Message-ID: <CAEf4BzaUq9WqKL1n8uHJQw3hbEFHYS4c3RN7qPWzbtYHzREThw@mail.gmail.com>
Date: Mon, 30 Sep 2024 14:48:55 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Puranjay Mohan <puranjay@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, bpf@...r.kernel.org, linux-kernel@...r.kernel.org, 
	puranjay12@...il.com
Subject: Re: [PATCH bpf-next v2 1/2] bpf: implement bpf_send_signal_remote() kfunc

On Thu, Sep 26, 2024 at 4:53 AM Puranjay Mohan <puranjay@...nel.org> wrote:
>
> Implement bpf_send_signal_remote kfunc that is similar to
> bpf_send_signal_thread and bpf_send_signal helpers  but can be used to
> send signals to other threads and processes. It also supports sending a
> cookie with the signal similar to sigqueue().
>
> If the receiving process establishes a handler for the signal using the
> SA_SIGINFO flag to sigaction(), then it can obtain this cookie via the
> si_value field of the siginfo_t structure passed as the second argument
> to the handler.
>
> Signed-off-by: Puranjay Mohan <puranjay@...nel.org>
> ---
>  kernel/trace/bpf_trace.c | 78 +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 77 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index a582cd25ca876..51b27db1321fc 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -802,6 +802,9 @@ struct send_signal_irq_work {
>         struct task_struct *task;
>         u32 sig;
>         enum pid_type type;
> +       bool is_siginfo;
> +       kernel_siginfo_t info;
> +       int value;
>  };
>
>  static DEFINE_PER_CPU(struct send_signal_irq_work, send_signal_work);
> @@ -811,7 +814,11 @@ static void do_bpf_send_signal(struct irq_work *entry)
>         struct send_signal_irq_work *work;
>
>         work = container_of(entry, struct send_signal_irq_work, irq_work);
> -       group_send_sig_info(work->sig, SEND_SIG_PRIV, work->task, work->type);
> +       if (work->is_siginfo)
> +               group_send_sig_info(work->sig, &work->info, work->task, work->type);
> +       else
> +               group_send_sig_info(work->sig, SEND_SIG_PRIV, work->task, work->type);
> +
>         put_task_struct(work->task);
>  }
>
> @@ -848,6 +855,7 @@ static int bpf_send_signal_common(u32 sig, enum pid_type type)
>                  * irq works get executed.
>                  */
>                 work->task = get_task_struct(current);
> +               work->is_siginfo = false;
>                 work->sig = sig;
>                 work->type = type;
>                 irq_work_queue(&work->irq_work);
> @@ -3484,3 +3492,71 @@ static int __init bpf_kprobe_multi_kfuncs_init(void)
>  }
>
>  late_initcall(bpf_kprobe_multi_kfuncs_init);
> +
> +__bpf_kfunc_start_defs();
> +
> +__bpf_kfunc int bpf_send_signal_remote(struct task_struct *task, int sig, enum pid_type type,
> +                                      int value)
> +{
> +       struct send_signal_irq_work *work = NULL;
> +       kernel_siginfo_t info;
> +
> +       if (type != PIDTYPE_PID && type != PIDTYPE_TGID)
> +               return -EINVAL;
> +       if (unlikely(task->flags & (PF_KTHREAD | PF_EXITING)))
> +               return -EPERM;
> +       if (unlikely(!nmi_uaccess_okay()))
> +               return -EPERM;
> +       /* Task should not be pid=1 to avoid kernel panic. */
> +       if (unlikely(is_global_init(task)))
> +               return -EPERM;
> +
> +       clear_siginfo(&info);
> +       info.si_signo = sig;
> +       info.si_errno = 0;
> +       info.si_code = SI_KERNEL;
> +       info.si_pid = 0;
> +       info.si_uid = 0;
> +       info.si_value.sival_int = value;

It seems like it could be either int sival_int or `void *sival_ptr`,
i.e., it's actually a 64-bit value on 64-bit architectures.

Can we allow passing a full u64 here and assign it to sival_ptr (with a cast)?

> +
> +       if (irqs_disabled()) {
> +               /* Do an early check on signal validity. Otherwise,
> +                * the error is lost in deferred irq_work.
> +                */
> +               if (unlikely(!valid_signal(sig)))
> +                       return -EINVAL;
> +
> +               work = this_cpu_ptr(&send_signal_work);
> +               if (irq_work_is_busy(&work->irq_work))
> +                       return -EBUSY;
> +
> +               work->task = get_task_struct(task);
> +               work->is_siginfo = true;
> +               work->info = info;
> +               work->sig = sig;
> +               work->type = type;
> +               work->value = value;
> +               irq_work_queue(&work->irq_work);
> +               return 0;
> +       }
> +
> +       return group_send_sig_info(sig, &info, task, type);
> +}
> +
> +__bpf_kfunc_end_defs();
> +
> +BTF_KFUNCS_START(send_signal_kfunc_ids)
> +BTF_ID_FLAGS(func, bpf_send_signal_remote, KF_TRUSTED_ARGS)
> +BTF_KFUNCS_END(send_signal_kfunc_ids)
> +
> +static const struct btf_kfunc_id_set bpf_send_signal_kfunc_set = {
> +       .owner = THIS_MODULE,
> +       .set = &send_signal_kfunc_ids,
> +};
> +
> +static int __init bpf_send_signal_kfuncs_init(void)
> +{
> +       return register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &bpf_send_signal_kfunc_set);

let's allow it for other program types (at least kprobes, tracepoints,
raw_tp, etc, etc)? Is there any problem just allowing it for any
program type?


> +}
> +
> +late_initcall(bpf_send_signal_kfuncs_init);
> --
> 2.40.1
>

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