[PATCH 00/12] Add a General Virtual Device Fuzzer

[PATCH 00/12] Add a General Virtual Device Fuzzer

[Alexander Bulekov]

This is a general virtual-device fuzzer, designed to fuzz devices over Port IO,
MMIO, and DMA.
To get started with this:
 1. Build the fuzzers (see docs/devel/fuzzing.txt)
    Note: Build with --enable-sanitizers, or create a "dictionary file":
    echo kw1=\"\x84\x05\x5C\x5E\" > dict
    and pass it as an argument to libFuzzer with -dict=./dict
    This magic value is a command separator that lets the fuzzer perform
    multiple IO actions with a single input.

 2. Pick the qemu arguments you wish to fuzz:
    export QEMU_FUZZ_ARGS="-M q35 -device virtio-balloon"

 3. Tell the fuzzer which QOM objects or MemoryRegion names to fuzz. I find the
 "info qom-tree", "info qtree" and "info mtree" commands useful for identifying
 these. Supports globbing. Here I will try to simultaneously fuzz(for no good
 reason) virtio-balloon and e1000e, which is included by default in the q35:
    export QEMU_FUZZ_OBJECTS='virtio* e1000*'
    You can also try to fuzz the whole machine:
    export QEMU_FUZZ_OBJECTS='*'

 4. Run the fuzzer for 0 inputs. The fuzzer should output a list of
 MemoryRegions/PCI Devices it will try to fuzz. Confirm that these match your
 expectations.
    ./i386-softmmu/qemu-fuzz-i386 --fuzz-target=general-fuzz -runs=0

 5. Run the fuzzer:
    ./i386-softmmu/qemu-fuzz-i386 --fuzz-target=general-fuzz 


Basically, at the core, this fuzzer is an interpreter that splits the input
into a series of commands, such as mmio_write, pio_write, etc. We structure
these commands to hit only MemoryRegions that are associated with the devices
specified in QEMU_FUZZ_OBJECTS. Additionally, these patches add "hooks" to
functions that are typically used by virtual-devices to read from RAM (DMA).
These hooks attempt to populate these DMA regions with fuzzed data, just in
time.

Patch 1 changes the way we tell QTest to log to stderr (becomes important when
building reproducers with this fuzzer)

Patches 2-6 add the fuzzer and the necessary DMA callbacks

Patches 7-10 are my (very rough) attempt at integrating this into OSS-Fuzz

Patches 11-12 contain the "reordering" and minimization scripts used to
produce a QTest reproducer for a crash.

Additional notes:
 * With the latest changes, the
 fuzzer is quite effective at only targeting the device we care about,
 so it will probably be beneficial to allow reboot() as an option for
 resetting state, rather than fork(), for devices where that works well.

 * We have only scratched the surface for device "backends". I.e. I am using
 fake null-co:// drives for block devices and SLiRP for network devices (see
 scripts/oss-fuzz/general_fuzzer_configs.yml). Using more complex backends will
 likely break due to forking/threading/statefulness related reasons and will
 require more work.

* Because I still can't figure out how to make QOS do what I want, this
  only maps PCI BARs on i386. For other targets, the fuzzer can still
  try to do it on its own :). Only did a very simple test on ppc and arm

 * This is failing on GitLab due to a leak:
 https://gitlab.com/a1xndr/qemu/-/jobs/652179729
 I am not sure how to work around it yet, since I don't think we can
 free what the trace says we should free (argv from wordexp that we pass
 to qemu_main).


Some of the issues I have found or reproduced with this fuzzer:
https://bugs.launchpad.net/bugs/1525123
https://bugs.launchpad.net/bugs/1681439
https://bugs.launchpad.net/bugs/1777315
https://bugs.launchpad.net/bugs/1878034
https://bugs.launchpad.net/bugs/1878043
https://bugs.launchpad.net/bugs/1878054
https://bugs.launchpad.net/bugs/1878057
https://bugs.launchpad.net/bugs/1878067
https://bugs.launchpad.net/bugs/1878134
https://bugs.launchpad.net/bugs/1878136
https://bugs.launchpad.net/bugs/1878253
https://bugs.launchpad.net/bugs/1878255
https://bugs.launchpad.net/bugs/1878259
https://bugs.launchpad.net/bugs/1878263
https://bugs.launchpad.net/bugs/1878323
https://bugs.launchpad.net/bugs/1878641
https://bugs.launchpad.net/bugs/1878642
https://bugs.launchpad.net/bugs/1878645
https://bugs.launchpad.net/bugs/1878651
https://bugs.launchpad.net/bugs/1879223
https://bugs.launchpad.net/bugs/1879227
https://bugs.launchpad.net/bugs/1879531
https://bugs.launchpad.net/bugs/1880355
https://bugs.launchpad.net/bugs/1880539
https://bugs.launchpad.net/bugs/1884693
https://bugs.launchpad.net/bugs/1886362
https://bugs.launchpad.net/bugs/1887303
https://bugs.launchpad.net/bugs/1887309
https://bugs.launchpad.net/bugs/697510

-Alex

Alexander Bulekov (12):
  fuzz: Change the way we write qtest log to stderr
  fuzz: Add general virtual-device fuzzer
  fuzz: Add PCI features to the general fuzzer
  fuzz: Add DMA support to the generic-fuzzer
  fuzz: Declare DMA Read callback function
  fuzz: Add fuzzer callbacks to DMA-read functions
  scripts/oss-fuzz: Add wrapper program for generic fuzzer
  scripts/oss-fuzz: Add general-fuzzer build script
  scripts/oss-fuzz: Add general-fuzzer configs for oss-fuzz
  scripts/oss-fuzz: build the general-fuzzer configs
  scripts/oss-fuzz: Add script to reorder a general-fuzzer trace
  scripts/oss-fuzz: Add crash trace minimization script

 exec.c                                        |   2 +
 include/exec/memory.h                         |  16 +
 include/exec/memory_ldst_cached.inc.h         |   3 +
 memory_ldst.inc.c                             |   4 +
 scripts/oss-fuzz/build.sh                     |   8 +-
 scripts/oss-fuzz/build_general_fuzzers.py     |  62 ++
 scripts/oss-fuzz/general_fuzzer_configs.yml   | 103 +++
 scripts/oss-fuzz/minimize_qtest_trace.py      | 117 +++
 .../oss-fuzz/reorder_fuzzer_qtest_trace.py    |  94 +++
 scripts/oss-fuzz/target.c                     |  40 +
 softmmu/memory.c                              |  14 +
 tests/qtest/fuzz/Makefile.include             |   1 +
 tests/qtest/fuzz/fuzz.c                       |   5 +-
 tests/qtest/fuzz/general_fuzz.c               | 758 ++++++++++++++++++
 14 files changed, 1223 insertions(+), 4 deletions(-)
 create mode 100755 scripts/oss-fuzz/build_general_fuzzers.py
 create mode 100644 scripts/oss-fuzz/general_fuzzer_configs.yml
 create mode 100755 scripts/oss-fuzz/minimize_qtest_trace.py
 create mode 100755 scripts/oss-fuzz/reorder_fuzzer_qtest_trace.py
 create mode 100644 scripts/oss-fuzz/target.c
 create mode 100644 tests/qtest/fuzz/general_fuzz.c

-- 
2.27.0

[PATCH 01/12] fuzz: Change the way we write qtest log to stderr

[Alexander Bulekov]

Telling QTest to log to /dev/fd/2, essentially results in dup(2). This
is fine, if other code isn't logging to stderr. Otherwise, the order of
the logs is mixed due to buffering issues, since two file-descriptors
are used to write to the same file. We can avoid this, since just
specifying "-qtest" sets the log fd to stderr. If we want to disable
qtest logs, we can just add -qtest-log none.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
 tests/qtest/fuzz/fuzz.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/tests/qtest/fuzz/fuzz.c b/tests/qtest/fuzz/fuzz.c
index 031594a686..8234b68754 100644
--- a/tests/qtest/fuzz/fuzz.c
+++ b/tests/qtest/fuzz/fuzz.c
@@ -202,9 +202,8 @@ int LLVMFuzzerInitialize(int *argc, char ***argv, char ***envp)
 
     /* Run QEMU's softmmu main with the fuzz-target dependent arguments */
     GString *cmd_line = fuzz_target->get_init_cmdline(fuzz_target);
-    g_string_append_printf(cmd_line,
-                           " -qtest /dev/null -qtest-log %s",
-                           getenv("QTEST_LOG") ? "/dev/fd/2" : "/dev/null");
+    g_string_append_printf(cmd_line, " %s -qtest /dev/null ",
+                           getenv("QTEST_LOG") ? "" : "-qtest-log none");
 
