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bh=i/DGdtQQ1rUmbZ91UH2o/Fu6b9EvArbb0mGvRXoUJYc=; b=Oau0YtiBwa7bjhW0Zfs5QSqrZAJ7gmimt+7PNzkmiOZrRjPZBxoOaXwHdvtP0GvSVjrTjc Yz5LN53adudEJiualByYKeUpTSXIlCIrWqS7OmhzH/Qhjh/MxABcIG4bXu4cg7qlKyOTj5 KmY9+JMRDXQ5gvwsH3mhB92jDGLizFo= X-MC-Unique: 5wlDERFwNueVMz-1cwacPQ-1 From: Paolo Bonzini To: qemu-devel@nongnu.org Subject: [PULL 07/16] fuzz: add instructions for building reproducers Date: Tue, 16 Mar 2021 17:15:22 -0400 Message-Id: <20210316211531.1649909-8-pbonzini@redhat.com> In-Reply-To: <20210316211531.1649909-1-pbonzini@redhat.com> References: <20210316211531.1649909-1-pbonzini@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=pbonzini@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=216.205.24.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.25, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=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: Alexander Bulekov , Darren Kenny Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: pass (identity @redhat.com) Content-Type: text/plain; charset="utf-8" From: Alexander Bulekov We have several scripts that help build reproducers, but no documentation for how they should be used. Add some documentation Signed-off-by: Alexander Bulekov Reviewed-by: Darren Kenny Signed-off-by: Paolo Bonzini --- docs/devel/fuzzing.rst | 56 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 56 insertions(+) diff --git a/docs/devel/fuzzing.rst b/docs/devel/fuzzing.rst index 97797c4f8c..2749bb9bed 100644 --- a/docs/devel/fuzzing.rst +++ b/docs/devel/fuzzing.rst @@ -210,6 +210,62 @@ Build details: - The script responsible for building the fuzzers can be found in the QEMU source tree at ``scripts/oss-fuzz/build.sh`` =20 +Building Crash Reproducers +----------------------------------------- +When we find a crash, we should try to create an independent reproducer, t= hat +can be used on a non-fuzzer build of QEMU. This filters out any potential +false-positives, and improves the debugging experience for developers. +Here are the steps for building a reproducer for a crash found by the +generic-fuzz target. + +- Ensure the crash reproduces:: + + qemu-fuzz-i386 --fuzz-target... ./crash-... + +- Gather the QTest output for the crash:: + + QEMU_FUZZ_TIMEOUT=3D0 QTEST_LOG=3D1 FUZZ_SERIALIZE_QTEST=3D1 \ + qemu-fuzz-i386 --fuzz-target... ./crash-... &> /tmp/trace + +- Reorder and clean-up the resulting trace:: + + scripts/oss-fuzz/reorder_fuzzer_qtest_trace.py /tmp/trace > /tmp/repro= ducer + +- Get the arguments needed to start qemu, and provide a path to qemu:: + + less /tmp/trace # The args should be logged at the top of this file + export QEMU_ARGS=3D"-machine ..." + export QEMU_PATH=3D"path/to/qemu-system" + +- Ensure the crash reproduces in qemu-system:: + + $QEMU_PATH $QEMU_ARGS -qtest stdio < /tmp/reproducer + +- From the crash output, obtain some string that identifies the crash. This + can be a line in the stack-trace, for example:: + + export CRASH_TOKEN=3D"hw/usb/hcd-xhci.c:1865" + +- Minimize the reproducer:: + + scripts/oss-fuzz/minimize_qtest_trace.py -M1 -M2 \ + /tmp/reproducer /tmp/reproducer-minimized + +- Confirm that the minimized reproducer still crashes:: + + $QEMU_PATH $QEMU_ARGS -qtest stdio < /tmp/reproducer-minimized + +- Create a one-liner reproducer that can be sent over email:: + + ./scripts/oss-fuzz/output_reproducer.py -bash /tmp/reproducer-minimized + +- Output the C source code for a test case that will reproduce the bug:: + + ./scripts/oss-fuzz/output_reproducer.py -owner "John Smith "\ + -name "test_function_name" /tmp/reproducer-minimized + +- Report the bug and send a patch with the C reproducer upstream + Implementation Details / Fuzzer Lifecycle ----------------------------------------- =20 --=20 2.26.2