}
+
+static void op_disable_pci(QTestState *s, const unsigned char *data, size_t len)
+{
+    pci_disabled = true;
+}
+
+static void handle_timeout(int sig)
+{
+    if (qtest_log_enabled) {
+        fprintf(stderr, "[Timeout]\n");
+        fflush(stderr);
+    }
+
+    /*
+     * If there is a crash, libfuzzer/ASAN forks a child to run an
+     * "llvm-symbolizer" process for printing out a pretty stacktrace. It
+     * communicates with this child using a pipe.  If we timeout+Exit, while
+     * libfuzzer is still communicating with the llvm-symbolizer child, we will
+     * be left with an orphan llvm-symbolizer process. Sometimes, this appears
+     * to lead to a deadlock in the forkserver. Use waitpid to check if there
+     * are any waitable children. If so, exit out of the signal-handler, and
+     * let libfuzzer finish communicating with the child, and exit, on its own.
+     */
+    if (waitpid(-1, NULL, WNOHANG) == 0) {
+        return;
+    }
+
+    _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_PCI_READ]           = op_pci_read,
+        [OP_PCI_WRITE]          = op_pci_write,
+        [OP_DISABLE_PCI]        = op_disable_pci,
+        [OP_ADD_DMA_PATTERN]    = op_add_dma_pattern,
+        [OP_CLEAR_DMA_PATTERNS] = op_clear_dma_patterns,
+        [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) {
+        struct sigaction sact;
+        struct itimerval timer;
+        sigset_t set;
+        /*
+         * 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 for each command to avoid hurting
+         * performance, too much
+         */
+        if (timeout) {
+
+            sigemptyset(&sact.sa_mask);
+            sact.sa_flags   = SA_NODEFER;
+            sact.sa_handler = handle_timeout;
+            sigaction(SIGALRM, &sact, NULL);
+
+            sigemptyset(&set);
+            sigaddset(&set, SIGALRM);
+            pthread_sigmask(SIG_UNBLOCK, &set, NULL);
+
+            memset(&timer, 0, sizeof(timer));
+            timer.it_value.tv_sec = timeout / USEC_IN_SEC;
+            timer.it_value.tv_usec = timeout % USEC_IN_SEC;
+        }
+
+        op_clear_dma_patterns(s, NULL, 0);
+        pci_disabled = false;
+
+        while (cmd && Size) {
+            /* Reset the timeout, each time we run a new command */
+            if (timeout) {
+                setitimer(ITIMER_REAL, &timer, NULL);
+            }
+
+            /* 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);
+            g_array_set_size(dma_regions, 0);
+        }
+        _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_AVOID_DOUBLE_FETCH= "
+            "Try to avoid racy DMA double fetch bugs? %d by default\n",
+            avoid_double_fetches);
+    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)
+{
+    GString *type_name;
+    GString *path_name;
+    char *pattern = opaque;
+
+    type_name = g_string_new(object_get_typename(child));
+    g_string_ascii_down(type_name);
+    if (g_pattern_match_simple(pattern, type_name->str)) {
+        /* Find and save ptrs to any child MemoryRegions */
+        object_child_foreach_recursive(child, locate_fuzz_memory_regions, NULL);
+
+        /*
+         * We matched an object. If its a PCI device, store a pointer to it so
+         * we can map BARs and fuzz its config space.
+         */
+        if (object_dynamic_cast(OBJECT(child), TYPE_PCI_DEVICE)) {
+            /*
+             * Don't want duplicate pointers to the same PCIDevice, so remove
+             * copies of the pointer, before adding it.
