Signed-off-by: Alexander Bulekov <alx...@bu.edu> --- docs/devel/fuzzing.txt | 38 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+)
diff --git a/docs/devel/fuzzing.txt b/docs/devel/fuzzing.txt index 96d71c94d7..208b0c8360 100644 --- a/docs/devel/fuzzing.txt +++ b/docs/devel/fuzzing.txt @@ -125,6 +125,44 @@ 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 General 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 general-fuzz target. + +The general-fuzz target is capable of fuzzing devices over their PIO, MMIO, +and DMA input-spaces. To apply the general-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' +QEMU_FUZZ_OBJECTS='virtio*' +QEMU_FUZZ_OBJECTS='virtio* pcspk' # Fuzz the virtio-net device and the PC speaker... +QEMU_FUZZ_OBJECTS='*' # 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 general 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=general-fuzz -runs=0 + +The output should contain a complete list of matched MemoryRegions. + = Implementation Details = == The Fuzzer's Lifecycle == -- 2.28.0
