On Fri, Nov 3, 2023 at 2:46 PM Song Liu <song@xxxxxxxxxx> wrote:
>
> 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: Song Liu <song@xxxxxxxxxx>
> ---
> Documentation/bpf/kfuncs.rst | 24 ++++++++++++++++++++++++
> kernel/bpf/verifier.c | 19 +++++++++++++++++++
> 2 files changed, 43 insertions(+)
>
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst
> index 0d2647fb358d..bfe065f7e23c 100644
> --- a/Documentation/bpf/kfuncs.rst
> +++ b/Documentation/bpf/kfuncs.rst
> @@ -137,6 +137,30 @@ 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:
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index fefe3eafccb9..6d382f20674d 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -10803,6 +10803,11 @@ 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)
> @@ -10946,6 +10951,7 @@ 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 {
> @@ -11090,6 +11096,9 @@ 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",
> @@ -11713,6 +11722,7 @@ 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:
> @@ -11984,6 +11994,15 @@ 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;
> }
> }
>
> --
> 2.34.1
>
