Re: [PATCH v12 bpf-next 3/9] bpf: Introduce KF_ARG_PTR_TO_CONST_STR

[Vadim Fedorenko <vadim.fedorenko@linux.dev>]

On 04/11/2023 00:13, Song Liu 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@kernel.org>
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
> ---
>   Documentation/bpf/kfuncs.rst | 24 ++++++++++++++++++++++++
>   kernel/bpf/verifier.c        | 19 +++++++++++++++++++
>   2 files changed, 43 insertions(+)
> 
> 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 618446006d5a..bf94ba50c6ee 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;
>   		}
>   	}
>   

Acked-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>

Alexei, Andrii, is it possible to apply patches 1-3? Looks like they
are ready to go and can unblock other work.