     /* Split the runcmd into an argv and argc */
     wordexp_t result;
-- 
2.27.0

[PATCH 02/12] 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   | 467 ++++++++++++++++++++++++++++++
 2 files changed, 468 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..fd92cc5bdf
--- /dev/null
+++ b/tests/qtest/fuzz/general_fuzz.c
@@ -0,0 +1,467 @@
+/*
+ * 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"
+
+/*
+ * CMD_SEP is a random 32-bit value used to separate "commands" in the fuzz
+ * input
+ */
+#define CMD_SEP "\x84\x05\x5C\x5E"
+#define DEFAULT_TIMEOUT_US 100000
+
+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;
+
+    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) {
+                ind--;
+                candidate_regions++;
+                result->addr = abs_addr + (offset % mr->size);
+                result->len = mr->size - (offset % mr->size);
+            }
+        }
+        ++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, CMD_SEP, 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 CMD_SEP 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_out,
+        op_read,
+        op_write,
+        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;
+            sigemptyset(&sact.sa_mask);
+            sact.sa_flags = 0;
+            sact.sa_handler = handle_timeout;
+            sigaction(SIGALRM, &sact, NULL);
+            ualarm(timeout, 0);
+        }
+
+        while (cmd && Size) {
+            /* Get the length until the next command or end of input */
+            nextcmd = memmem(cmd, Size, CMD_SEP, strlen(CMD_SEP));
+            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(CMD_SEP) - 1 : nextcmd;
+            Size = Size - (cmd_len + sizeof(CMD_SEP) - 1);
+        }
+        _Exit(0);
+    } else {
+        flush_events(s);
+        wait(NULL);
+    }
+}
+
+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))) {
+        printf("Matched Object by Type: %s\n", 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();
+    wordexp_t result;
+    wordexp(getenv("QEMU_FUZZ_OBJECTS"), &result, 0);
+    for (int i = 0; i < result.we_wordc; i++) {
+        object_child_foreach_recursive(qdev_get_machine(),
+                                    locate_fuzz_objects,
+                                    result.we_wordv[i]);
+    }
+
+    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);
+    }
+    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

[PATCH 03/12] fuzz: Add PCI features to the general fuzzer

[Alexander Bulekov]

This patch compares TYPE_PCI_DEVICE objects against the user-provided
matching pattern. If there is a match, we use some hacks and leverage
QOS to map each possible BAR for that device. Now fuzzed inputs might be
converted to pci_read/write commands which target specific. This means
that we can fuzz a particular device's PCI configuration space,

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
 tests/qtest/fuzz/general_fuzz.c | 114 ++++++++++++++++++++++++++++++++
 1 file changed, 114 insertions(+)

diff --git a/tests/qtest/fuzz/general_fuzz.c b/tests/qtest/fuzz/general_fuzz.c
index fd92cc5bdf..e715b77d59 100644
--- a/tests/qtest/fuzz/general_fuzz.c
+++ b/tests/qtest/fuzz/general_fuzz.c
@@ -24,6 +24,9 @@
 #include "exec/ramblock.h"
 #include "exec/address-spaces.h"
 #include "hw/qdev-core.h"
+#include "tests/qtest/libqos/pci.h"
+#include "tests/qtest/libqos/pci-pc.h"
+#include "hw/pci/pci.h"
 
 /*
  * CMD_SEP is a random 32-bit value used to separate "commands" in the fuzz
@@ -32,6 +35,9 @@
 #define CMD_SEP "\x84\x05\x5C\x5E"
 #define DEFAULT_TIMEOUT_US 100000
 
+#define PCI_HOST_BRIDGE_CFG 0xcf8
+#define PCI_HOST_BRIDGE_DATA 0xcfc
+
 typedef struct {
     size_t addr;
     size_t len; /* The number of bytes until the end of the I/O region */
@@ -43,6 +49,8 @@ static useconds_t timeout = 100000;
  * user for fuzzing.
  */
 static GPtrArray *fuzzable_memoryregions;
+static GPtrArray *fuzzable_pci_devices;
+
 /*
  * 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
@@ -267,6 +275,65 @@ static void op_write(QTestState *s, const unsigned char * data, size_t len)
         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) {
+        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) {
+        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_clock_step(QTestState *s, const unsigned char *data, size_t len)
 {
     qtest_clock_step_next(s);
@@ -311,6 +378,8 @@ static void general_fuzz(QTestState *s, const unsigned char *Data, size_t Size)
         op_out,
         op_read,
         op_write,
+        op_pci_read,
+        op_pci_write,
         op_clock_step,
     };
     const unsigned char *cmd = Data;
@@ -397,6 +466,19 @@ static int locate_fuzz_objects(Object *child, void *opaque)
         printf("Matched Object by Type: %s\n", object_get_typename(child));
         /* 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)) {
         if (g_pattern_match_simple(pattern,
             object_get_canonical_path_component(child))) {
@@ -416,6 +498,7 @@ static int locate_fuzz_objects(Object *child, void *opaque)
 
 static void general_pre_fuzz(QTestState *s)
 {
+    QPCIBus *qpci_bus;
     if (!getenv("QEMU_FUZZ_OBJECTS")) {
         usage();
     }
@@ -424,6 +507,7 @@ static void general_pre_fuzz(QTestState *s)
     }
 
     fuzzable_memoryregions = g_ptr_array_new();
+    fuzzable_pci_devices = g_ptr_array_new();
     wordexp_t result;
     wordexp(getenv("QEMU_FUZZ_OBJECTS"), &result, 0);
     for (int i = 0; i < result.we_wordc; i++) {
@@ -440,6 +524,36 @@ static void general_pre_fuzz(QTestState *s)
                object_get_canonical_path_component(&(mr->parent_obj)),
                mr->addr);
     }
+
+#ifdef TARGET_I386
+    printf("\n.. and the following Devices in the PCI Configuration Space:\n");
+    if (fuzzable_pci_devices->len) {
+        /*
+         * qpci_new_pc can't be used for non x86... What else can we do? Map
+         * BARs, without QOS?
+         */
+        qpci_bus = qpci_new_pc(s, NULL);
+        for (int i = 0; i < fuzzable_pci_devices->len; i++) {
+            PCIDevice *dev;
+            QPCIDevice *qdev;
+            dev = g_ptr_array_index(fuzzable_pci_devices, i);
+            qdev = qpci_device_find(qpci_bus, dev->devfn);
+            for (int j = 0; j < 5; j++) {
+                if (dev->io_regions[j].size) {
+                    qpci_iomap(qdev, j, NULL);
+                }
+            }
+            qpci_device_enable(qdev);
+            g_free(qdev);
+            printf("  * %x:%x device: %x function: %x)\n",
+                    pci_get_word(dev->config + PCI_VENDOR_ID),
+                    pci_get_word(dev->config + PCI_DEVICE_ID),
+                    PCI_SLOT(dev->devfn),
+                    PCI_FUNC(dev->devfn));
+        }
+        qpci_free_pc(qpci_bus);
+    }
+#endif
     counter_shm_init();
 }
 static GString *general_fuzz_cmdline(FuzzTarget *t)
-- 
2.27.0

[PATCH 04/12] fuzz: Add DMA support to the generic-fuzzer

[Alexander Bulekov]

When a virtual-device tries to access some buffer in memory over DMA, we
add call-backs into the fuzzer(next commit). The fuzzer checks verifies
that the DMA request maps to a physical RAM address and fills the memory
with fuzzer-provided data. The patterns that we use to fill this memory
are specified using add_dma_pattern and clear_dma_patterns operations.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
 tests/qtest/fuzz/general_fuzz.c | 177 ++++++++++++++++++++++++++++++++
 1 file changed, 177 insertions(+)

diff --git a/tests/qtest/fuzz/general_fuzz.c b/tests/qtest/fuzz/general_fuzz.c
index e715b77d59..4b6967c5d2 100644
--- a/tests/qtest/fuzz/general_fuzz.c
+++ b/tests/qtest/fuzz/general_fuzz.c
@@ -27,6 +27,7 @@
 #include "tests/qtest/libqos/pci.h"
 #include "tests/qtest/libqos/pci-pc.h"
 #include "hw/pci/pci.h"
+#include "hw/boards.h"
 
 /*
  * CMD_SEP is a random 32-bit value used to separate "commands" in the fuzz
@@ -34,6 +35,7 @@
  */
 #define CMD_SEP "\x84\x05\x5C\x5E"
 #define DEFAULT_TIMEOUT_US 100000
+#define MAX_DMA_FILL_SIZE 0x10000
 
 #define PCI_HOST_BRIDGE_CFG 0xcf8
 #define PCI_HOST_BRIDGE_DATA 0xcfc
@@ -44,6 +46,24 @@ typedef struct {
 } address_range;
 
 static useconds_t timeout = 100000;
+/*
+ * 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 03   00 05 03   00 07 03 ...
+ */
+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.
@@ -51,6 +71,122 @@ static useconds_t timeout = 100000;
 static GPtrArray *fuzzable_memoryregions;
 static GPtrArray *fuzzable_pci_devices;
 
