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Message-ID: <CAEf4Bzac9hbk7vgKETsS56iqy9Did8Zq6HJkQha4ksCE-Fk-2A@mail.gmail.com>
Date: Mon, 30 Sep 2024 14:52:18 -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 Mon, Sep 30, 2024 at 2:48 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> 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)
Bikeshedding here a bit, but would bpf_send_signal_task() be a better
name for something that accepts task_struct?
> > +{
> > + 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)?
Seems like Alexei already suggested that on patch #2, I support the request.
>
> > +
> > + 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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