From patchwork Tue Jul 21 08:10:51 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Thomas Huth X-Patchwork-Id: 277677 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 72204C433E3 for ; Tue, 21 Jul 2020 08:14:10 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 4127C20720 for ; 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Tue, 21 Jul 2020 08:11:07 +0000 (UTC) Received: from thuth.com (ovpn-112-102.ams2.redhat.com [10.36.112.102]) by smtp.corp.redhat.com (Postfix) with ESMTP id 137CA2DE68; Tue, 21 Jul 2020 08:11:05 +0000 (UTC) From: Thomas Huth To: peter.maydell@linaro.org, qemu-devel@nongnu.org Subject: [PULL 06/10] docs/fuzz: add information about useful libFuzzer flags Date: Tue, 21 Jul 2020 10:10:51 +0200 Message-Id: <20200721081055.14073-7-thuth@redhat.com> In-Reply-To: <20200721081055.14073-1-thuth@redhat.com> References: <20200721081055.14073-1-thuth@redhat.com> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Received-SPF: pass client-ip=205.139.110.120; envelope-from=thuth@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/21 01:30:29 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, 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 Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" From: Alexander Bulekov Signed-off-by: Alexander Bulekov Message-Id: <20200706195534.14962-4-alxndr@bu.edu> Signed-off-by: Thomas Huth --- docs/devel/fuzzing.txt | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) diff --git a/docs/devel/fuzzing.txt b/docs/devel/fuzzing.txt index 12bf6aa0ca..6d18115239 100644 --- a/docs/devel/fuzzing.txt +++ b/docs/devel/fuzzing.txt @@ -48,6 +48,43 @@ Information about these is available by passing -help=1 Now the only thing left to do is wait for the fuzzer to trigger potential crashes. +== Useful libFuzzer flags == + +As mentioned above, libFuzzer accepts some arguments. Passing -help=1 will list +the available arguments. In particular, these arguments might be helpful: + +$CORPUS_DIR/ : Specify a directory as the last argument to libFuzzer. libFuzzer +stores each "interesting" input in this corpus directory. The next time you run +libFuzzer, it will read all of the inputs from the corpus, and continue fuzzing +from there. You can also specify multiple directories. libFuzzer loads existing +inputs from all specified directories, but will only write new ones to the +first one specified. + +-max_len=4096 : specify the maximum byte-length of the inputs libFuzzer will +generate. + +-close_fd_mask={1,2,3} : close, stderr, or both. Useful for targets that +trigger many debug/error messages, or create output on the serial console. + +-jobs=4 -workers=4 : These arguments configure libFuzzer to run 4 fuzzers in +parallel (4 fuzzing jobs in 4 worker processes). Alternatively, with only +-jobs=N, libFuzzer automatically spawns a number of workers less than or equal +to half the available CPU cores. Replace 4 with a number appropriate for your +machine. Make sure to specify a $CORPUS_DIR, which will allow the parallel +fuzzers to share information about the interesting inputs they find. + +-use_value_profile=1 : For each comparison operation, libFuzzer computes +(caller_pc&4095) | (popcnt(Arg1 ^ Arg2) << 12) and places this in the coverage +table. Useful for targets with "magic" constants. If Arg1 came from the fuzzer's +input and Arg2 is a magic constant, then each time the Hamming distance +between Arg1 and Arg2 decreases, libFuzzer adds the input to the corpus. + +-shrink=1 : Tries to make elements of the corpus "smaller". Might lead to +better coverage performance, depending on the target. + +Note that libFuzzer's exact behavior will depend on the version of +clang and libFuzzer used to build the device fuzzers. + == Adding a new fuzzer == Coverage over virtual devices can be improved by adding additional fuzzers. Fuzzers are kept in tests/qtest/fuzz/ and should be added to