+/*
+ * 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;
+int dma_pattern_index;
+
+/*
+ * 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;
+}
+
+/*
+ * 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
+ * general_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, bool is_write)
+{
+    /* Are we in the general-fuzzer or are we using another fuzz-target? */
+    if (!qts_global) {
+        return;
+    }
+
+    /*
+     * If the device is trying to read from a ROM, exit early. We do not want
+     * to fuzz devices using data that we have no control over.
+     */
+    if (mr->readonly) {
+        _Exit(0);
+    }
+
+    /*
+     * 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 is not a read (what happens for a address_space_map
+     *   with is_write=True? Can the device use the same pointer to do reads?)
+     * - The DMA request hits past the bounds of our RAM
+     */
+    if (dma_patterns->len == 0
+        || len == 0
+        || mr != MACHINE(qdev_get_machine())->ram
+        || is_write
+        || addr > current_machine->ram_size) {
+        return;
+    }
+
+    /*
+     * If we overlap with any existing dma_regions, split the range and only
+     * populate the non-overlapping parts.
+     */
+    for (int i = 0; i < dma_regions->len && !avoid_double_fetches; ++i) {
+        address_range region = g_array_index(dma_regions, address_range, i);
+        if (addr < region.addr + region.len && addr + len > region.addr) {
+            if (addr < region.addr) {
+                fuzz_dma_read_cb(addr, region.addr - addr, mr, is_write);
+            }
+            if (addr + len > region.addr + region.len) {
+                fuzz_dma_read_cb(region.addr + region.len,
+                        addr + len - (region.addr + region.len), mr, is_write);
+            }
+            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 = pattern_alloc(p, ar.len);
+    if (getenv("QTEST_LOG")) {
+        /*
+         * 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] ");
+        fflush(stderr);
+        qtest_memwrite(qts_global, ar.addr, buf, ar.len);
+    } else {
+       /*
+        * Populate the region using address_space_write_rom to avoid writing to
+        * any IO MemoryRegions
+        */
+        address_space_write_rom(first_cpu->as, ar.addr, MEMTXATTRS_UNSPECIFIED,
+                buf, ar.len);
+    }
+    free(buf);
+
+    /* 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
@@ -334,6 +470,35 @@ static void op_pci_write(QTestState *s, const unsigned char * data, size_t len)
     }
 }
 
+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);
@@ -380,6 +545,8 @@ static void general_fuzz(QTestState *s, const unsigned char *Data, size_t Size)
         op_write,
         op_pci_read,
         op_pci_write,
+        op_add_dma_pattern,
+        op_clear_dma_patterns,
         op_clock_step,
     };
     const unsigned char *cmd = Data;
@@ -433,6 +600,9 @@ static void usage(void)
     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);
@@ -502,9 +672,16 @@ static void general_pre_fuzz(QTestState *s)
     if (!getenv("QEMU_FUZZ_OBJECTS")) {
         usage();
     }
+    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;
+
+    dma_regions = g_array_new(false, false, sizeof(address_range));
+    dma_patterns = g_array_new(false, false, sizeof(pattern));
 
     fuzzable_memoryregions = g_ptr_array_new();
     fuzzable_pci_devices = g_ptr_array_new();
-- 
2.27.0

[PATCH 05/12] fuzz: Declare DMA Read callback function

[Alexander Bulekov]

This patch declares the fuzz_dma_read_cb function and uses the
preprocessor and linker(weak symbols) to handle these cases:

When we build softmmu/all with --enable-fuzzing, there should be no
strong symbol defined for fuzz_dma_read_cb, and we link against a weak
stub function.

When we build softmmu/fuzz with --enable-fuzzing, we link agains the
strong symbol in general_fuzz.c

When we build softmmu/all without --enable-fuzzing, fuzz_dma_read_cb is
an empty, inlined function. As long as we don't call any other functions
when building the arguments, there should be no overhead.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
 include/exec/memory.h | 15 +++++++++++++++
 softmmu/memory.c      | 13 +++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/include/exec/memory.h b/include/exec/memory.h
index 307e527835..2ec3b597f1 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -47,6 +47,21 @@
         OBJECT_GET_CLASS(IOMMUMemoryRegionClass, (obj), \
                          TYPE_IOMMU_MEMORY_REGION)
 
+#ifdef CONFIG_FUZZ
+void fuzz_dma_read_cb(size_t addr,
+                      size_t len,
+                      MemoryRegion *mr,
+                      bool is_write);
+#else
+static inline void fuzz_dma_read_cb(size_t addr,
+                                    size_t len,
+                                    MemoryRegion *mr,
+                                    bool is_write)
+{
+    /* Do Nothing */
+}
+#endif
+
 extern bool global_dirty_log;
 
 typedef struct MemoryRegionOps MemoryRegionOps;
diff --git a/softmmu/memory.c b/softmmu/memory.c
index af25987518..b0c2cf2535 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -3223,6 +3223,19 @@ void memory_region_init_rom_device(MemoryRegion *mr,
     vmstate_register_ram(mr, owner_dev);
 }
 
+/*
+ * Support softmmu builds with CONFIG_FUZZ using a weak symbol and a stub for
+ * the fuzz_dma_read_cb callback
+ */
+#ifdef CONFIG_FUZZ
+void __attribute__((weak)) fuzz_dma_read_cb(size_t addr,
+                      size_t len,
+                      MemoryRegion *mr,
+                      bool is_write)
+{
+}
+#endif
+
 static const TypeInfo memory_region_info = {
     .parent             = TYPE_OBJECT,
     .name               = TYPE_MEMORY_REGION,
-- 
2.27.0

[PATCH 06/12] fuzz: Add fuzzer callbacks to DMA-read functions

[Alexander Bulekov]

We should be careful to not call any functions besides fuzz_dma_read_cb.
Without --enable-fuzzing, fuzz_dma_read_cb is an empty inlined function.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
I'd appreciate another set of eyes on this. Basically, we only care about
DMA reads to RAM. This is why I assume stuff like "addr" or "cache->xlat
+ addr" is an absolute address.

 exec.c                                | 2 ++
 include/exec/memory.h                 | 1 +
 include/exec/memory_ldst_cached.inc.h | 3 +++
 memory_ldst.inc.c                     | 4 ++++
 softmmu/memory.c                      | 1 +
 5 files changed, 11 insertions(+)

diff --git a/exec.c b/exec.c
index 6f381f98e2..c81f41514d 100644
--- a/exec.c
+++ b/exec.c
@@ -3241,6 +3241,7 @@ MemTxResult flatview_read_continue(FlatView *fv, hwaddr addr,
             stn_he_p(buf, l, val);
         } else {
             /* RAM case */
+            fuzz_dma_read_cb(addr, len, mr, false);
             ram_ptr = qemu_ram_ptr_length(mr->ram_block, addr1, &l, false);
             memcpy(buf, ram_ptr, l);
         }
@@ -3601,6 +3602,7 @@ void *address_space_map(AddressSpace *as,
     memory_region_ref(mr);
     *plen = flatview_extend_translation(fv, addr, len, mr, xlat,
                                         l, is_write, attrs);
+    fuzz_dma_read_cb(addr, *plen, mr, is_write);
     ptr = qemu_ram_ptr_length(mr->ram_block, xlat, plen, true);
 
