selftests/bpf: Add verifier test for d_path helper

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>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200825192124.710397-13-jolsa@kernel.org

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 +985,24 @@ 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 < 0) {
+			printf("FAIL\nFailed to find BTF ID for '%s'!\n",
+				test->kfunc);
+			(*errors)++;
+			return;
+		}
+	}
+
 	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 &&
+	    !bpf_probe_prog_type(prog_type, 0)) {
 		printf("SKIP (unsupported program type %d)\n", prog_type);
 		skips++;
 		goto close_fds;

tools/testing/selftests/bpf/verifier/d_path.c

@@ -0,0 +1,37 @@
+{
+	"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(),
+	},
+	.result = ACCEPT,
+	.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",
+},