[PATCH bpf-next v2 2/6] bpf: Introduce css_task open-coded iterator kfuncs

Chuyi Zhou
2023-09-12T07:02:07Z

This patch adds kfuncs bpf_iter_css_task_{new,next,destroy} which allow
creation and manipulation of struct bpf_iter_css_task in open-coded
iterator style. These kfuncs actually wrapps css_task_iter_{start,next,
end}. BPF programs can use these kfuncs through bpf_for_each macro for
iteration of all tasks under a css.

css_task_iter_*() would try to get the global spin-lock *css_set_lock*, so
the bpf side has to be careful in where it allows to use this iter.
Currently we only allow it in bpf_lsm and bpf iter-s.

Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com>
---
include/uapi/linux/bpf.h | 4 +++
kernel/bpf/helpers.c | 3 +++
kernel/bpf/task_iter.c | 48 ++++++++++++++++++++++++++++++++++
kernel/bpf/verifier.c | 23 ++++++++++++++++
tools/include/uapi/linux/bpf.h | 4 +++
tools/lib/bpf/bpf_helpers.h | 7 +++++
6 files changed, 89 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 73b155e52204..de02c0971428 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -7318,4 +7318,8 @@ struct bpf_iter_num {
__u64 __opaque[1];
} __attribute__((aligned(8)));

+struct bpf_iter_css_task {
+ __u64 __opaque[1];
+} __attribute__((aligned(8)));
+
#endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index b0a9834f1051..d6a16becfbb9 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2504,6 +2504,9 @@ BTF_ID_FLAGS(func, bpf_dynptr_slice_rdwr, KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_iter_num_new, KF_ITER_NEW)
BTF_ID_FLAGS(func, bpf_iter_num_next, KF_ITER_NEXT | KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_iter_num_destroy, KF_ITER_DESTROY)
+BTF_ID_FLAGS(func, bpf_iter_css_task_new, KF_ITER_NEW)
+BTF_ID_FLAGS(func, bpf_iter_css_task_next, KF_ITER_NEXT | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_iter_css_task_destroy, KF_ITER_DESTROY)
BTF_ID_FLAGS(func, bpf_dynptr_adjust)
BTF_ID_FLAGS(func, bpf_dynptr_is_null)
BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly)
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index 7473068ed313..d8539cc05ffd 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -803,6 +803,54 @@ const struct bpf_func_proto bpf_find_vma_proto = {
.arg5_type = ARG_ANYTHING,
};

+struct bpf_iter_css_task_kern {
+ struct css_task_iter *css_it;
+} __attribute__((aligned(8)));
+
+__bpf_kfunc int bpf_iter_css_task_new(struct bpf_iter_css_task *it,
+ struct cgroup_subsys_state *css, unsigned int flags)
+{
+ struct bpf_iter_css_task_kern *kit = (void *)it;
+
+ BUILD_BUG_ON(sizeof(struct bpf_iter_css_task_kern) != sizeof(struct bpf_iter_css_task));
+ BUILD_BUG_ON(__alignof__(struct bpf_iter_css_task_kern) !=
+ __alignof__(struct bpf_iter_css_task));
+
+ switch (flags) {
+ case CSS_TASK_ITER_PROCS | CSS_TASK_ITER_THREADED:
+ case CSS_TASK_ITER_PROCS:
+ case 0:
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ kit->css_it = kzalloc(sizeof(struct css_task_iter), GFP_KERNEL);
+ if (!kit->css_it)
+ return -ENOMEM;
+ css_task_iter_start(css, flags, kit->css_it);
+ return 0;
+}
+
+__bpf_kfunc struct task_struct *bpf_iter_css_task_next(struct bpf_iter_css_task *it)
+{
+ struct bpf_iter_css_task_kern *kit = (void *)it;
+
+ if (!kit->css_it)
+ return NULL;
+ return css_task_iter_next(kit->css_it);
+}
+
+__bpf_kfunc void bpf_iter_css_task_destroy(struct bpf_iter_css_task *it)
+{
+ struct bpf_iter_css_task_kern *kit = (void *)it;
+
+ if (!kit->css_it)
+ return;
+ css_task_iter_end(kit->css_it);
+ kfree(kit->css_it);
+}
+
DEFINE_PER_CPU(struct mmap_unlock_irq_work, mmap_unlock_work);

static void do_mmap_read_unlock(struct irq_work *entry)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index dbba2b806017..2367483bf4c2 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10332,6 +10332,7 @@ enum special_kfunc_type {
KF_bpf_dynptr_clone,
KF_bpf_percpu_obj_new_impl,
KF_bpf_percpu_obj_drop_impl,
+ KF_bpf_iter_css_task_new,
};

