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Tue, 12 Jan 2021 16:59:15 +0000 Subject: Re: [PATCH 2/2] selftests/bpf: add verifier test for PTR_TO_MEM spill To: Daniel Borkmann , Gilad Reti , KP Singh CC: bpf , Shuah Khan , Alexei Starovoitov , Andrii Nakryiko , Martin KaFai Lau , Song Liu , John Fastabend , , Networking , open list References: <20210112091545.10535-1-gilad.reti@gmail.com> <60034a79-573f-125c-76b0-17e04941a155@iogearbox.net> From: Yonghong Song Message-ID: Date: Tue, 12 Jan 2021 08:59:12 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 In-Reply-To: <60034a79-573f-125c-76b0-17e04941a155@iogearbox.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US X-Originating-IP: [2620:10d:c090:400::5:3e3] X-ClientProxiedBy: MW4PR04CA0171.namprd04.prod.outlook.com (2603:10b6:303:85::26) To BYAPR15MB4088.namprd15.prod.outlook.com (2603:10b6:a02:c3::18) X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2620:10d:c085:21e1::190b] (2620:10d:c090:400::5:3e3) by MW4PR04CA0171.namprd04.prod.outlook.com (2603:10b6:303:85::26) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3742.6 via Frontend Transport; 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You can make the following change to force the return value ("sample" here) of bpf_ringbuf_reserve() to spill on the stack. diff --git a/tools/testing/selftests/bpf/progs/test_ringbuf.c b/tools/testing/selftests/bpf/progs/test_ringbuf.c index 8ba9959b036b..011521170856 100644 --- a/tools/testing/selftests/bpf/progs/test_ringbuf.c +++ b/tools/testing/selftests/bpf/progs/test_ringbuf.c @@ -40,7 +40,7 @@ SEC("tp/syscalls/sys_enter_getpgid") int test_ringbuf(void *ctx) { int cur_pid = bpf_get_current_pid_tgid() >> 32; - struct sample *sample; + struct sample * volatile sample; int zero = 0; if (cur_pid != pid) This change will cause verifier failure without Patch #1. > >> It may be possible, but from what I understood from Daniel's comment here >> >> https://lore.kernel.org/bpf/17629073-4fab-a922-ecc3-25b019960f44@iogearbox.net/ >> >> >> the test should be a part of the verifier tests (which is reasonable >> to me since it is >> a verifier bugfix) > > Yeah, the test_verifier case as you have is definitely the most straight > forward way to add coverage in this case.