[PATCH v2 02/15] fuzz: Add general virtual-device fuzzer

[Alexander Bulekov]

This is a generic fuzzer designed to fuzz a virtual device's
MemoryRegions, as long as they exist within the Memory or Port IO (if it
exists) AddressSpaces. The fuzzer's input is interpreted into a sequence
of qtest commands (outb, readw, etc). The interpreted commands are
separated by a magic seaparator, which should be easy for the fuzzer to
guess. Without ASan, the separator can be specified as a "dictionary
value" using the -dict argument (see libFuzzer documentation).

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
 tests/qtest/fuzz/Makefile.include |   1 +
 tests/qtest/fuzz/general_fuzz.c   | 494 ++++++++++++++++++++++++++++++
 2 files changed, 495 insertions(+)
 create mode 100644 tests/qtest/fuzz/general_fuzz.c

diff --git a/tests/qtest/fuzz/Makefile.include 
b/tests/qtest/fuzz/Makefile.include
index 5bde793bf2..854322efb6 100644
--- a/tests/qtest/fuzz/Makefile.include
+++ b/tests/qtest/fuzz/Makefile.include
@@ -11,6 +11,7 @@ fuzz-obj-y += tests/qtest/fuzz/qtest_wrappers.o
 fuzz-obj-$(CONFIG_PCI_I440FX) += tests/qtest/fuzz/i440fx_fuzz.o
 fuzz-obj-$(CONFIG_VIRTIO_NET) += tests/qtest/fuzz/virtio_net_fuzz.o
 fuzz-obj-$(CONFIG_SCSI) += tests/qtest/fuzz/virtio_scsi_fuzz.o
+fuzz-obj-y += tests/qtest/fuzz/general_fuzz.o
 