     return ptr;
diff --git a/include/exec/memory.h b/include/exec/memory.h
index 2ec3b597f1..f8b943521a 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -2444,6 +2444,7 @@ address_space_read_cached(MemoryRegionCache *cache, hwaddr addr,
                           void *buf, hwaddr len)
 {
     assert(addr < cache->len && len <= cache->len - addr);
+    fuzz_dma_read_cb(cache->xlat + addr, len, cache->mrs.mr, false);
     if (likely(cache->ptr)) {
         memcpy(buf, cache->ptr + addr, len);
         return MEMTX_OK;
diff --git a/include/exec/memory_ldst_cached.inc.h b/include/exec/memory_ldst_cached.inc.h
index fd4bbb40e7..aff574039f 100644
--- a/include/exec/memory_ldst_cached.inc.h
+++ b/include/exec/memory_ldst_cached.inc.h
@@ -28,6 +28,7 @@ static inline uint32_t ADDRESS_SPACE_LD_CACHED(l)(MemoryRegionCache *cache,
     hwaddr addr, MemTxAttrs attrs, MemTxResult *result)
 {
     assert(addr < cache->len && 4 <= cache->len - addr);
+    fuzz_dma_read_cb(cache->xlat + addr, 4, cache->mrs.mr, false);
     if (likely(cache->ptr)) {
         return LD_P(l)(cache->ptr + addr);
     } else {
@@ -39,6 +40,7 @@ static inline uint64_t ADDRESS_SPACE_LD_CACHED(q)(MemoryRegionCache *cache,
     hwaddr addr, MemTxAttrs attrs, MemTxResult *result)
 {
     assert(addr < cache->len && 8 <= cache->len - addr);
+    fuzz_dma_read_cb(cache->xlat + addr, 8, cache->mrs.mr, false);
     if (likely(cache->ptr)) {
         return LD_P(q)(cache->ptr + addr);
     } else {
@@ -50,6 +52,7 @@ static inline uint32_t ADDRESS_SPACE_LD_CACHED(uw)(MemoryRegionCache *cache,
     hwaddr addr, MemTxAttrs attrs, MemTxResult *result)
 {
     assert(addr < cache->len && 2 <= cache->len - addr);
+    fuzz_dma_read_cb(cache->xlat + addr, 2, cache->mrs.mr, false);
     if (likely(cache->ptr)) {
         return LD_P(uw)(cache->ptr + addr);
     } else {
diff --git a/memory_ldst.inc.c b/memory_ldst.inc.c
index c54aee4a95..8d45d2eeff 100644
--- a/memory_ldst.inc.c
+++ b/memory_ldst.inc.c
@@ -42,6 +42,7 @@ static inline uint32_t glue(address_space_ldl_internal, SUFFIX)(ARG1_DECL,
                                         MO_32 | devend_memop(endian), attrs);
     } else {
         /* RAM case */
+        fuzz_dma_read_cb(addr, 4, mr, false);
         ptr = qemu_map_ram_ptr(mr->ram_block, addr1);
         switch (endian) {
         case DEVICE_LITTLE_ENDIAN:
@@ -110,6 +111,7 @@ static inline uint64_t glue(address_space_ldq_internal, SUFFIX)(ARG1_DECL,
                                         MO_64 | devend_memop(endian), attrs);
     } else {
         /* RAM case */
+        fuzz_dma_read_cb(addr, 8, mr, false);
         ptr = qemu_map_ram_ptr(mr->ram_block, addr1);
         switch (endian) {
         case DEVICE_LITTLE_ENDIAN:
@@ -175,6 +177,7 @@ uint32_t glue(address_space_ldub, SUFFIX)(ARG1_DECL,
         r = memory_region_dispatch_read(mr, addr1, &val, MO_8, attrs);
     } else {
         /* RAM case */
+        fuzz_dma_read_cb(addr, 1, mr, false);
         ptr = qemu_map_ram_ptr(mr->ram_block, addr1);
         val = ldub_p(ptr);
         r = MEMTX_OK;
@@ -212,6 +215,7 @@ static inline uint32_t glue(address_space_lduw_internal, SUFFIX)(ARG1_DECL,
                                         MO_16 | devend_memop(endian), attrs);
     } else {
         /* RAM case */
+        fuzz_dma_read_cb(addr, 2, mr, false);
         ptr = qemu_map_ram_ptr(mr->ram_block, addr1);
         switch (endian) {
         case DEVICE_LITTLE_ENDIAN:
diff --git a/softmmu/memory.c b/softmmu/memory.c
index b0c2cf2535..be87044641 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -1405,6 +1405,7 @@ MemTxResult memory_region_dispatch_read(MemoryRegion *mr,
     unsigned size = memop_size(op);
     MemTxResult r;
 
+    fuzz_dma_read_cb(addr, size, mr, false);
     if (!memory_region_access_valid(mr, addr, size, false, attrs)) {
         *pval = unassigned_mem_read(mr, addr, size);
         return MEMTX_DECODE_ERROR;
-- 
2.27.0

[PATCH 07/12] scripts/oss-fuzz: Add wrapper program for generic fuzzer

[Alexander Bulekov]

On oss-fuzz we need some sort of wrapper to specify command-line
arguments or environment variables. When we had a similar problem with
other targets that I fixed with
05509c8e6d ("fuzz: select fuzz target using executable name")
by selecting the fuzz target based on the executable's name. In the
future should probably commit to one approach (wrapper binary or
argv0-based target selection).

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
 scripts/oss-fuzz/target.c | 40 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 scripts/oss-fuzz/target.c

diff --git a/scripts/oss-fuzz/target.c b/scripts/oss-fuzz/target.c
new file mode 100644
index 0000000000..4a7257412a
--- /dev/null
+++ b/scripts/oss-fuzz/target.c
@@ -0,0 +1,40 @@
+/*
+ * 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 <stdio.h>
+#include <stdlib.h>
+#include <limits.h>
+#include <libgen.h>
+#include <string.h>
+#include <unistd.h>
+
+
+/* Required for oss-fuzz to consider the binary a target. */
+static const char *magic __attribute__((used)) = "LLVMFuzzerTestOneInput";
+static const char args[] = {QEMU_FUZZ_ARGS, 0x00};
+static const char objects[] = {QEMU_FUZZ_OBJECTS, 0x00};
+
+int main(int argc, char *argv[])
+{
+    char path[PATH_MAX] = {0};
+    char *dir = dirname(argv[0]);
+    strncpy(path, dir, PATH_MAX);
+    strcat(path, "/deps/qemu-fuzz-i386-target-general-fuzz");
+
+    setenv("QEMU_FUZZ_ARGS", args, 0);
+    setenv("QEMU_FUZZ_OBJECTS", objects, 0);
+
+    argv[0] = path;
+    int ret = execvp(path, argv);
+    if (ret) {
+        perror("execv");
+    }
+    return ret;
+}
-- 
2.27.0

[PATCH 08/12] scripts/oss-fuzz: Add general-fuzzer build script

[Alexander Bulekov]

This parses a yaml file containing general-fuzzer configs and builds a
separate oss-fuzz wrapper binary for each one, changing some
preprocessor macros for each configuration. To avoid dealing with
escaping and stringifying, convert each string into a byte-array
representation

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
 scripts/oss-fuzz/build_general_fuzzers.py | 62 +++++++++++++++++++++++
 1 file changed, 62 insertions(+)
 create mode 100755 scripts/oss-fuzz/build_general_fuzzers.py

diff --git a/scripts/oss-fuzz/build_general_fuzzers.py b/scripts/oss-fuzz/build_general_fuzzers.py
new file mode 100755
index 0000000000..79f4664117
--- /dev/null
+++ b/scripts/oss-fuzz/build_general_fuzzers.py
@@ -0,0 +1,62 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+"""
+This script creates wrapper binaries that invoke the general-device-fuzzer with
+configurations specified in a yaml config file.
+"""
+import sys
+import os
+import yaml
+import tempfile
+
+CC = ""
+TEMPLATE = ""
+
+
+def usage():
+    print("Usage: CC=COMPILER {} CONFIG_PATH \
+OUTPUT_PATH_PREFIX".format(sys.argv[0]))
+    sys.exit(0)
+
+
+def str_to_c_byte_array(s):
+    """
+    Convert strings to byte-arrays so we don't worry about formatting
+    strings to play nicely with cc -DQEMU_FUZZARGS etc
+    """
+    return ','.join('0x{:02x}'.format(ord(x)) for x in s)
+
+
+def compile_wrapper(cfg, path):
+    os.system('$CC -DQEMU_FUZZ_ARGS="{}" -DQEMU_FUZZ_OBJECTS="{}" \
+                {} -o {}'.format(
+                    str_to_c_byte_array(cfg["args"].replace("\n", " ")),
+                    str_to_c_byte_array(cfg["objects"].replace("\n", " ")),
+                    TEMPLATE, path))
+
+
+def main():
+    global CC
+    global TEMPLATE
+
+    if len(sys.argv) != 3:
+        usage()
+
+    cfg_path = sys.argv[1]
+    out_path = sys.argv[2]
+
+    CC = os.getenv("CC")
+    TEMPLATE = os.path.join(os.path.dirname(__file__), "target.c")
+
+    with open(cfg_path, "r") as f:
+        configs = yaml.load(f)["configs"]
+    for cfg in configs:
+        assert "name" in cfg
+        assert "args" in cfg
+        assert "objects" in cfg
+        compile_wrapper(cfg, out_path + cfg["name"])
+
+
+if __name__ == '__main__':
+    main()
-- 
2.27.0

[PATCH 09/12] scripts/oss-fuzz: Add general-fuzzer configs for oss-fuzz

[Alexander Bulekov]

Each of these entries is built into a wrapper binary that sets the
needed environment variables and executes the general virtual-device
fuzzer. In the future, we will need additional fields, such as arch=arm,
timeout_per_testcase=0, reset=reboot, etc...

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
 scripts/oss-fuzz/general_fuzzer_configs.yml | 103 ++++++++++++++++++++
 1 file changed, 103 insertions(+)
 create mode 100644 scripts/oss-fuzz/general_fuzzer_configs.yml