+             */
+            g_ptr_array_remove_fast(fuzzable_pci_devices, PCI_DEVICE(child));
+            g_ptr_array_add(fuzzable_pci_devices, PCI_DEVICE(child));
+        }
+    } else if (object_dynamic_cast(OBJECT(child), TYPE_MEMORY_REGION)) {
+        path_name = g_string_new(object_get_canonical_path_component(child));
+        g_string_ascii_down(path_name);
+        if (g_pattern_match_simple(pattern, path_name->str)) {
+            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);
+            }
+        }
+        g_string_free(path_name, true);
+    }
+    g_string_free(type_name, true);
+    return 0;
+}
+
+
+static void pci_enum(gpointer pcidev, gpointer bus)
+{
+    PCIDevice *dev = pcidev;
+    QPCIDevice *qdev;
+    int i;
+
+    qdev = qpci_device_find(bus, dev->devfn);
+    g_assert(qdev != NULL);
+    for (i = 0; i < 6; i++) {
+        if (dev->io_regions[i].size) {
+            qpci_iomap(qdev, i, NULL);
+        }
+    }
+    qpci_device_enable(qdev);
+    g_free(qdev);
+}
+
+static void generic_pre_fuzz(QTestState *s)
+{
+    GHashTableIter iter;
+    MemoryRegion *mr;
+    QPCIBus *pcibus;
+    char **result;
+    GString *name_pattern;
+
+    if (!getenv("QEMU_FUZZ_OBJECTS")) {
+        usage();
+    }
+    if (getenv("QTEST_LOG")) {
+        qtest_log_enabled = 1;
+    }
+    if (getenv("QEMU_AVOID_DOUBLE_FETCH")) {
+        avoid_double_fetches = 1;
+    }
+    if (getenv("QEMU_FUZZ_TIMEOUT")) {
+        timeout = g_ascii_strtoll(getenv("QEMU_FUZZ_TIMEOUT"), NULL, 0);
+    }
+    qts_global = s;
+
+    /*
+     * Create a special device that we can use to back DMA buffers at very
+     * high memory addresses
+     */
+    sparse_mem_mr = sparse_mem_init(0, UINT64_MAX);
+
+    dma_regions = g_array_new(false, false, sizeof(address_range));
+    dma_patterns = g_array_new(false, false, sizeof(pattern));
+
+    fuzzable_memoryregions = g_hash_table_new(NULL, NULL);
+    fuzzable_pci_devices   = g_ptr_array_new();
+
+    result = g_strsplit(getenv("QEMU_FUZZ_OBJECTS"), " ", -1);
+    for (int i = 0; result[i] != NULL; i++) {
+        name_pattern = g_string_new(result[i]);
+        /*
+         * Make the pattern lowercase. We do the same for all the MemoryRegion
+         * and Type names so the configs are case-insensitive.
+         */
+        g_string_ascii_down(name_pattern);
+        printf("Matching objects by name %s\n", result[i]);
+        object_child_foreach_recursive(qdev_get_machine(),
+                                    locate_fuzz_objects,
+                                    name_pattern->str);
+        g_string_free(name_pattern, true);
+    }
+    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 0x%" PRIx64 ")\n",
+               object_get_canonical_path_component(&(mr->parent_obj)),
+               memory_region_size(mr));
+    }
+
+    if (!g_hash_table_size(fuzzable_memoryregions)) {
+        printf("No fuzzable memory regions found...\n");
+        exit(1);
+    }
+
+    pcibus = qpci_new_pc(s, NULL);
+    g_ptr_array_foreach(fuzzable_pci_devices, pci_enum, pcibus);
+    qpci_free_pc(pcibus);
+
+    counter_shm_init();
+}
+
+/*
+ * When libfuzzer gives us two inputs to combine, return a new input with the
+ * following structure:
+ *
+ * Input 1 (data1)
+ * SEPARATOR
+ * Clear out the DMA Patterns
+ * SEPARATOR
+ * Disable the pci_read/write instructions
+ * SEPARATOR
+ * Input 2 (data2)
+ *
+ * The idea is to collate the core behaviors of the two inputs.
