[PATCH v8 bpf-next 3/9] bpf: Introduce KF_ARG_PTR_TO_CONST_STR

Song Liu
2023-11-02T20:16:46Z

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>
---
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 238a8e08e781..2eb051ab9c70 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10656,6 +10656,11 @@ 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)
@@ -10799,6 +10804,7 @@ 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 {
@@ -10943,6 +10949,9 @@ 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",
@@ -11566,6 +11575,7 @@ 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:
@@ -11837,6 +11847,15 @@ 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