 FUZZ_CFLAGS += -I$(SRC_PATH)/tests -I$(SRC_PATH)/tests/qtest
 
diff --git a/tests/qtest/fuzz/general_fuzz.c b/tests/qtest/fuzz/general_fuzz.c
new file mode 100644
index 0000000000..01bcb029b1
--- /dev/null
+++ b/tests/qtest/fuzz/general_fuzz.c
@@ -0,0 +1,494 @@
+/*
+ * General 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 "cpu.h"
+#include "tests/qtest/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 100000000
+
+typedef struct {
+    size_t addr;
+    size_t len; /* The number of bytes until the end of the I/O region */
+} address_range;
+
+static useconds_t timeout = 100000;
+/*
+ * List of memory regions that are children of QOM objects specified by the
+ * user for fuzzing.
+ */
+static GPtrArray *fuzzable_memoryregions;
+/*
+ * 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,
+                                    MemoryRegion *io_space,
+                                    uint8_t index,
+                                    uint32_t offset) {
+    MemoryRegion *mr, *root;
+    index = index % fuzzable_memoryregions->len;
+    int candidate_regions = 0;
+    int i = 0;
+    int ind = index;
+    size_t abs_addr;
+    AddressSpace *as = (io_space == get_system_memory()) ? 
&address_space_memory : &address_space_io;
+
+    while (ind >= 0 && fuzzable_memoryregions->len) {
+        *result = (address_range){0, 0};
+        mr = g_ptr_array_index(fuzzable_memoryregions, i);
+        if (mr->enabled) {
+            abs_addr = mr->addr;
+            for (root = mr; root->container; ) {
+                root = root->container;
+                abs_addr += root->addr;
+            }
+            /*
+             * Only consider the region if it is rooted at the io_space we want
+             */
+            if (root == io_space) {
+                hwaddr xlat, len;
+                if(address_space_translate(as, abs_addr, &xlat, &len, true, 
MEMTXATTRS_UNSPECIFIED) == mr){
+                    ind--;
+                    candidate_regions++;
+                    result->addr = abs_addr;
+                    if(mr->size){
+                        result->addr += (offset % mr->size);
+                    }
+                    result->len = mr->size-(result->addr-abs_addr);
+                }
+            }
+        }
+        ++i;
+        /* Loop around */
+        if (i == fuzzable_memoryregions->len) {
+            /* No enabled regions in our io_space? */
+            if (candidate_regions == 0) {
+                break;
+            }
+            i = 0;
+        }
+    }
+    return candidate_regions != 0;
+}
+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 success = get_io_address(result, get_system_io(), index, offset);
+    return success && result->addr <= 0xFFFF;
+}
+static bool get_mmio_address(address_range *result,
+                                      uint8_t index, uint32_t offset)
+{
+    return get_io_address(result, get_system_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.len >= 2) {
+            qtest_inw(s, abs.addr);
+        }
+        break;
+    case Long:
+        if (abs.len >= 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.len >= 2) {
+            qtest_outw(s, abs.addr, a.value & 0xFFFF);
+        }
+        break;
+    case Long:
+        if (abs.len >= 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.len >= 2) {
+            qtest_readw(s, abs.addr);
+        }
+        break;
+    case Long:
+        if (abs.len >= 4) {
+            qtest_readl(s, abs.addr);
+        }
+        break;
+    case Quad:
+        if (abs.len >= 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.len >= 2) {
+            qtest_writew(s, abs.addr, a.value & 0xFFFF);
+        }
+        break;
+    case Long:
+        if (abs.len >= 4) {
+            qtest_writel(s, abs.addr, a.value & 0xFFFFFFFF);
+        }
+        break;
+    case Quad:
+        if (abs.len >= 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 (getenv("QTEST_LOG")) {
+        fprintf(stderr, "[Timeout]\n");
+        fflush(stderr);
+    }
+    _Exit(0);
+}
+
+/*
+ * Here, we interpret random bytes from the fuzzer, as a sequence of commands.
+ * Our commands are variable-width, so we use a separator, SEPARATOR, to 
specify
+ * the boundaries between commands. This is just a random 32-bit value, which
+ * is easily identified by libfuzzer+AddressSanitizer, as long as we use
+ * memmem. It can also be included in the fuzzer's dictionary. More details
+ * here:
+ * https://github.com/google/fuzzing/blob/master/docs/split-inputs.md
+ *
+ * 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 general_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) ||
+            memory_region_is_romd(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_ptr_array_remove_fast(fuzzable_memoryregions, mr);
+            g_ptr_array_add(fuzzable_memoryregions, mr);
+        }
+    }
+    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) ||
+                 memory_region_is_romd(mr)) == false) {
+                g_ptr_array_remove_fast(fuzzable_memoryregions, mr);
+                g_ptr_array_add(fuzzable_memoryregions, mr);
+            }
+        }
+    }
+    return 0;
+}
+
+static void general_pre_fuzz(QTestState *s)
+{
+    if (!getenv("QEMU_FUZZ_OBJECTS")) {
+        usage();
+    }
+    if (getenv("QEMU_FUZZ_TIMEOUT")) {
+        timeout = g_ascii_strtoll(getenv("QEMU_FUZZ_TIMEOUT"), NULL, 0);
+    }
+
+    fuzzable_memoryregions = g_ptr_array_new();
+    char **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");
+    for (int i = 0; i < fuzzable_memoryregions->len; i++) {
+        MemoryRegion *mr;
+        mr = g_ptr_array_index(fuzzable_memoryregions, i);
+        printf("  * %s (size %lx)\n",
+               object_get_canonical_path_component(&(mr->parent_obj)),
+               mr->addr);
+    }
+
+    if(!fuzzable_memoryregions->len){
+        printf("No fuzzable memory regions found...\n");
+        exit(0);
+    }
+
+    counter_shm_init();
+}
+static GString *general_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 64 %s ", getenv("QEMU_FUZZ_ARGS"));
+    return cmd_line;
+}
+
+static void register_general_fuzz_targets(void)
+{
+    fuzz_add_target(&(FuzzTarget){
+            .name = "general-fuzz",
+            .description = "Fuzz based on any qemu command-line args. ",
+            .get_init_cmdline = general_fuzz_cmdline,
+            .pre_fuzz = general_pre_fuzz,
+            .fuzz = general_fuzz});
+}
+
+fuzz_target_init(register_general_fuzz_targets);
-- 
2.27.0