BTF_SET_START(special_kfunc_set)
@@ -10354,6 +10355,7 @@ BTF_ID(func, bpf_dynptr_slice_rdwr)
BTF_ID(func, bpf_dynptr_clone)
BTF_ID(func, bpf_percpu_obj_new_impl)
BTF_ID(func, bpf_percpu_obj_drop_impl)
+BTF_ID(func, bpf_iter_css_task_new)
BTF_SET_END(special_kfunc_set)

BTF_ID_LIST(special_kfunc_list)
@@ -10378,6 +10380,7 @@ BTF_ID(func, bpf_dynptr_slice_rdwr)
BTF_ID(func, bpf_dynptr_clone)
BTF_ID(func, bpf_percpu_obj_new_impl)
BTF_ID(func, bpf_percpu_obj_drop_impl)
+BTF_ID(func, bpf_iter_css_task_new)

static bool is_kfunc_ret_null(struct bpf_kfunc_call_arg_meta *meta)
{
@@ -10902,6 +10905,20 @@ static int process_kf_arg_ptr_to_rbtree_node(struct bpf_verifier_env *env,
&meta->arg_rbtree_root.field);
}

+static bool check_css_task_iter_allowlist(struct bpf_verifier_env *env)
+{
+ enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
+
+ switch (prog_type) {
+ case BPF_PROG_TYPE_LSM:
+ return true;
+ case BPF_TRACE_ITER:
+ return env->prog->aux->sleepable;
+ default:
+ return false;
+ }
+}
+
static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_arg_meta *meta,
int insn_idx)
{
@@ -11152,6 +11169,12 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
break;
}
case KF_ARG_PTR_TO_ITER:
+ if (meta->func_id == special_kfunc_list[KF_bpf_iter_css_task_new]) {
+ if (!check_css_task_iter_allowlist(env)) {
+ verbose(env, "css_task_iter is only allowed in bpf_lsm and bpf iter-s\n");
+ return -EINVAL;
+ }
+ }
ret = process_iter_arg(env, regno, insn_idx, meta);
if (ret < 0)
return ret;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 73b155e52204..de02c0971428 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -7318,4 +7318,8 @@ struct bpf_iter_num {
__u64 __opaque[1];
} __attribute__((aligned(8)));

+struct bpf_iter_css_task {
+ __u64 __opaque[1];
+} __attribute__((aligned(8)));
+
#endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
index 77ceea575dc7..f48723c6c593 100644
--- a/tools/lib/bpf/bpf_helpers.h
+++ b/tools/lib/bpf/bpf_helpers.h
@@ -303,6 +303,13 @@ extern int bpf_iter_num_new(struct bpf_iter_num *it, int start, int end) __weak
extern int *bpf_iter_num_next(struct bpf_iter_num *it) __weak __ksym;
extern void bpf_iter_num_destroy(struct bpf_iter_num *it) __weak __ksym;

+struct bpf_iter_css_task;
+struct cgroup_subsys_state;
+extern int bpf_iter_css_task_new(struct bpf_iter_css_task *it,
+ struct cgroup_subsys_state *css, unsigned int flags) __weak __ksym;
+extern struct task_struct *bpf_iter_css_task_next(struct bpf_iter_css_task *it) __weak __ksym;
+extern void bpf_iter_css_task_destroy(struct bpf_iter_css_task *it) __weak __ksym;
+
#ifndef bpf_for_each
/* bpf_for_each(iter_type, cur_elem, args...) provides generic construct for
* using BPF open-coded iterators without having to write mundane explicit
--
2.20.1