Re: [PATCH bpf-next v3 1/2] bpf: support bpf_get_func_arg() for BPF_TRACE_RAW_TP

On 2026/1/20 02:44, bot+bpf-ci@kernel.org wrote:

quoted

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index f73e08c223b5..64976009ba3c 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c

@@ -1734,11 +1734,11 @@ 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;
+		return &bpf_get_func_arg_proto;

Removing the bpf_prog_has_trampoline() check here allows all TRACING
program types to use bpf_get_func_arg(), not just RAW_TP and trampoline-
based types. In particular, BPF_TRACE_ITER programs can now use this
helper.

However, looking at do_misc_fixups() in verifier.c, the inline code
generation only handles BPF_TRACE_RAW_TP specially. For other non-
trampoline types like BPF_TRACE_ITER, the else branch generates:

    BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8)

This loads nr_args from ctx-8, but ITER programs use a different context
layout (e.g. struct bpf_iter__bpf_map_elem with meta, map, key, value
pointers). There is no nr_args at ctx-8 for ITER programs.

Would this cause ITER programs using bpf_get_func_arg() to read arbitrary
memory at ctx-8, potentially leaking kernel data or causing incorrect
bounds checks for subsequent argument access?

You are right. As Yonghong said, I missed the bpf_iter case, and it should
be skipped.

I'll fix it in the next version.

quoted

 	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;
+		return &bpf_get_func_arg_cnt_proto;

Same question applies here for bpf_get_func_arg_cnt() with ITER programs.

quoted

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 9de0ec0c3ed9..0b281b7c41eb 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c

@@ -23323,8 +23323,20 @@ 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) {
+			if (eatype == BPF_TRACE_RAW_TP) {
+				int nr_args = btf_type_vlen(prog->aux->attach_func_proto);
+
+				/*
+				 * skip first 'void *__data' argument in btf_trace_##name
+				 * typedef
+				 */
+				nr_args--;
+				/* Save nr_args to reg0 */
+				insn_buf[0] = BPF_MOV64_IMM(BPF_REG_0, nr_args);
+			} else {
+				/* Load nr_args from ctx - 8 */
+				insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1, -8);
+			}

This else branch now applies to BPF_TRACE_ITER as well, since the
trampoline check was removed in tracing_prog_func_proto(). Should the
condition be extended to also handle ITER, or should ITER be explicitly
blocked from using these helpers?

[ ... ]


---
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CI run summary: https://github.com/kernel-patches/bpf/actions/runs/21147849826