On Sun, Aug 27, 2023 at 12:21 AM Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx> wrote:
>
> This patch adds kfuncs bpf_iter_process_{new,next,destroy} which allow
> creation and manipulation of struct bpf_iter_process in open-coded iterator
> style. BPF programs can use these kfuncs or through bpf_for_each macro to
> iterate all processes in the system.
>
> Signed-off-by: Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx>
> ---
> include/uapi/linux/bpf.h | 4 ++++
> kernel/bpf/helpers.c | 3 +++
> kernel/bpf/task_iter.c | 31 +++++++++++++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 4 ++++
> tools/lib/bpf/bpf_helpers.h | 5 +++++
> 5 files changed, 47 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 2a6e9b99564b..cfbd527e3733 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -7199,4 +7199,8 @@ struct bpf_iter_css_task {
> __u64 __opaque[1];
> } __attribute__((aligned(8)));
>
> +struct bpf_iter_process {
> + __u64 __opaque[1];
> +} __attribute__((aligned(8)));
> +
> #endif /* _UAPI__LINUX_BPF_H__ */
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index cf113ad24837..81a2005edc26 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -2458,6 +2458,9 @@ 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_iter_process_new, KF_ITER_NEW)
> +BTF_ID_FLAGS(func, bpf_iter_process_next, KF_ITER_NEXT | KF_RET_NULL)
> +BTF_ID_FLAGS(func, bpf_iter_process_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 b1bdba40b684..a6717a76c1e0 100644
> --- a/kernel/bpf/task_iter.c
> +++ b/kernel/bpf/task_iter.c
> @@ -862,6 +862,37 @@ __bpf_kfunc void bpf_iter_css_task_destroy(struct bpf_iter_css_task *it)
> kfree(kit->css_it);
> }
>
> +struct bpf_iter_process_kern {
> + struct task_struct *tsk;
> +} __attribute__((aligned(8)));
> +
> +__bpf_kfunc int bpf_iter_process_new(struct bpf_iter_process *it)
> +{
> + struct bpf_iter_process_kern *kit = (void *)it;
> +
> + BUILD_BUG_ON(sizeof(struct bpf_iter_process_kern) != sizeof(struct bpf_iter_process));
> + BUILD_BUG_ON(__alignof__(struct bpf_iter_process_kern) !=
> + __alignof__(struct bpf_iter_process));
> +
> + rcu_read_lock();
> + kit->tsk = &init_task;
> + return 0;
> +}
> +
> +__bpf_kfunc struct task_struct *bpf_iter_process_next(struct bpf_iter_process *it)
> +{
> + struct bpf_iter_process_kern *kit = (void *)it;
> +
> + kit->tsk = next_task(kit->tsk);
> +
> + return kit->tsk == &init_task ? NULL : kit->tsk;
> +}
> +
> +__bpf_kfunc void bpf_iter_process_destroy(struct bpf_iter_process *it)
> +{
> + rcu_read_unlock();
> +}
This iter can be used in all ctx-s which is nice, but let's
make the verifier enforce rcu_read_lock/unlock done by bpf prog
instead of doing in the ctor/dtor of iter, since
in sleepable progs the verifier won't recognize that body is RCU CS.
We'd need to teach the verifier to allow bpf_iter_process_new()
inside in_rcu_cs() and make sure there is no rcu_read_unlock
while BPF_ITER_STATE_ACTIVE.
bpf_iter_process_destroy() would become a nop.
