[PATCH RFC bpf-next 7/8] bpf: implement __aux kfunc argument suffix to fetch prog_aux

[Benjamin Tissoires]

This allows kfunc to request the prog_aux environment in their
implementation, to have access to the originated bpf_prog for example.

Signed-off-by: Benjamin Tissoires <bentiss@xxxxxxxxxx>

---

This is an RFC, and is not meant to be fully reviewed/applied as it is.
I'm posting this to show what I wanted to explain in
https://lore.kernel.org/bpf/mhkzkf4e23uvljtmwizwcxyuyat2tmfxn33xb4t7waafgmsa66@mcrzpj3b6ssx/
---
 kernel/bpf/verifier.c | 40 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 39 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 6fba9e2caa83..33b108db0025 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10909,6 +10909,11 @@ static bool is_kfunc_arg_sleepable_async_cb(const struct btf *btf, const struct
 	return btf_param_match_suffix(btf, arg, "__s_async");
 }
 
+static bool is_kfunc_arg_prog_aux(const struct btf *btf, const struct btf_param *arg)
+{
+	return btf_param_match_suffix(btf, arg, "__aux");
+}
+
 static bool is_kfunc_arg_scalar_with_name(const struct btf *btf,
 					  const struct btf_param *arg,
 					  const char *name)
@@ -11807,7 +11812,8 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 
 		t = btf_type_skip_modifiers(btf, args[i].type, NULL);
 
-		if (is_kfunc_arg_ignore(btf, &args[i]))
+		if (is_kfunc_arg_ignore(btf, &args[i]) ||
+		    is_kfunc_arg_prog_aux(btf, &args[i]))
 			continue;
 
 		if (btf_type_is_scalar(t)) {
@@ -19950,6 +19956,38 @@ static int fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 		insn_buf[1] = ld_addrs[1];
 		insn_buf[2] = *insn;
 		*cnt = 3;
+	} else {
+		struct bpf_kfunc_call_arg_meta meta;
+		struct bpf_insn kfunc_insn = *insn;
+		const struct btf_param *args;
+		u32 i, nargs, prog_aux_arg;
+		const char *func_name;
+		int ret;
+
+		/* imm might not have func_id, so create a fake insn with the expected args */
+		kfunc_insn.imm = desc->func_id;
+
+		ret = fetch_kfunc_meta(env, &kfunc_insn, &meta, &func_name);
+		if (ret == 0) {
+			args = (const struct btf_param *)(meta.func_proto + 1);
+			nargs = btf_type_vlen(meta.func_proto);
+			prog_aux_arg = nargs;
+
+			for (i = 0; i < nargs; i++) {
+				if (is_kfunc_arg_prog_aux(meta.btf, &args[i]))
+					prog_aux_arg = i;
+			}
+
+			if (prog_aux_arg < nargs) {
+				struct bpf_insn ld_addrs[2] = { BPF_LD_IMM64(BPF_REG_1 + prog_aux_arg,
+								(long)env->prog->aux) };
+
+				insn_buf[0] = ld_addrs[0];
+				insn_buf[1] = ld_addrs[1];
+				insn_buf[2] = *insn;
+				*cnt = 3;
+			}
+		}
 	}
 	return 0;
 }

-- 
2.44.0