[PATCH v2 bpf-next 02/20] bpf: Recognize '__map' suffix in kfunc arguments

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

From: Alexei Starovoitov <ast@kernel.org>

Recognize 'void *p__map' kfunc argument as 'struct bpf_map *p__map'.
It allows kfunc to have 'void *' argument for maps, since bpf progs
will call them as:
struct {
        __uint(type, BPF_MAP_TYPE_ARENA);
	...
} arena SEC(".maps");

bpf_kfunc_with_map(... &arena ...);

Underneath libbpf will load CONST_PTR_TO_MAP into the register via ld_imm64 insn.
If kfunc was defined with 'struct bpf_map *' it would pass
the verifier, but bpf prog would need to use '(void *)&arena'.
Which is not clean.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 kernel/bpf/verifier.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d9c2dbb3939f..db569ce89fb1 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10741,6 +10741,11 @@ static bool is_kfunc_arg_ignore(const struct btf *btf, const struct btf_param *a
 	return __kfunc_param_match_suffix(btf, arg, "__ign");
 }
 
+static bool is_kfunc_arg_map(const struct btf *btf, const struct btf_param *arg)
+{
+	return __kfunc_param_match_suffix(btf, arg, "__map");
+}
+
 static bool is_kfunc_arg_alloc_obj(const struct btf *btf, const struct btf_param *arg)
 {
 	return __kfunc_param_match_suffix(btf, arg, "__alloc");
@@ -11064,7 +11069,7 @@ get_kfunc_ptr_arg_type(struct bpf_verifier_env *env,
 		return KF_ARG_PTR_TO_CONST_STR;
 
 	if ((base_type(reg->type) == PTR_TO_BTF_ID || reg2btf_ids[base_type(reg->type)])) {
-		if (!btf_type_is_struct(ref_t)) {
+		if (!btf_type_is_struct(ref_t) && !btf_type_is_void(ref_t)) {
 			verbose(env, "kernel function %s args#%d pointer type %s %s is not supported\n",
 				meta->func_name, argno, btf_type_str(ref_t), ref_tname);
 			return -EINVAL;
@@ -11660,6 +11665,13 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 		if (kf_arg_type < 0)
 			return kf_arg_type;
 
+		if (is_kfunc_arg_map(btf, &args[i])) {
+			/* If argument has '__map' suffix expect 'struct bpf_map *' */
+			ref_id = *reg2btf_ids[CONST_PTR_TO_MAP];
+			ref_t = btf_type_by_id(btf_vmlinux, ref_id);
+			ref_tname = btf_name_by_offset(btf, ref_t->name_off);
+		}
+
 		switch (kf_arg_type) {
 		case KF_ARG_PTR_TO_NULL:
 			continue;
-- 
2.34.1