diff --git a/scripts/oss-fuzz/general_fuzzer_configs.yml b/scripts/oss-fuzz/general_fuzzer_configs.yml
new file mode 100644
index 0000000000..748f4db075
--- /dev/null
+++ b/scripts/oss-fuzz/general_fuzzer_configs.yml
@@ -0,0 +1,103 @@
+configs:
+    - name: virtio-net-pci-slirp
+      args: >
+        -M q35 -nodefaults
+        -device virtio-net,netdev=net0 -netdev user,id=net0
+      objects: virtio*
+
+    - name: virtio-blk
+      args: >
+        -machine q35 -device virtio-blk,drive=disk0
+        -drive file=null-co://,id=disk0,if=none,format=raw
+      objects: virtio*
+
+    - name: virtio-scsi
+      args: >
+        -machine q35 -device virtio-scsi,num_queues=8
+        -device scsi-hd,drive=disk0
+        -drive file=null-co://,id=disk0,if=none,format=raw
+      objects: scsi* virtio*
+
+    - name: virtio-gpu
+      args: -machine q35 -nodefaults -device virtio-gpu
+      objects: virtio*
+
+    - name: virtio-vga
+      args: -machine q35 -nodefaults -device virtio-vga
+      objects: virtio*
+
+    - name: virtio-rng
+      args: -machine q35 -nodefaults -device virtio-rng
+      objects: virtio*
+
+    - name: virtio-balloon
+      args: -machine q35 -nodefaults -device virtio-balloon
+      objects: virtio*
+
+    - name: virtio-serial
+      args: -machine q35 -nodefaults -device virtio-serial
+      objects: virtio*
+
+    - name: virtio-mouse
+      args: -machine q35 -nodefaults -device virtio-mouse
+      objects: virtio*
+
+    - name: e1000
+      args: >
+        -M q35 -nodefaults
+        -device e1000,netdev=net0 -netdev user,id=net0
+      objects: e1000
+
+    - name: e1000e
+      args: >
+        -M q35 -nodefaults
+        -device e1000e,netdev=net0 -netdev user,id=net0
+      objects: e1000e
+
+    - name: cirrus-vga
+      args: -machine q35 -nodefaults -device cirrus-vga
+      objects: cirrus*
+
+    - name: bochs-display
+      args: -machine q35 -nodefaults -device bochs-display
+      objects: bochs*
+
+    - name: intel-hda
+      args: >
+        -machine q35 -nodefaults -device intel-hda,id=hda0
+        -device hda-output,bus=hda0.0 -device hda-micro,bus=hda0.0
+        -device hda-duplex,bus=hda0.0
+      objects: intel-hda
+
+    - name: ide-hd
+      args: >
+        -machine q35 -nodefaults
+        -drive file=null-co://,if=none,format=raw,id=disk0
+        -device ide-hd,drive=disk0
+      objects: ide
+
+    - name: floppy
+      args: >
+        -machine pc -nodefaults -device floppy,id=floppy0
+        -drive id=disk0,file=null-co://,file.read-zeroes=on,if=none
+        -device floppy,drive=disk0,drive-type=288
+      objects: fd floppy*
+
+    - name: xhci
+      args: >
+        -machine q35 -nodefaults
+        -drive file=null-co://,if=none,format=raw,id=disk0
+        -device qemu-xhci,id=xhci -device usb-tablet,bus=xhci.0 -device usb-bot
+        -device usb-storage,drive=disk0 -chardev null,id=cd0 -chardev null,id=cd1
+        -device usb-braille,chardev=cd0 -device usb-ccid -device usb-ccid
+        -device usb-kbd -device usb-mouse -device usb-serial,chardev=cd1
+        -device usb-tablet -device usb-wacom-tablet -device usb-audio
+      objects: "*"
+
+    - name: pc-i440fx
+      args: -machine pc
+      objects: "*"
+
+    - name: pc-q35
+      args: -machine q35
+      objects: "*"
-- 
2.27.0

[PATCH 10/12] scripts/oss-fuzz: build the general-fuzzer configs

[Alexander Bulekov]

Build general-fuzzer wrappers for each configuration defined in
general_fuzzer_configs.yml and move the actual general-fuzzer to a
subdirectory, so oss-fuzz doesn't treat it as a standalone fuzzer.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
 scripts/oss-fuzz/build.sh | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/scripts/oss-fuzz/build.sh b/scripts/oss-fuzz/build.sh
index a07b3022e8..2071e77ac2 100755
--- a/scripts/oss-fuzz/build.sh
+++ b/scripts/oss-fuzz/build.sh
@@ -38,7 +38,7 @@ OSS_FUZZ_BUILD_DIR="./build-oss-fuzz/"
 # remove it, resulting in an unresolved reference to qemu_build_not_reached
 # Undefine the __OPTIMIZE__ macro which compiler.h relies on to choose whether
 # to " #define qemu_build_not_reached()  g_assert_not_reached() "
-EXTRA_CFLAGS="$CFLAGS -U __OPTIMIZE__"
+EXTRA_CFLAGS="$CFLAGS -U __OPTIMIZE__ -DCONFIG_FUZZ=y"
 
 if ! { [ -e "./COPYING" ] &&
    [ -e "./MAINTAINERS" ] &&
@@ -101,5 +101,11 @@ do
     cp ./i386-softmmu/qemu-fuzz-i386 "$DEST_DIR/qemu-fuzz-i386-target-$target"
 done
 
+mkdir -p "$DEST_DIR/deps"
+mv "$DEST_DIR/qemu-fuzz-i386-target-general-fuzz" "$DEST_DIR/deps/"
+
+./scripts/oss-fuzz/build_general_fuzzers.py \
+    "./scripts/oss-fuzz/general_fuzzer_configs.yml" "$DEST_DIR/general-fuzz-"
+
 echo "Done. The fuzzers are located in $DEST_DIR"
 exit 0
-- 
2.27.0

[PATCH 11/12] scripts/oss-fuzz: Add script to reorder a general-fuzzer trace

[Alexander Bulekov]

The general-fuzzer uses hooks to fulfill DMA requests just-in-time.
This means that if we try to use QTEST_LOG=1 to build a reproducer, the
DMA writes will be logged _after_ the in/out/read/write that triggered
the DMA read. To work work around this, the general-fuzzer annotates
these just-in time DMA fulfilments with a tag that we can use to
discern them. This script simply iterates over a raw qtest
trace (including log messages, errors, timestamps etc), filters it and
re-orders it so that DMA fulfillments are placed directly _before_ the
qtest command that will cause the DMA access.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
 .../oss-fuzz/reorder_fuzzer_qtest_trace.py    | 94 +++++++++++++++++++
 1 file changed, 94 insertions(+)
 create mode 100755 scripts/oss-fuzz/reorder_fuzzer_qtest_trace.py

diff --git a/scripts/oss-fuzz/reorder_fuzzer_qtest_trace.py b/scripts/oss-fuzz/reorder_fuzzer_qtest_trace.py
new file mode 100755
index 0000000000..9fb7edb6ee
--- /dev/null
+++ b/scripts/oss-fuzz/reorder_fuzzer_qtest_trace.py
@@ -0,0 +1,94 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+"""
+Use this to convert qtest log info from a generic fuzzer input into a qtest
+trace that you can feed into a standard qemu-system process. Example usage:
+
+QEMU_FUZZ_ARGS="-machine q35,accel=qtest" QEMU_FUZZ_OBJECTS="*" \
+        ./i386-softmmu/qemu-fuzz-i386 --fuzz-target=general-pci-fuzz
+# .. Finds some crash
+QTEST_LOG=1 FUZZ_SERIALIZE_QTEST=1 \
+QEMU_FUZZ_ARGS="-machine q35,accel=qtest" QEMU_FUZZ_OBJECTS="*" \
+        ./i386-softmmu/qemu-fuzz-i386 --fuzz-target=general-pci-fuzz
+        /path/to/crash 2> qtest_log_output
+scripts/oss-fuzz/reorder_fuzzer_qtest_trace.py qtest_log_output > qtest_trace
+./i386-softmmu/qemu-fuzz-i386 -machine q35,accel=qtest \
+        -qtest stdin < qtest_trace
+
+### Details ###
+
+Some fuzzer make use of hooks that allow us to populate some memory range, just
+before a DMA read from that range. This means that the fuzzer can produce
+activity that looks like:
+    [start] read from mmio addr
+    [end]   read from mmio addr
+    [start] write to pio addr
+        [start] fill a DMA buffer just in time
+        [end]   fill a DMA buffer just in time
+        [start] fill a DMA buffer just in time
+        [end]   fill a DMA buffer just in time
+    [end]   write to pio addr
+    [start] read from mmio addr
+    [end]   read from mmio addr
+
+We annotate these "nested" DMA writes, so with QTEST_LOG=1 the QTest trace
+might look something like:
+[R +0.028431] readw 0x10000
+[R +0.028434] outl 0xc000 0xbeef  # Triggers a DMA read from 0xbeef and 0xbf00
+[DMA][R +0.034639] write 0xbeef 0x2 0xAAAA
+[DMA][R +0.034639] write 0xbf00 0x2 0xBBBB
+[R +0.028431] readw 0xfc000
+
+This script would reorder the above trace so it becomes:
+readw 0x10000
+write 0xbeef 0x2 0xAAAA
+write 0xbf00 0x2 0xBBBB
+outl 0xc000 0xbeef
+readw 0xfc000
+
+I.e. by the time, 0xc000 tries to read from DMA, those DMA buffers have already
+been set up, removing the need for the DMA hooks. We can simply provide this
+reordered trace via -qtest stdio to reproduce the input
+
+Note: this won't work for traces where the device tries to read from the same
+DMA region twice in between MMIO/PIO commands. E.g:
+    [R +0.028434] outl 0xc000 0xbeef
+    [DMA][R +0.034639] write 0xbeef 0x2 0xAAAA
+    [DMA][R +0.034639] write 0xbeef 0x2 0xBBBB
+"""
+
+import sys
+
+__author__     = "Alexander Bulekov <alxndr@bu.edu>"
+__copyright__  = "Copyright (C) 2020, Red Hat, Inc."
+__license__    = "GPL version 2 or (at your option) any later version"
+
+__maintainer__ = "Alexander Bulekov"
+__email__      = "alxndr@bu.edu"
+
+
+def usage():
+    sys.exit("Usage: {} /path/to/qtest_log_output".format((sys.argv[0])))
+
+
+def main(filename):
+    with open(filename, "r") as f:
+        trace = f.readlines()
+
+    # Leave only lines that look like logged qtest commands
+    trace[:] = [x.strip() for x in trace if "[R +" in x
+                or "[S +" in x and "CLOSED" not in x]
+
+    for i in range(len(trace)):
+        if i+1 < len(trace):
+            if "[DMA]" in trace[i+1]:
+                trace[i], trace[i+1] = trace[i+1], trace[i]
+    for line in trace:
+        print(line.split("]")[-1].strip())
+
+
+if __name__ == '__main__':
+    if len(sys.argv) == 1:
+        usage()
+    main(sys.argv[1])
-- 
2.27.0

