[PATCH bpf-next v5 1/2] bpf: support bpf_get_func_arg() for BPF_TRACE_RAW_TP

[Menglong Dong <menglong8.dong@gmail.com>]

For now, bpf_get_func_arg() and bpf_get_func_arg_cnt() is not supported by
the BPF_TRACE_RAW_TP, which is not convenient to get the argument of the
tracepoint, especially for the case that the position of the arguments in
a tracepoint can change.

The target tracepoint BTF type id is specified during loading time,
therefore we can get the function argument count from the function
prototype instead of the stack.

Signed-off-by: Menglong Dong <dongml2@chinatelecom.cn>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
---
v5:
- some format adjustment

v4:
- fix the error of using bpf_get_func_arg() for BPF_TRACE_ITER

v3:
- remove unnecessary NULL checking for prog->aux->attach_func_proto

v2:
- for nr_args, skip first 'void *__data' argument in btf_trace_##name
  typedef
---
 kernel/bpf/verifier.c    | 22 ++++++++++++++++++----
 kernel/trace/bpf_trace.c | 10 ++++++++--
 2 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9de0ec0c3ed9..c3f8870ac5dc 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -23323,8 +23323,15 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 		/* Implement bpf_get_func_arg inline. */
 		if (prog_type == BPF_PROG_TYPE_TRACING &&
 		    insn->imm == BPF_FUNC_get_func_arg) {
-			/* Load nr_args from ctx - 8 */
-			insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
+			if (eatype == BPF_TRACE_RAW_TP) {
+				int nr_args = btf_type_vlen(prog->aux->attach_func_proto);
+
+				/* skip 'void *__data' in btf_trace_##name() and save to reg0 */
+				insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, nr_args - 1);
+			} else {
+				/* Load nr_args from ctx - 8 */
+				insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
+			}
 			insn_buf[1] = BPF_JMP32_REG(BPF_JGE, BPF_REG_2, BPF_REG_0, 6);
 			insn_buf[2] = BPF_ALU64_IMM(BPF_LSH, BPF_REG_2, 3);
 			insn_buf[3] = BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_1);
@@ -23376,8 +23383,15 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 		/* Implement get_func_arg_cnt inline. */
 		if (prog_type == BPF_PROG_TYPE_TRACING &&
 		    insn->imm == BPF_FUNC_get_func_arg_cnt) {
-			/* Load nr_args from ctx - 8 */
-			insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
+			if (eatype == BPF_TRACE_RAW_TP) {
+				int nr_args = btf_type_vlen(prog->aux->attach_func_proto);
+
+				/* skip 'void *__data' in btf_trace_##name() and save to reg0 */
+				insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, nr_args - 1);
+			} else {
+				/* Load nr_args from ctx - 8 */
+				insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
+			}
 
 			new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, 1);
 			if (!new_prog)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index f73e08c223b5..73c8f92c5d65 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1734,11 +1734,17 @@ tracing_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 	case BPF_FUNC_d_path:
 		return &bpf_d_path_proto;
 	case BPF_FUNC_get_func_arg:
-		return bpf_prog_has_trampoline(prog) ? &bpf_get_func_arg_proto : NULL;
+		if (bpf_prog_has_trampoline(prog) ||
+		    prog->expected_attach_type == BPF_TRACE_RAW_TP)
+			return &bpf_get_func_arg_proto;
+		return NULL;
 	case BPF_FUNC_get_func_ret:
 		return bpf_prog_has_trampoline(prog) ? &bpf_get_func_ret_proto : NULL;
 	case BPF_FUNC_get_func_arg_cnt:
-		return bpf_prog_has_trampoline(prog) ? &bpf_get_func_arg_cnt_proto : NULL;
+		if (bpf_prog_has_trampoline(prog) ||
+		    prog->expected_attach_type == BPF_TRACE_RAW_TP)
+			return &bpf_get_func_arg_cnt_proto;
+		return NULL;
 	case BPF_FUNC_get_attach_cookie:
 		if (prog->type == BPF_PROG_TYPE_TRACING &&
 		    prog->expected_attach_type == BPF_TRACE_RAW_TP)
-- 
2.52.0