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bpf: Introduce KF_ARG_PTR_TO_CONST_STR

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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>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Link: https://lore.kernel.org/bpf/20231107045725.2278852-4-song@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Song Liu 2023-11-06 20:57:25 -08:00 committed by Alexei Starovoitov
parent 0b51940729
commit 045edee19d
2 changed files with 43 additions and 0 deletions
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24
Documentation/bpf/kfuncs.rst
View file

@ -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:

19
kernel/bpf/verifier.c
View file

@ -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;
}
}