[PATCH 12/12] scripts/oss-fuzz: Add crash trace minimization script

[Alexander Bulekov]

Once we find a crash, we can convert it into a QTest trace. Usually this
trace will contain many operations that are unneeded to reproduce the
crash. This script tries to minimize the crashing trace, by removing
operations and trimming QTest bufwrite(write addr len data...) commands.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
---
I know its hard to make sense of this patch and the previous one without
a real example, but I didn't want to delay sending this set. I'll try to
find and old crash (maybe for one of the e1000e bugs) and show exactly
how I go from binary libFuzzer blob to qtest reproducer.

 scripts/oss-fuzz/minimize_qtest_trace.py | 117 +++++++++++++++++++++++
 1 file changed, 117 insertions(+)
 create mode 100755 scripts/oss-fuzz/minimize_qtest_trace.py

diff --git a/scripts/oss-fuzz/minimize_qtest_trace.py b/scripts/oss-fuzz/minimize_qtest_trace.py
new file mode 100755
index 0000000000..c318032049
--- /dev/null
+++ b/scripts/oss-fuzz/minimize_qtest_trace.py
@@ -0,0 +1,117 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+"""
+This takes a crashing qtest trace and tries to remove superflous operations
+"""
+
+import sys
+import os
+import subprocess
+import time
+
+QEMU_ARGS = None
+QEMU_PATH = None
+TIMEOUT = 5
+CRASH_TOKEN = None
+
+
+def usage():
+    sys.exit("""\
+Usage: QEMU_PATH="/path/to/qemu" QEMU_ARGS="args" {} input_trace output_trace
+By default, will try to use the second-to-last line in the output to identify
+whether the crash occred. Optionally, manually set a string that idenitifes the
+crash by setting CRASH_TOKEN=
+""".format((sys.argv[0])))
+
+
+def check_if_trace_crashes(trace, path):
+    global CRASH_TOKEN
+    with open(path, "w") as tracefile:
+        tracefile.write("".join(trace))
+    rc = subprocess.Popen("timeout -s 9 {}s {} {} 2>&1 < {}".format(TIMEOUT,
+                          QEMU_PATH, QEMU_ARGS, path),
+                          shell=True, stdin=subprocess.PIPE,
+                          stdout=subprocess.PIPE)
+    stdo, None = rc.communicate()
+    output = stdo.decode('unicode_escape')
+    if rc.returncode == 137:    # Timed Out
+        return False
+    if len(output.splitlines()) < 2:
+        return False
+
+    if CRASH_TOKEN is None:
+        CRASH_TOKEN = output.splitlines()[-2]
+
+    return CRASH_TOKEN in output
+
+
+def minimize_trace(inpath, outpath):
+    global TIMEOUT
+    with open(inpath) as f:
+        trace = f.readlines()
+    start = time.time()
+    if not check_if_trace_crashes(trace, outpath):
+        sys.exit("The input qtest trace didn't cause a crash...")
+    end = time.time()
+    print("Crashed in {} seconds".format(end-start))
+    TIMEOUT = (end-start)*5
+    print("Setting the timeout for {} seconds".format(TIMEOUT))
+    print("Identifying Crashes by this string: {}".format(CRASH_TOKEN))
+
+    i = 0
+    newtrace = trace[:]
+    while i < len(newtrace):
+        prior = newtrace[i]
+        # Try to remove the line completely
+        newtrace[i] = ""
+        if check_if_trace_crashes(newtrace, outpath):
+            i += 1
+            continue
+        newtrace[i] = prior
+        # Try to split up writes into multiple commands, each of which can be
+        # removed.
+        if newtrace[i].startswith("write "):
+            addr = int(newtrace[i].split()[1], 16)
+            length = int(newtrace[i].split()[2], 16)
+            data = newtrace[i].split()[3][2:]
+            if length > 1:
+                leftlength = int(length/2)
+                rightlength = length - leftlength
+                newtrace.insert(i+1, "")
+                while leftlength > 0:
+                    newtrace[i] = "write {} {} 0x{}\n".format(
+                            hex(addr),
+                            hex(leftlength),
+                            data[:leftlength*2])
+                    newtrace[i+1] = "write {} {} 0x{}\n".format(
+                            hex(addr+leftlength),
+                            hex(rightlength),
+                            data[leftlength*2:])
+                    if check_if_trace_crashes(newtrace, outpath):
+                        break
+                    else:
+                        leftlength -= 1
+                        rightlength += 1
+                if check_if_trace_crashes(newtrace, outpath):
+                    i -= 1
+                else:
+                    newtrace[i] = prior
+                    del newtrace[i+1]
+        i += 1
+    check_if_trace_crashes(newtrace, outpath)
+
+
+if __name__ == '__main__':
+    if len(sys.argv) < 3:
+        usage()
+
+    QEMU_PATH = os.getenv("QEMU_PATH")
+    QEMU_ARGS = os.getenv("QEMU_ARGS")
+    if QEMU_PATH is None or QEMU_ARGS is None:
+        usage()
+    if "accel" not in QEMU_ARGS:
+        QEMU_ARGS += " -accel qtest"
+    CRASH_TOKEN = os.getenv(CRASH_TOKEN)
+    QEMU_ARGS += " -qtest stdio -monitor none -serial none "
+    minimize_trace(sys.argv[1], sys.argv[2])
-- 
2.27.0

Re: [PATCH 01/12] fuzz: Change the way we write qtest log to stderr

[Darren Kenny]

On Wednesday, 2020-07-22 at 23:39:22 -04, Alexander Bulekov wrote:
> Telling QTest to log to /dev/fd/2, essentially results in dup(2). This
> is fine, if other code isn't logging to stderr. Otherwise, the order of
> the logs is mixed due to buffering issues, since two file-descriptors
> are used to write to the same file. We can avoid this, since just
> specifying "-qtest" sets the log fd to stderr. If we want to disable
> qtest logs, we can just add -qtest-log none.
>
> Signed-off-by: Alexander Bulekov <alxndr@bu.edu>

Reviewed-by: Darren Kenny <darren.kenny@oracle.com>

> ---
>  tests/qtest/fuzz/fuzz.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/tests/qtest/fuzz/fuzz.c b/tests/qtest/fuzz/fuzz.c
> index 031594a686..8234b68754 100644
> --- a/tests/qtest/fuzz/fuzz.c
> +++ b/tests/qtest/fuzz/fuzz.c
> @@ -202,9 +202,8 @@ int LLVMFuzzerInitialize(int *argc, char ***argv, char ***envp)
>  
>      /* Run QEMU's softmmu main with the fuzz-target dependent arguments */
>      GString *cmd_line = fuzz_target->get_init_cmdline(fuzz_target);
> -    g_string_append_printf(cmd_line,
> -                           " -qtest /dev/null -qtest-log %s",
> -                           getenv("QTEST_LOG") ? "/dev/fd/2" : "/dev/null");
> +    g_string_append_printf(cmd_line, " %s -qtest /dev/null ",
> +                           getenv("QTEST_LOG") ? "" : "-qtest-log none");
>  
>      /* Split the runcmd into an argv and argc */
>      wordexp_t result;
> -- 
> 2.27.0

Re: [PATCH 02/12] fuzz: Add general virtual-device fuzzer

[Alexander Bulekov]

On 200722 2339, Alexander Bulekov wrote:
> 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   | 467 ++++++++++++++++++++++++++++++
>  2 files changed, 468 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..fd92cc5bdf
> --- /dev/null
> +++ b/tests/qtest/fuzz/general_fuzz.c
> @@ -0,0 +1,467 @@
> +/*
> + * 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"
> +
> +/*
> + * CMD_SEP is a random 32-bit value used to separate "commands" in the fuzz
> + * input
> + */
> +#define CMD_SEP "\x84\x05\x5C\x5E"
> +#define DEFAULT_TIMEOUT_US 100000
> +
> +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;
> +
> +    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) {

Theres a problem here. This finds an aboslute address for an index
+ offset in our fuzzable_memory_regions array, but doesn't check that
the MemoryRegion has the highest priority for that address.
I think the way to solve this is to do the opposite
address_space_translate and ensure that the MemoryRegion* we get back is
the same MemoryRegion* that is in our fuzzable_memory_regions array.

