On Tue, 14 Feb 2023 at 12:59, Laurent Vivier <lviv...@redhat.com> wrote: > > On 2/14/23 17:08, Philippe Mathieu-Daudé wrote: > > On 14/2/23 16:38, Stefan Hajnoczi wrote: > >> On Sat, Feb 04, 2023 at 11:29:41PM -0500, Alexander Bulekov wrote: > >>> Hello, > >>> This series removes fork-based fuzzing. > >>> How does fork-based fuzzing work? > >>> * A single parent process initializes QEMU > >>> * We identify the devices we wish to fuzz (fuzzer-dependent) > >>> * Use QTest to PCI enumerate the devices > >>> * After that we start a fork-server which forks the process and executes > >>> fuzzer inputs inside the disposable children. > >>> > >>> In a normal fuzzing process, everything happens in a single process. > >>> > >>> Pros of fork-based fuzzing: > >>> * We only need to do common configuration once (e.g. PCI enumeration). > >>> * Fork provides a strong guarantee that fuzzer inputs will not > >>> interfere with > >>> each-other > >>> * The fuzzing process can continue even after a child-process crashes > >>> * We can apply our-own timers to child-processes to exit slow inputs, > >>> early > >>> > >>> Cons of fork-based fuzzing: > >>> * Fork-based fuzzing is not supported by libfuzzer. We had to build our > >>> own > >>> fork-server and rely on tricks using linker-scripts and shared-memory > >>> to > >>> support fuzzing. ( > >>> https://physics.bu.edu/~alxndr/libfuzzer-forkserver/ ) > >>> * Fork-based fuzzing is currently the main blocker preventing us from > >>> enabling > >>> other fuzzers such as AFL++ on OSS-Fuzz > >>> * Fork-based fuzzing may be a reason why coverage-builds are failing on > >>> OSS-Fuzz. Coverage is an important fuzzing metric which would allow > >>> us to > >>> find parts of the code that are not well-covered. > >>> * Fork-based fuzzing has high overhead. fork() is an expensive > >>> system-call, > >>> especially for processes running ASAN (with large/complex) VMA > >>> layouts. > >>> * Fork prevents us from effectively fuzzing devices that rely on > >>> threads (e.g. qxl). > >>> > >>> These patches remove fork-based fuzzing and replace it with reboot-based > >>> fuzzing for most cases. Misc notes about this change: > >>> * libfuzzer appears to be no longer in active development. As such, the > >>> current implementation of fork-based fuzzing (while having some nice > >>> advantages) is likely to hold us back in the future. If these changes > >>> are approved and appear to run successfully on OSS-Fuzz, we should be > >>> able to easily experiment with other fuzzing engines (AFL++). > >>> * Some device do not completely reset their state. This can lead to > >>> non-reproducible crashes. However, in my local tests, most crashes > >>> were reproducible. OSS-Fuzz shouldn't send us reports unless it can > >>> consistently reproduce a crash. > >>> * In theory, the corpus-format should not change, so the existing > >>> corpus-inputs on OSS-Fuzz will transfer to the new reset()-able > >>> fuzzers. > >>> * Each fuzzing process will now exit after a single crash is found. To > >>> continue the fuzzing process, use libfuzzer flags such as -jobs=-1 > >>> * We no long control input-timeouts (those are handled by libfuzzer). > >>> Since timeouts on oss-fuzz can be many seconds long, I added a limit > >>> on the number of DMA bytes written. > >>> > >>> Alexander Bulekov (10): > >>> hw/sparse-mem: clear memory on reset > >>> fuzz: add fuzz_reboot API > >>> fuzz/generic-fuzz: use reboots instead of forks to reset state > >>> fuzz/generic-fuzz: add a limit on DMA bytes written > >>> fuzz/virtio-scsi: remove fork-based fuzzer > >>> fuzz/virtio-net: remove fork-based fuzzer > >>> fuzz/virtio-blk: remove fork-based fuzzer > >>> fuzz/i440fx: remove fork-based fuzzer > >>> fuzz: remove fork-fuzzing scaffolding > >>> docs/fuzz: remove mentions of fork-based fuzzing > >>> > >>> docs/devel/fuzzing.rst | 22 +----- > >>> hw/mem/sparse-mem.c | 13 +++- > >>> meson.build | 4 - > >>> tests/qtest/fuzz/fork_fuzz.c | 41 ---------- > >>> tests/qtest/fuzz/fork_fuzz.h | 23 ------ > >>> tests/qtest/fuzz/fork_fuzz.ld | 56 -------------- > >>> tests/qtest/fuzz/fuzz.c | 6 ++ > >>> tests/qtest/fuzz/fuzz.h | 2 +- > >>> tests/qtest/fuzz/generic_fuzz.c | 111 +++++++--------------------- > >>> tests/qtest/fuzz/i440fx_fuzz.c | 27 +------ > >>> tests/qtest/fuzz/meson.build | 6 +- > >>> tests/qtest/fuzz/virtio_blk_fuzz.c | 51 ++----------- > >>> tests/qtest/fuzz/virtio_net_fuzz.c | 54 ++------------ > >>> tests/qtest/fuzz/virtio_scsi_fuzz.c | 51 ++----------- > >>> 14 files changed, 72 insertions(+), 395 deletions(-) > >>> delete mode 100644 tests/qtest/fuzz/fork_fuzz.c > >>> delete mode 100644 tests/qtest/fuzz/fork_fuzz.h > >>> delete mode 100644 tests/qtest/fuzz/fork_fuzz.ld > >>> > >>> -- > >>> 2.39.0 > >>> > >> > >> Whose tree should this go through? Laurent's qtest tree? > > > > Do you mean Thomas? > > > > $ git shortlog -cs tests/qtest/fuzz | sort -rn > > 32 Thomas Huth > > 26 Paolo Bonzini > > 19 Stefan Hajnoczi > > 6 Markus Armbruster > > 5 Alexander Bulekov > > 4 Marc-André Lureau > > 3 Peter Maydell > > 2 Laurent Vivier > > 1 Michael S. Tsirkin > > 1 Gerd Hoffmann > > > > In doubt, cc'ing both :) > > Yes, Thomas is the real maintainer.
Want to update the ./MAINTAINERS file? That's where I found your name. Thomas is only listed as a reviewer. Stefan
