qemu

generic_fuzz.c (31740B)

---

 /*
  * 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/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 fuzz_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
          *  fuzz_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 = fuzz_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)
 {
     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) {
             /*
              * 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;
     g_setenv("QEMU_AVOID_DOUBLE_FETCH", "1", 1);
     if (config->argfunc) {
         args = config->argfunc();
         g_setenv("QEMU_FUZZ_ARGS", args, 1);
         g_free(args);
     } else {
         g_assert_nonnull(config->args);
         g_setenv("QEMU_FUZZ_ARGS", config->args, 1);
     }
     g_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);