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Message-ID: <mb61pttdwcj5z.fsf@kernel.org>
Date: Tue, 01 Oct 2024 08:38:16 +0000
From: Puranjay Mohan <puranjay@...nel.org>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
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
Subject: Re: [PATCH bpf-next v2 1/2] bpf: implement bpf_send_signal_remote()
kfunc
Andrii Nakryiko <andrii.nakryiko@...il.com> writes:
> 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)?
Yes, I initially thought of allowing the kfunc to take the union itself
but turns out unions are not supported, so I will just use a cast to put
the value in sival_ptr.
>> +
>> + 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?
I guess we can allow it for all program types.
>
>> +}
>> +
>> +late_initcall(bpf_send_signal_kfuncs_init);
>> --
>> 2.40.1
>>
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