diff options
author | Alexander Bulekov <alxndr@bu.edu> | 2020-10-23 11:07:41 -0400 |
---|---|---|
committer | Thomas Huth <thuth@redhat.com> | 2020-10-26 09:53:53 +0100 |
commit | 2f2e036ca6e2c4d15841f6d29a17c2ae0961aca8 (patch) | |
tree | fe2dad56321cd5742959f25ba3020dbe8060daa3 /docs/devel | |
parent | cd3f0686ddf3cd18f307fb9f55f9cf21bf185bbf (diff) |
fuzz: Add instructions for using generic-fuzz
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Message-Id: <20201023150746.107063-13-alxndr@bu.edu>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Diffstat (limited to 'docs/devel')
-rw-r--r-- | docs/devel/fuzzing.txt | 39 |
1 files changed, 39 insertions, 0 deletions
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 == |