From: Kaitao Cheng <[email protected]> KF_ARG_PTR_TO_LIST_NODE normally requires an owning reference (PTR_TO_BTF_ID | MEM_ALLOC and ref_obj_id). For bpf_list_add_impl's third argument (prev), allow a non-owning reference with ref_obj_id==0 so that the result of bpf_list_front() or bpf_list_back() can be passed as the insertion point. When prev is such a non-owning ref, skip the MEM_ALLOC/ref_obj_id checks and jump to the shared list-node processing. Owning refs (e.g. from pop + refcount_acquire) still pass the existing checks and reach the same label.
Add BTF suffix __nonown_allowed (is_kfunc_arg_nonown_allowed) and document it under kfuncs.rst. Signed-off-by: Kaitao Cheng <[email protected]> --- Documentation/bpf/kfuncs.rst | 20 +++++++++++++++++++- kernel/bpf/helpers.c | 4 ++-- kernel/bpf/verifier.c | 13 +++++++++++++ 3 files changed, 34 insertions(+), 3 deletions(-) diff --git a/Documentation/bpf/kfuncs.rst b/Documentation/bpf/kfuncs.rst index 75e6c078e0e7..6760c547dd32 100644 --- a/Documentation/bpf/kfuncs.rst +++ b/Documentation/bpf/kfuncs.rst @@ -207,7 +207,25 @@ Here, the buffer may be NULL. If the buffer is not NULL, it must be at least buffer__szk bytes in size. The kfunc is responsible for checking if the buffer is NULL before using it. -2.3.5 __str Annotation +2.3.5 __nonown_allowed Annotation +---------------------------------- + +This annotation is used to indicate that the parameter may be a non-owning reference. + +An example is given below:: + + __bpf_kfunc int bpf_list_add_impl(..., struct bpf_list_node + *prev__nonown_allowed, ...) + { + ... + } + +For the ``prev__nonown_allowed`` parameter (resolved as ``KF_ARG_PTR_TO_LIST_NODE``), +suffix ``__nonown_allowed`` retains the usual owning-pointer rules and also +permits a non-owning reference with no ref_obj_id (e.g. the return value of +bpf_list_front() / bpf_list_back()). + +2.3.6 __str Annotation ---------------------------- This annotation is used to indicate that the argument is a constant string. diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index 68c83a009275..743341aae5c0 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -2449,10 +2449,10 @@ __bpf_kfunc int bpf_list_push_back_impl(struct bpf_list_head *head, __bpf_kfunc int bpf_list_add_impl(struct bpf_list_head *head, struct bpf_list_node *new, - struct bpf_list_node *prev, + struct bpf_list_node *prev__nonown_allowed, void *meta__ign, u64 off) { - struct bpf_list_node_kern *n = (void *)new, *p = (void *)prev; + struct bpf_list_node_kern *n = (void *)new, *p = (void *)prev__nonown_allowed; struct btf_struct_meta *meta = meta__ign; struct list_head *prev_ptr = &p->list_head; diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 69dcf0105973..514a0aab93b8 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -12265,6 +12265,11 @@ static bool is_kfunc_arg_nullable(const struct btf *btf, const struct btf_param return btf_param_match_suffix(btf, arg, "__nullable"); } +static bool is_kfunc_arg_nonown_allowed(const struct btf *btf, const struct btf_param *arg) +{ + return btf_param_match_suffix(btf, arg, "__nonown_allowed"); +} + static bool is_kfunc_arg_const_str(const struct btf *btf, const struct btf_param *arg) { return btf_param_match_suffix(btf, arg, "__str"); @@ -13736,6 +13741,13 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ return ret; break; case KF_ARG_PTR_TO_LIST_NODE: + if (is_kfunc_arg_nonown_allowed(btf, &args[i]) && + type_is_non_owning_ref(reg->type) && !reg->ref_obj_id) { + /* Allow bpf_list_front/back return value as + * list_add_impl's third arg (R3). + */ + goto check_ok; + } if (reg->type != (PTR_TO_BTF_ID | MEM_ALLOC)) { verbose(env, "arg#%d expected pointer to allocated object\n", i); return -EINVAL; @@ -13744,6 +13756,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ verbose(env, "allocated object must be referenced\n"); return -EINVAL; } +check_ok: ret = process_kf_arg_ptr_to_list_node(env, reg, regno, meta); if (ret < 0) return ret; -- 2.50.1 (Apple Git-155)
