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Thu, 24 Jun 2021 09:23:14 +0000 From: Darren Kenny To: Alexander Bulekov , qemu-devel@nongnu.org Subject: Re: [PATCH v3 1/4] fuzz: adjust timeout to allow for longer inputs In-Reply-To: <20210624034503.86256-2-alxndr@bu.edu> References: <20210624034503.86256-1-alxndr@bu.edu> <20210624034503.86256-2-alxndr@bu.edu> Date: Thu, 24 Jun 2021 10:23:10 +0100 Message-ID: Content-Type: text/plain X-Originating-IP: [79.97.215.145] X-ClientProxiedBy: DU2PR04CA0001.eurprd04.prod.outlook.com (2603:10a6:10:3b::6) To BLAPR10MB5138.namprd10.prod.outlook.com (2603:10b6:208:322::8) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from oracle.com (79.97.215.145) by DU2PR04CA0001.eurprd04.prod.outlook.com (2603:10a6:10:3b::6) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4264.18 via Frontend Transport; Thu, 24 Jun 2021 09:23:13 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 57f3aa0a-49ac-456f-7e13-08d936f1b151 X-MS-TrafficTypeDiagnostic: MN2PR10MB4238: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:1122; 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envelope-from=darren.kenny@oracle.com; helo=mx0b-00069f02.pphosted.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Laurent Vivier , Thomas Huth , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Alexander Bulekov , Bandan Das , Stefan Hajnoczi , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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 Otherwise, Reviewed-by: Darren Kenny 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