Re: [PATCH v3 02/16] fuzz: Add general virtual-device fuzzer

[Philippe Mathieu-Daudé]

Hi Alexander,

On 9/21/20 4:24 AM, 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/general_fuzz.c | 498 ++++++++++++++++++++++++++++++++
>  tests/qtest/fuzz/meson.build    |   1 +
>  2 files changed, 499 insertions(+)
>  create mode 100644 tests/qtest/fuzz/general_fuzz.c
> 
> diff --git a/tests/qtest/fuzz/general_fuzz.c b/tests/qtest/fuzz/general_fuzz.c
> new file mode 100644
> index 0000000000..bf75b215ca
> --- /dev/null
> +++ b/tests/qtest/fuzz/general_fuzz.c
> @@ -0,0 +1,498 @@
> +/*
> + * 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 "hw/core/cpu.h"
> +#include "tests/qtest/libqos/libqtest.h"
> +#include "fuzz.h"
> +#include "fork_fuzz.h"
> +#include "exec/address-spaces.h"
> +#include "string.h"
> +#include "exec/memory.h"
> +#include "exec/ramblock.h"
> +#include "exec/address-spaces.h"
> +#include "hw/qdev-core.h"
> +
> +/*
> + * SEPARATOR is used to separate "operations" in the fuzz input
> + */
> +#define SEPARATOR "FUZZ"

Why use a separator when all pkt sizes are known?

Can you fuzz writing "FUZZ" in memory? Like:
OP_WRITE(0x100000, "UsingLibFUZZerString")?

> +
> +enum cmds {
> +    OP_IN,
> +    OP_OUT,
> +    OP_READ,
> +    OP_WRITE,
> +    OP_CLOCK_STEP,
> +};
> +
> +#define DEFAULT_TIMEOUT_US 100000
> +#define USEC_IN_SEC 100000000

Are you sure this definition is correct?

> +
> +typedef struct {
> +    ram_addr_t addr;
> +    ram_addr_t size; /* The number of bytes until the end of the I/O region 
> */
> +} address_range;
> +
> +static useconds_t timeout = 100000;
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