+ * For example:
+ * Input 1: maps a device's BARs, sets up three DMA patterns, and triggers
+ *          device functionality A
+ * Input 2: maps a device's BARs, sets up one DMA pattern, and triggers device
+ *          functionality B
+ *
+ * This function attempts to produce an input that:
+ * Ouptut: maps a device's BARs, set up three DMA patterns, triggers
+ *          functionality A device, replaces the DMA patterns with a single
+ *          patten, and triggers device functionality B.
+ */
+static size_t generic_fuzz_crossover(const uint8_t *data1, size_t size1, const
+                                     uint8_t *data2, size_t size2, uint8_t *out,
+                                     size_t max_out_size, unsigned int seed)
+{
+    size_t copy_len = 0, size = 0;
+
+    /* Check that we have enough space for data1 and at least part of data2 */
+    if (max_out_size <= size1 + strlen(SEPARATOR) * 3 + 2) {
+        return 0;
+    }
+
+    /* Copy_Len in the first input */
+    copy_len = size1;
+    memcpy(out + size, data1, copy_len);
+    size += copy_len;
+    max_out_size -= copy_len;
+
+    /* Append a separator */
+    copy_len = strlen(SEPARATOR);
+    memcpy(out + size, SEPARATOR, copy_len);
+    size += copy_len;
+    max_out_size -= copy_len;
+
+    /* Clear out the DMA Patterns */
+    copy_len = 1;
+    if (copy_len) {
+        out[size] = OP_CLEAR_DMA_PATTERNS;
+    }
+    size += copy_len;
+    max_out_size -= copy_len;
+
+    /* Append a separator */
+    copy_len = strlen(SEPARATOR);
+    memcpy(out + size, SEPARATOR, copy_len);
+    size += copy_len;
+    max_out_size -= copy_len;
+
+    /* Disable PCI ops. Assume data1 took care of setting up PCI */
+    copy_len = 1;
+    if (copy_len) {
+        out[size] = OP_DISABLE_PCI;
+    }
+    size += copy_len;
+    max_out_size -= copy_len;
+
+    /* Append a separator */
+    copy_len = strlen(SEPARATOR);
+    memcpy(out + size, SEPARATOR, copy_len);
+    size += copy_len;
+    max_out_size -= copy_len;
+
+    /* Copy_Len over the second input */
+    copy_len = MIN(size2, max_out_size);
+    memcpy(out + size, data2, copy_len);
+    size += copy_len;
+    max_out_size -= copy_len;
+
+    return  size;
+}
+
+
+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 GString *generic_fuzz_predefined_config_cmdline(FuzzTarget *t)
+{
+    gchar *args;
+    const generic_fuzz_config *config;
+    g_assert(t->opaque);
+
+    config = t->opaque;
+    setenv("QEMU_AVOID_DOUBLE_FETCH", "1", 1);
+    if (config->argfunc) {
+        args = config->argfunc();
+        setenv("QEMU_FUZZ_ARGS", args, 1);
+        g_free(args);
+    } else {
+        g_assert_nonnull(config->args);
+        setenv("QEMU_FUZZ_ARGS", config->args, 1);
+    }
+    setenv("QEMU_FUZZ_OBJECTS", config->objects, 1);
+    return generic_fuzz_cmdline(t);
+}
+
+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,
+            .crossover = generic_fuzz_crossover
+    });
+
+    GString *name;
+    const generic_fuzz_config *config;
+
+    for (int i = 0;
+         i < sizeof(predefined_configs) / sizeof(generic_fuzz_config);
+         i++) {
+        config = predefined_configs + i;
+        name = g_string_new("generic-fuzz");
+        g_string_append_printf(name, "-%s", config->name);
+        fuzz_add_target(&(FuzzTarget){
+                .name = name->str,
+                .description = "Predefined generic-fuzz config.",
+                .get_init_cmdline = generic_fuzz_predefined_config_cmdline,
+                .pre_fuzz = generic_pre_fuzz,
+                .fuzz = generic_fuzz,
+                .crossover = generic_fuzz_crossover,
+                .opaque = (void *)config
+        });
+    }
+}
+
+fuzz_target_init(register_generic_fuzz_targets);