Commit 045edee1 authored by Song Liu's avatar Song Liu Committed by Alexei Starovoitov
Browse files

bpf: Introduce KF_ARG_PTR_TO_CONST_STR 



Similar to ARG_PTR_TO_CONST_STR for BPF helpers, KF_ARG_PTR_TO_CONST_STR
specifies kfunc args that point to const strings. Annotation "__str" is
used to specify kfunc arg of type KF_ARG_PTR_TO_CONST_STR. Also, add
documentation for the "__str" annotation.

bpf_get_file_xattr() will be the first kfunc that uses this type.

Signed-off-by: default avatarSong Liu <song@kernel.org>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarVadim Fedorenko <vadim.fedorenko@linux.dev>
Link: https://lore.kernel.org/bpf/20231107045725.2278852-4-song@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 0b519407

Documentation/bpf/kfuncs.rst

+24 −0
Original line number Diff line number Diff line
@@ -135,6 +135,30 @@ Either way, the returned buffer is either NULL, or of size buffer_szk. Without t 
annotation, the verifier will reject the program if a null pointer is passed in with

a nonzero size.



2.2.5 __str Annotation

----------------------------

This annotation is used to indicate that the argument is a constant string.



An example is given below::



        __bpf_kfunc bpf_get_file_xattr(..., const char *name__str, ...)

        {

        ...

        }



In this case, ``bpf_get_file_xattr()`` can be called as::



        bpf_get_file_xattr(..., "xattr_name", ...);



Or::



        const char name[] = "xattr_name";  /* This need to be global */

        int BPF_PROG(...)

        {

                ...

                bpf_get_file_xattr(..., name, ...);

                ...

        }



.. _BPF_kfunc_nodef:

kernel/bpf/verifier.c

+19 −0
Original line number Diff line number Diff line
@@ -10810,6 +10810,11 @@ static bool is_kfunc_arg_nullable(const struct btf *btf, const struct btf_param 
	return __kfunc_param_match_suffix(btf, arg, "__nullable");

}









static bool is_kfunc_arg_const_str(const struct btf *btf, const struct btf_param *arg)









{









	return __kfunc_param_match_suffix(btf, arg, "__str");









}

















static bool is_kfunc_arg_scalar_with_name(const struct btf *btf,









					  const struct btf_param *arg,









					  const char *name)








@@ -10953,6 +10958,7 @@ enum kfunc_ptr_arg_type {







	KF_ARG_PTR_TO_RB_ROOT,









	KF_ARG_PTR_TO_RB_NODE,









	KF_ARG_PTR_TO_NULL,









	KF_ARG_PTR_TO_CONST_STR,









};

















enum special_kfunc_type {








@@ -11103,6 +11109,9 @@ get_kfunc_ptr_arg_type(struct bpf_verifier_env *env,







	if (is_kfunc_arg_rbtree_node(meta->btf, &args[argno]))









		return KF_ARG_PTR_TO_RB_NODE;

















	if (is_kfunc_arg_const_str(meta->btf, &args[argno]))









		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)) {









			verbose(env, "kernel function %s args#%d pointer type %s %s is not supported\n",








@@ -11734,6 +11743,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_







		case KF_ARG_PTR_TO_MEM_SIZE:









		case KF_ARG_PTR_TO_CALLBACK:









		case KF_ARG_PTR_TO_REFCOUNTED_KPTR:









		case KF_ARG_PTR_TO_CONST_STR:









			/* Trusted by default */









			break;









		default:








@@ -12005,6 +12015,15 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_







			meta->arg_btf = reg->btf;









			meta->arg_btf_id = reg->btf_id;









			break;









		case KF_ARG_PTR_TO_CONST_STR:









			if (reg->type != PTR_TO_MAP_VALUE) {









				verbose(env, "arg#%d doesn't point to a const string\n", i);









				return -EINVAL;









			}









			ret = check_reg_const_str(env, reg, regno);









			if (ret)









				return ret;









			break;









		}









	}