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Wed, 21 Oct 2020 21:09:53 +0000 From: Alexander Bulekov To: qemu-devel@nongnu.org Subject: [PATCH v6 12/16] fuzz: Add instructions for using generic-fuzz Date: Wed, 21 Oct 2020 17:09:18 -0400 Message-Id: <20201021210922.572955-13-alxndr@bu.edu> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20201021210922.572955-1-alxndr@bu.edu> References: <20201021210922.572955-1-alxndr@bu.edu> X-Originating-IP: [72.93.72.163] X-ClientProxiedBy: BL0PR0102CA0064.prod.exchangelabs.com (2603:10b6:208:25::41) To SN6PR03MB3871.namprd03.prod.outlook.com (2603:10b6:805:6d::32) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from stormtrooper.vrmnet (72.93.72.163) by BL0PR0102CA0064.prod.exchangelabs.com (2603:10b6:208:25::41) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3499.18 via Frontend Transport; Wed, 21 Oct 2020 21:09:52 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 03f08d27-8152-41f1-cb66-08d87605a76a X-MS-TrafficTypeDiagnostic: SN6PR03MB4045: X-MS-Exchange-Transport-Forked: True X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:9508; 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envelope-from=alxndr@bu.edu; helo=NAM04-CO1-obe.outbound.protection.outlook.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/10/21 17:10:05 X-ACL-Warn: Detected OS = Windows NT kernel [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, HK_RANDOM_ENVFROM=0.001, HK_RANDOM_FROM=0.454, MSGID_FROM_MTA_HEADER=0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no 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: Thomas Huth , Alexander Bulekov , f4bug@amsat.org, darren.kenny@oracle.com, bsd@redhat.com, stefanha@redhat.com, pbonzini@redhat.com, dimastep@yandex-team.ru Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Reviewed-by: Darren Kenny Signed-off-by: Alexander Bulekov --- docs/devel/fuzzing.txt | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) diff --git a/docs/devel/fuzzing.txt b/docs/devel/fuzzing.txt index 96d71c94d7..03585c1a9b 100644 --- a/docs/devel/fuzzing.txt +++ b/docs/devel/fuzzing.txt @@ -125,6 +125,45 @@ provided by libfuzzer. Libfuzzer passes a byte array and length. Commonly the fuzzer loops over the byte-array interpreting it as a list of qtest commands, addresses, or values. +== The Generic Fuzzer == +Writing a fuzz target can be a lot of effort (especially if a device driver has +not be built-out within libqos). Many devices can be fuzzed to some degree, +without any device-specific code, using the generic-fuzz target. + +The generic-fuzz target is capable of fuzzing devices over their PIO, MMIO, +and DMA input-spaces. To apply the generic-fuzz to a device, we need to define +two env-variables, at minimum: + +QEMU_FUZZ_ARGS= is the set of QEMU arguments used to configure a machine, with +the device attached. For example, if we want to fuzz the virtio-net device +attached to a pc-i440fx machine, we can specify: +QEMU_FUZZ_ARGS="-M pc -nodefaults -netdev user,id=user0 \ + -device virtio-net,netdev=user0" + +QEMU_FUZZ_OBJECTS= is a set of space-delimited strings used to identify the +MemoryRegions that will be fuzzed. These strings are compared against +MemoryRegion names and MemoryRegion owner names, to decide whether each +MemoryRegion should be fuzzed. These strings support globbing. For the +virtio-net example, we could use QEMU_FUZZ_OBJECTS= + * 'virtio-net' + * 'virtio*' + * 'virtio* pcspk' (Fuzz the virtio devices and the PC speaker...) + * '*' (Fuzz the whole machine) + +The "info mtree" and "info qom-tree" monitor commands can be especially useful +for identifying the MemoryRegion and Object names used for matching. + +As a generic rule-of-thumb, the more MemoryRegions/Devices we match, the greater +the input-space, and the smaller the probability of finding crashing inputs for +individual devices. As such, it is usually a good idea to limit the fuzzer to +only a few MemoryRegions. + +To ensure that these env variables have been configured correctly, we can use: + +./qemu-fuzz-i386 --fuzz-target=generic-fuzz -runs=0 + +The output should contain a complete list of matched MemoryRegions. + = Implementation Details = == The Fuzzer's Lifecycle ==