Re: [PATCH v3 09/16] fuzz: add a crossover function to generic-fuzzer

[Alexander Bulekov]

Thanks, I added some clarifications, but I added them to 02/16 (where I
first define and use SEPARATOR).

On 201001 1631, Darren Kenny wrote:
> As mentioned in an earlier patch, maybe the definition of SEPARATOR
> should be here as well as some of the comments you provided in the
> replies to it.
> 
> Otherwise, this looks good,
> 
> Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
> 
> Thanks,
> 
> Darren.
> 
> On Sunday, 2020-09-20 at 22:24:59 -04, Alexander Bulekov wrote:
> > Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
> > ---
> >  tests/qtest/fuzz/general_fuzz.c | 90 ++++++++++++++++++++++++++++++++-
> >  1 file changed, 89 insertions(+), 1 deletion(-)
> >
> > diff --git a/tests/qtest/fuzz/general_fuzz.c 
> > b/tests/qtest/fuzz/general_fuzz.c
> > index 656ec7fd55..3833b505c8 100644
> > --- a/tests/qtest/fuzz/general_fuzz.c
> > +++ b/tests/qtest/fuzz/general_fuzz.c
> > @@ -741,6 +741,92 @@ static void general_pre_fuzz(QTestState *s)
> >  
> >      counter_shm_init();
> >  }
> > +
> > +/*
> > + * When libfuzzer gives us two inputs to combine, return a new input with 
> > the
> > + * following structure:
> > + *
> > + * Input 1 (data1)
> > + * SEPARATOR
> > + * Clear out the DMA Patterns
> > + * SEPARATOR
> > + * Disable the pci_read/write instructions
> > + * SEPARATOR
> > + * Input 2 (data2)
> > + *
> > + * The idea is to collate the core behaviors of the two inputs.
> > + * For example:
> > + * Input 1: maps a device's BARs, sets up three DMA patterns, and triggers
> > + *          device functionality A
> > + * Input 2: maps a device's BARs, sets up one DMA pattern, and triggers 
> > device
> > + *          functionality B
> > + *
> > + * This function attempts to produce an input that:
> > + * Ouptut: maps a device's BARs, set up three DMA patterns, triggers
> > + *          functionality A device, replaces the DMA patterns with a single
> > + *          patten, and triggers device functionality B.
> > + */
> > +static size_t general_fuzz_crossover(const uint8_t *data1, size_t size1, 
> > const
> > +                                     uint8_t *data2, size_t size2, uint8_t 
> > *out,
> > +                                     size_t max_out_size, unsigned int 
> > seed)
> > +{
> > +    size_t copy_len = 0, size = 0;
> > +
> > +    /* Check that we have enough space for data1 and at least part of 
> > data2 */
> > +    if (max_out_size <= size + strlen(SEPARATOR) * 3 + 2) {
> > +        return 0;
> > +    }
> > +
> > +    /* Copy_Len in the first input */
> > +    copy_len = size1;
> > +    memcpy(out + size, data1, copy_len);
> > +    size += copy_len;
> > +    max_out_size -= copy_len;
> > +
> > +    /* Append a separator */
> > +    copy_len = strlen(SEPARATOR);
> > +    memcpy(out + size, SEPARATOR, copy_len);
> > +    size += copy_len;
> > +    max_out_size -= copy_len;
> > +
> > +    /* Clear out the DMA Patterns */
> > +    copy_len = 1;
> > +    if (copy_len) {
> > +        out[size] = OP_CLEAR_DMA_PATTERNS;
> > +    }
> > +    size += copy_len;
> > +    max_out_size -= copy_len;
> > +
> > +    /* Append a separator */
> > +    copy_len = strlen(SEPARATOR);
> > +    memcpy(out + size, SEPARATOR, copy_len);
> > +    size += copy_len;
> > +    max_out_size -= copy_len;
> > +
> > +    /* Disable PCI ops. Assume data1 took care of setting up PCI */
> > +    copy_len = 1;
> > +    if (copy_len) {
> > +        out[size] = OP_DISABLE_PCI;
> > +    }
> > +    size += copy_len;
> > +    max_out_size -= copy_len;
> > +
> > +    /* Append a separator */
> > +    copy_len = strlen(SEPARATOR);
> > +    memcpy(out + size, SEPARATOR, copy_len);
> > +    size += copy_len;
> > +    max_out_size -= copy_len;
> > +
> > +    /* Copy_Len over the second input */
> > +    copy_len = MIN(size2, max_out_size);
> > +    memcpy(out + size, data2, copy_len);
> > +    size += copy_len;
> > +    max_out_size -= copy_len;
> > +
> > +    return  size;
> > +}
> > +
> > +
> >  static GString *general_fuzz_cmdline(FuzzTarget *t)
> >  {
> >      GString *cmd_line = g_string_new(TARGET_NAME);
> > @@ -760,7 +846,9 @@ static void register_general_fuzz_targets(void)
> >              .description = "Fuzz based on any qemu command-line args. ",
> >              .get_init_cmdline = general_fuzz_cmdline,
> >              .pre_fuzz = general_pre_fuzz,
> > -            .fuzz = general_fuzz});
> > +            .fuzz = general_fuzz,
> > +            .crossover = general_fuzz_crossover
> > +    });
> >  }
> >  
> >  fuzz_target_init(register_general_fuzz_targets);
> > -- 
> > 2.28.0