Only noticed this as I was trying to fuzz an audio device and saw that
by fuzzing the device's PCI space the fuzzer would set the BAR over an
existing higher-priority device and the fuzzer was exercising code for
that device.
-Alex

> +                ind--;
> +                candidate_regions++;
> +                result->addr = abs_addr + (offset % mr->size);
> +                result->len = mr->size - (offset % mr->size);
> +            }
> +        }
> +        ++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, CMD_SEP, 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 CMD_SEP 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_out,
> +        op_read,
> +        op_write,
> +        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;
> +            sigemptyset(&sact.sa_mask);
> +            sact.sa_flags = 0;
> +            sact.sa_handler = handle_timeout;
> +            sigaction(SIGALRM, &sact, NULL);
> +            ualarm(timeout, 0);
> +        }
> +
> +        while (cmd && Size) {
> +            /* Get the length until the next command or end of input */
> +            nextcmd = memmem(cmd, Size, CMD_SEP, strlen(CMD_SEP));
> +            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(CMD_SEP) - 1 : nextcmd;
> +            Size = Size - (cmd_len + sizeof(CMD_SEP) - 1);
> +        }
> +        _Exit(0);
> +    } else {
> +        flush_events(s);
> +        wait(NULL);
> +    }
> +}
> +
> +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))) {
> +        printf("Matched Object by Type: %s\n", 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();
> +    wordexp_t result;
> +    wordexp(getenv("QEMU_FUZZ_OBJECTS"), &result, 0);
> +    for (int i = 0; i < result.we_wordc; i++) {
> +        object_child_foreach_recursive(qdev_get_machine(),
> +                                    locate_fuzz_objects,
> +                                    result.we_wordv[i]);
> +    }
> +
> +    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);
> +    }
> +    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
> 

Re: [PATCH 00/12] Add a General Virtual Device Fuzzer

[Dima Stepanov]

Hi Alex,

Thanks for the nice general fuzzer implementation, looks pretty
exciting. Are there any future plans discussion which i can read
or maybe join? I have some ideas about it so it could be great to
syncronize.

Regards, Dima.

On Wed, Jul 22, 2020 at 11:39:21PM -0400, Alexander Bulekov wrote:
> This is a general virtual-device fuzzer, designed to fuzz devices over Port IO,
> MMIO, and DMA.
> To get started with this:
>  1. Build the fuzzers (see docs/devel/fuzzing.txt)
>     Note: Build with --enable-sanitizers, or create a "dictionary file":
>     echo kw1=\"\x84\x05\x5C\x5E\" > dict
>     and pass it as an argument to libFuzzer with -dict=./dict
>     This magic value is a command separator that lets the fuzzer perform
>     multiple IO actions with a single input.
> 
>  2. Pick the qemu arguments you wish to fuzz:
>     export QEMU_FUZZ_ARGS="-M q35 -device virtio-balloon"
> 
>  3. Tell the fuzzer which QOM objects or MemoryRegion names to fuzz. I find the
>  "info qom-tree", "info qtree" and "info mtree" commands useful for identifying
>  these. Supports globbing. Here I will try to simultaneously fuzz(for no good
>  reason) virtio-balloon and e1000e, which is included by default in the q35:
>     export QEMU_FUZZ_OBJECTS='virtio* e1000*'
>     You can also try to fuzz the whole machine:
>     export QEMU_FUZZ_OBJECTS='*'
> 
>  4. Run the fuzzer for 0 inputs. The fuzzer should output a list of
>  MemoryRegions/PCI Devices it will try to fuzz. Confirm that these match your
>  expectations.
>     ./i386-softmmu/qemu-fuzz-i386 --fuzz-target=general-fuzz -runs=0
> 
>  5. Run the fuzzer:
>     ./i386-softmmu/qemu-fuzz-i386 --fuzz-target=general-fuzz 
> 
> 
> Basically, at the core, this fuzzer is an interpreter that splits the input
> into a series of commands, such as mmio_write, pio_write, etc. We structure
> these commands to hit only MemoryRegions that are associated with the devices
> specified in QEMU_FUZZ_OBJECTS. Additionally, these patches add "hooks" to
> functions that are typically used by virtual-devices to read from RAM (DMA).
> These hooks attempt to populate these DMA regions with fuzzed data, just in
> time.
> 
> Patch 1 changes the way we tell QTest to log to stderr (becomes important when
> building reproducers with this fuzzer)
> 
> Patches 2-6 add the fuzzer and the necessary DMA callbacks
> 
> Patches 7-10 are my (very rough) attempt at integrating this into OSS-Fuzz
> 
> Patches 11-12 contain the "reordering" and minimization scripts used to
> produce a QTest reproducer for a crash.
> 
> Additional notes:
>  * With the latest changes, the
>  fuzzer is quite effective at only targeting the device we care about,
>  so it will probably be beneficial to allow reboot() as an option for
>  resetting state, rather than fork(), for devices where that works well.
> 
>  * We have only scratched the surface for device "backends". I.e. I am using
>  fake null-co:// drives for block devices and SLiRP for network devices (see
>  scripts/oss-fuzz/general_fuzzer_configs.yml). Using more complex backends will
>  likely break due to forking/threading/statefulness related reasons and will
>  require more work.
> 
> * Because I still can't figure out how to make QOS do what I want, this
>   only maps PCI BARs on i386. For other targets, the fuzzer can still
>   try to do it on its own :). Only did a very simple test on ppc and arm
> 
>  * This is failing on GitLab due to a leak:
>  https://gitlab.com/a1xndr/qemu/-/jobs/652179729
>  I am not sure how to work around it yet, since I don't think we can
>  free what the trace says we should free (argv from wordexp that we pass
>  to qemu_main).
> 
> 
> Some of the issues I have found or reproduced with this fuzzer:
> https://bugs.launchpad.net/bugs/1525123
> https://bugs.launchpad.net/bugs/1681439
> https://bugs.launchpad.net/bugs/1777315
> https://bugs.launchpad.net/bugs/1878034
> https://bugs.launchpad.net/bugs/1878043
> https://bugs.launchpad.net/bugs/1878054
> https://bugs.launchpad.net/bugs/1878057
> https://bugs.launchpad.net/bugs/1878067
> https://bugs.launchpad.net/bugs/1878134
> https://bugs.launchpad.net/bugs/1878136
> https://bugs.launchpad.net/bugs/1878253
> https://bugs.launchpad.net/bugs/1878255
> https://bugs.launchpad.net/bugs/1878259
> https://bugs.launchpad.net/bugs/1878263
> https://bugs.launchpad.net/bugs/1878323
> https://bugs.launchpad.net/bugs/1878641
> https://bugs.launchpad.net/bugs/1878642
> https://bugs.launchpad.net/bugs/1878645
> https://bugs.launchpad.net/bugs/1878651
> https://bugs.launchpad.net/bugs/1879223
> https://bugs.launchpad.net/bugs/1879227
> https://bugs.launchpad.net/bugs/1879531
> https://bugs.launchpad.net/bugs/1880355
> https://bugs.launchpad.net/bugs/1880539
> https://bugs.launchpad.net/bugs/1884693
> https://bugs.launchpad.net/bugs/1886362
> https://bugs.launchpad.net/bugs/1887303
> https://bugs.launchpad.net/bugs/1887309
> https://bugs.launchpad.net/bugs/697510
> 
> -Alex
> 
> Alexander Bulekov (12):
>   fuzz: Change the way we write qtest log to stderr
>   fuzz: Add general virtual-device fuzzer
>   fuzz: Add PCI features to the general fuzzer
>   fuzz: Add DMA support to the generic-fuzzer
>   fuzz: Declare DMA Read callback function
>   fuzz: Add fuzzer callbacks to DMA-read functions
>   scripts/oss-fuzz: Add wrapper program for generic fuzzer
>   scripts/oss-fuzz: Add general-fuzzer build script
>   scripts/oss-fuzz: Add general-fuzzer configs for oss-fuzz
>   scripts/oss-fuzz: build the general-fuzzer configs
>   scripts/oss-fuzz: Add script to reorder a general-fuzzer trace
>   scripts/oss-fuzz: Add crash trace minimization script
> 
>  exec.c                                        |   2 +
>  include/exec/memory.h                         |  16 +
>  include/exec/memory_ldst_cached.inc.h         |   3 +
>  memory_ldst.inc.c                             |   4 +
>  scripts/oss-fuzz/build.sh                     |   8 +-
>  scripts/oss-fuzz/build_general_fuzzers.py     |  62 ++
>  scripts/oss-fuzz/general_fuzzer_configs.yml   | 103 +++
>  scripts/oss-fuzz/minimize_qtest_trace.py      | 117 +++
>  .../oss-fuzz/reorder_fuzzer_qtest_trace.py    |  94 +++
>  scripts/oss-fuzz/target.c                     |  40 +
>  softmmu/memory.c                              |  14 +
>  tests/qtest/fuzz/Makefile.include             |   1 +
>  tests/qtest/fuzz/fuzz.c                       |   5 +-
>  tests/qtest/fuzz/general_fuzz.c               | 758 ++++++++++++++++++
>  14 files changed, 1223 insertions(+), 4 deletions(-)
>  create mode 100755 scripts/oss-fuzz/build_general_fuzzers.py
>  create mode 100644 scripts/oss-fuzz/general_fuzzer_configs.yml
>  create mode 100755 scripts/oss-fuzz/minimize_qtest_trace.py
>  create mode 100755 scripts/oss-fuzz/reorder_fuzzer_qtest_trace.py
>  create mode 100644 scripts/oss-fuzz/target.c
>  create mode 100644 tests/qtest/fuzz/general_fuzz.c
> 
> -- 
> 2.27.0
> 

Re: [PATCH 00/12] Add a General Virtual Device Fuzzer

[Alexander Bulekov]

On 200826 1410, Dima Stepanov wrote:
> Hi Alex,
> 
> Thanks for the nice general fuzzer implementation, looks pretty
> exciting. Are there any future plans discussion which i can read
> or maybe join? I have some ideas about it so it could be great to
> syncronize.
> 
> Regards, Dima.

