Re: [PATCH 10/11] selftests/bpf: Add verifier test for d_path helper

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Jiri Olsa <jolsa@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
	Martin KaFai Lau <kafai@fb.com>, David Miller <davem@redhat.com>,
	John Fastabend <john.fastabend@gmail.com>,
	Wenbo Zhang <ethercflow@gmail.com>,
	KP Singh <kpsingh@chromium.org>, Andrii Nakryiko <andriin@fb.com>,
	Brendan Gregg <bgregg@netflix.com>,
	Florent Revest <revest@chromium.org>,
	Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH 10/11] selftests/bpf: Add verifier test for d_path helper
Date: Thu, 18 Jun 2020 21:38:56 -0700	[thread overview]
Message-ID: <CAEf4BzYr6hwS5-XKAJt-QEyPiofNvj2M1WA_B-F29QCFoZU2jw@mail.gmail.com> (raw)
In-Reply-To: <20200616100512.2168860-11-jolsa@kernel.org>

On Tue, Jun 16, 2020 at 3:06 AM Jiri Olsa <jolsa@kernel.org> wrote:
>
> Adding verifier test for attaching tracing program and
> calling d_path helper from within and testing that it's
> allowed for dentry_open function and denied for 'd_path'
> function with appropriate error.
>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>  tools/testing/selftests/bpf/test_verifier.c   | 13 ++++++-
>  tools/testing/selftests/bpf/verifier/d_path.c | 38 +++++++++++++++++++
>  2 files changed, 50 insertions(+), 1 deletion(-)
>  create mode 100644 tools/testing/selftests/bpf/verifier/d_path.c
>
> diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> index 78a6bae56ea6..3cce3dc766a2 100644
> --- a/tools/testing/selftests/bpf/test_verifier.c
> +++ b/tools/testing/selftests/bpf/test_verifier.c
> @@ -114,6 +114,7 @@ struct bpf_test {
>                 bpf_testdata_struct_t retvals[MAX_TEST_RUNS];
>         };
>         enum bpf_attach_type expected_attach_type;
> +       const char *kfunc;
>  };
>
>  /* Note we want this to be 64 bit aligned so that the end of our array is
> @@ -984,8 +985,18 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
>                 attr.log_level = 4;
>         attr.prog_flags = pflags;
>
> +       if (prog_type == BPF_PROG_TYPE_TRACING && test->kfunc) {
> +               attr.attach_btf_id = libbpf_find_vmlinux_btf_id(test->kfunc,
> +                                               attr.expected_attach_type);

if (!attr.attach_btf_id)
  emit more meaningful error, than later during load?

> +       }
> +
>         fd_prog = bpf_load_program_xattr(&attr, bpf_vlog, sizeof(bpf_vlog));
> -       if (fd_prog < 0 && !bpf_probe_prog_type(prog_type, 0)) {
> +
> +       /* BPF_PROG_TYPE_TRACING requires more setup and
> +        * bpf_probe_prog_type won't give correct answer
> +        */
> +       if (fd_prog < 0 && (prog_type != BPF_PROG_TYPE_TRACING) &&

nit: () are redundant

> +           !bpf_probe_prog_type(prog_type, 0)) {
>                 printf("SKIP (unsupported program type %d)\n", prog_type);
>                 skips++;
>                 goto close_fds;
> diff --git a/tools/testing/selftests/bpf/verifier/d_path.c b/tools/testing/selftests/bpf/verifier/d_path.c
> new file mode 100644
> index 000000000000..e08181abc056
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/verifier/d_path.c
> @@ -0,0 +1,38 @@
> +{
> +       "d_path accept",
> +       .insns = {
> +       BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_1, 0),
> +       BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
> +       BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
> +       BPF_MOV64_IMM(BPF_REG_6, 0),
> +       BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_6, 0),
> +       BPF_LD_IMM64(BPF_REG_3, 8),
> +       BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_d_path),
> +       BPF_MOV64_IMM(BPF_REG_0, 0),
> +       BPF_EXIT_INSN(),
> +       },
> +       .errstr = "R0 max value is outside of the array range",
> +       .result = ACCEPT,

accept with error string expected?

> +       .prog_type = BPF_PROG_TYPE_TRACING,
> +       .expected_attach_type = BPF_TRACE_FENTRY,
> +       .kfunc = "dentry_open",
> +},
> +{
> +       "d_path reject",
> +       .insns = {
> +       BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_1, 0),
> +       BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
> +       BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
> +       BPF_MOV64_IMM(BPF_REG_6, 0),
> +       BPF_STX_MEM(BPF_DW, BPF_REG_2, BPF_REG_6, 0),
> +       BPF_LD_IMM64(BPF_REG_3, 8),
> +       BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_d_path),
> +       BPF_MOV64_IMM(BPF_REG_0, 0),
> +       BPF_EXIT_INSN(),
> +       },
> +       .errstr = "helper call is not allowed in probe",
> +       .result = REJECT,
> +       .prog_type = BPF_PROG_TYPE_TRACING,
> +       .expected_attach_type = BPF_TRACE_FENTRY,
> +       .kfunc = "d_path",
> +},
> --
> 2.25.4
>