On Wednesday, 2021-06-23 at 23:45:00 -04, Alexander Bulekov wrote: > Using a custom timeout is useful to continue fuzzing complex devices, > even after we run into some slow code-path. However, simply adding a > fixed timeout to each input effectively caps the maximum input > length/number of operations at some artificial value. There are two > major problems with this: > 1. Some code might only be reachable through long IO sequences. > 2. Longer inputs can actually be _better_ for performance. While the > raw number of fuzzer executions decreases with larger inputs, the > number of MMIO/PIO/DMA operation/second actually increases, since > were are speding proportionately less time fork()ing. > > With this change, we keep the custom-timeout, but we renew it, prior to > each MMIO/PIO/DMA operation. Thus, we time-out only when a particaly
TYPO: s/particaly/specific/ or s/particaly/particular/ ? > operation takes a long time. > > Signed-off-by: Alexander Bulekov <alx...@bu.edu> Otherwise, Reviewed-by: Darren Kenny <darren.ke...@oracle.com> Thanks, Darren. > --- > tests/qtest/fuzz/generic_fuzz.c | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) > > diff --git a/tests/qtest/fuzz/generic_fuzz.c b/tests/qtest/fuzz/generic_fuzz.c > index cea7d4058e..71d36e8f6f 100644 > --- a/tests/qtest/fuzz/generic_fuzz.c > +++ b/tests/qtest/fuzz/generic_fuzz.c > @@ -661,15 +661,16 @@ static void generic_fuzz(QTestState *s, const unsigned > char *Data, size_t Size) > uint8_t op; > > if (fork() == 0) { > + struct sigaction sact; > + struct itimerval timer; > /* > * 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 > + * fuzzer, overall. Set a timeout for each command to avoid hurting > + * performance, too much > */ > if (timeout) { > - struct sigaction sact; > - struct itimerval timer; > > sigemptyset(&sact.sa_mask); > sact.sa_flags = SA_NODEFER; > @@ -679,13 +680,17 @@ static void generic_fuzz(QTestState *s, const unsigned > char *Data, size_t Size) > memset(&timer, 0, sizeof(timer)); > timer.it_value.tv_sec = timeout / USEC_IN_SEC; > timer.it_value.tv_usec = timeout % USEC_IN_SEC; > - setitimer(ITIMER_VIRTUAL, &timer, NULL); > } > > op_clear_dma_patterns(s, NULL, 0); > pci_disabled = false; > > while (cmd && Size) { > + /* Reset the timeout, each time we run a new command */ > + if (timeout) { > + setitimer(ITIMER_VIRTUAL, &timer, NULL); > + } > + > /* Get the length until the next command or end of input */ > nextcmd = memmem(cmd, Size, SEPARATOR, strlen(SEPARATOR)); > cmd_len = nextcmd ? nextcmd - cmd : Size; > -- > 2.28.0