Hi Dima,
Apologies about the late response - I needed to catch up on some
academic work but things seem to be going back to normal now. We have
fuzzing meetings at 10 AM on Thursdays. Does this work for you? 
Thanks!
-Alex

> On Wed, Jul 22, 2020 at 11:39:21PM -0400, Alexander Bulekov wrote:
> > This is a general virtual-device fuzzer, designed to fuzz devices over Port IO,
> > MMIO, and DMA.
> > To get started with this:
> >  1. Build the fuzzers (see docs/devel/fuzzing.txt)
> >     Note: Build with --enable-sanitizers, or create a "dictionary file":
> >     echo kw1=\"\x84\x05\x5C\x5E\" > dict
> >     and pass it as an argument to libFuzzer with -dict=./dict
> >     This magic value is a command separator that lets the fuzzer perform
> >     multiple IO actions with a single input.
> > 
> >  2. Pick the qemu arguments you wish to fuzz:
> >     export QEMU_FUZZ_ARGS="-M q35 -device virtio-balloon"
> > 
> >  3. Tell the fuzzer which QOM objects or MemoryRegion names to fuzz. I find the
> >  "info qom-tree", "info qtree" and "info mtree" commands useful for identifying
> >  these. Supports globbing. Here I will try to simultaneously fuzz(for no good
> >  reason) virtio-balloon and e1000e, which is included by default in the q35:
> >     export QEMU_FUZZ_OBJECTS='virtio* e1000*'
> >     You can also try to fuzz the whole machine:
> >     export QEMU_FUZZ_OBJECTS='*'
> > 
> >  4. Run the fuzzer for 0 inputs. The fuzzer should output a list of
> >  MemoryRegions/PCI Devices it will try to fuzz. Confirm that these match your
> >  expectations.
> >     ./i386-softmmu/qemu-fuzz-i386 --fuzz-target=general-fuzz -runs=0
> > 
> >  5. Run the fuzzer:
> >     ./i386-softmmu/qemu-fuzz-i386 --fuzz-target=general-fuzz 
> > 
> > 
> > Basically, at the core, this fuzzer is an interpreter that splits the input
> > into a series of commands, such as mmio_write, pio_write, etc. We structure
> > these commands to hit only MemoryRegions that are associated with the devices
> > specified in QEMU_FUZZ_OBJECTS. Additionally, these patches add "hooks" to
> > functions that are typically used by virtual-devices to read from RAM (DMA).
> > These hooks attempt to populate these DMA regions with fuzzed data, just in
> > time.
> > 
> > Patch 1 changes the way we tell QTest to log to stderr (becomes important when
> > building reproducers with this fuzzer)
> > 
> > Patches 2-6 add the fuzzer and the necessary DMA callbacks
> > 
> > Patches 7-10 are my (very rough) attempt at integrating this into OSS-Fuzz
> > 
> > Patches 11-12 contain the "reordering" and minimization scripts used to
> > produce a QTest reproducer for a crash.
> > 
> > Additional notes:
> >  * With the latest changes, the
> >  fuzzer is quite effective at only targeting the device we care about,
> >  so it will probably be beneficial to allow reboot() as an option for
> >  resetting state, rather than fork(), for devices where that works well.
> > 
> >  * We have only scratched the surface for device "backends". I.e. I am using
> >  fake null-co:// drives for block devices and SLiRP for network devices (see
> >  scripts/oss-fuzz/general_fuzzer_configs.yml). Using more complex backends will
> >  likely break due to forking/threading/statefulness related reasons and will
> >  require more work.
> > 
> > * Because I still can't figure out how to make QOS do what I want, this
> >   only maps PCI BARs on i386. For other targets, the fuzzer can still
> >   try to do it on its own :). Only did a very simple test on ppc and arm
> > 
> >  * This is failing on GitLab due to a leak:
> >  https://gitlab.com/a1xndr/qemu/-/jobs/652179729
> >  I am not sure how to work around it yet, since I don't think we can
> >  free what the trace says we should free (argv from wordexp that we pass
> >  to qemu_main).
> > 
> > 
> > Some of the issues I have found or reproduced with this fuzzer:
> > https://bugs.launchpad.net/bugs/1525123
> > https://bugs.launchpad.net/bugs/1681439
> > https://bugs.launchpad.net/bugs/1777315
> > https://bugs.launchpad.net/bugs/1878034
> > https://bugs.launchpad.net/bugs/1878043
> > https://bugs.launchpad.net/bugs/1878054
> > https://bugs.launchpad.net/bugs/1878057
> > https://bugs.launchpad.net/bugs/1878067
> > https://bugs.launchpad.net/bugs/1878134
> > https://bugs.launchpad.net/bugs/1878136
> > https://bugs.launchpad.net/bugs/1878253
> > https://bugs.launchpad.net/bugs/1878255
> > https://bugs.launchpad.net/bugs/1878259
> > https://bugs.launchpad.net/bugs/1878263
> > https://bugs.launchpad.net/bugs/1878323
> > https://bugs.launchpad.net/bugs/1878641
> > https://bugs.launchpad.net/bugs/1878642
> > https://bugs.launchpad.net/bugs/1878645
> > https://bugs.launchpad.net/bugs/1878651
> > https://bugs.launchpad.net/bugs/1879223
> > https://bugs.launchpad.net/bugs/1879227
> > https://bugs.launchpad.net/bugs/1879531
> > https://bugs.launchpad.net/bugs/1880355
> > https://bugs.launchpad.net/bugs/1880539
> > https://bugs.launchpad.net/bugs/1884693
> > https://bugs.launchpad.net/bugs/1886362
> > https://bugs.launchpad.net/bugs/1887303
> > https://bugs.launchpad.net/bugs/1887309
> > https://bugs.launchpad.net/bugs/697510
> > 
> > -Alex
> > 
> > Alexander Bulekov (12):
> >   fuzz: Change the way we write qtest log to stderr
> >   fuzz: Add general virtual-device fuzzer
> >   fuzz: Add PCI features to the general fuzzer
> >   fuzz: Add DMA support to the generic-fuzzer
> >   fuzz: Declare DMA Read callback function
> >   fuzz: Add fuzzer callbacks to DMA-read functions
> >   scripts/oss-fuzz: Add wrapper program for generic fuzzer
> >   scripts/oss-fuzz: Add general-fuzzer build script
> >   scripts/oss-fuzz: Add general-fuzzer configs for oss-fuzz
> >   scripts/oss-fuzz: build the general-fuzzer configs
> >   scripts/oss-fuzz: Add script to reorder a general-fuzzer trace
> >   scripts/oss-fuzz: Add crash trace minimization script
> > 
> >  exec.c                                        |   2 +
> >  include/exec/memory.h                         |  16 +
> >  include/exec/memory_ldst_cached.inc.h         |   3 +
> >  memory_ldst.inc.c                             |   4 +
> >  scripts/oss-fuzz/build.sh                     |   8 +-
> >  scripts/oss-fuzz/build_general_fuzzers.py     |  62 ++
> >  scripts/oss-fuzz/general_fuzzer_configs.yml   | 103 +++
> >  scripts/oss-fuzz/minimize_qtest_trace.py      | 117 +++
> >  .../oss-fuzz/reorder_fuzzer_qtest_trace.py    |  94 +++
> >  scripts/oss-fuzz/target.c                     |  40 +
> >  softmmu/memory.c                              |  14 +
> >  tests/qtest/fuzz/Makefile.include             |   1 +
> >  tests/qtest/fuzz/fuzz.c                       |   5 +-
> >  tests/qtest/fuzz/general_fuzz.c               | 758 ++++++++++++++++++
> >  14 files changed, 1223 insertions(+), 4 deletions(-)
> >  create mode 100755 scripts/oss-fuzz/build_general_fuzzers.py
> >  create mode 100644 scripts/oss-fuzz/general_fuzzer_configs.yml
> >  create mode 100755 scripts/oss-fuzz/minimize_qtest_trace.py
> >  create mode 100755 scripts/oss-fuzz/reorder_fuzzer_qtest_trace.py
> >  create mode 100644 scripts/oss-fuzz/target.c
> >  create mode 100644 tests/qtest/fuzz/general_fuzz.c
> > 
> > -- 
> > 2.27.0
> > 
>