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@kernel.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;
+
+	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);
+}
+
+late_initcall(bpf_send_signal_kfuncs_init);
-- 
2.40.1

On Thu, Sep 26, 2024 at 4:53 AM Puranjay Mohan <puranjay@kernel.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@kernel.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
>

Andrii Nakryiko <andrii.nakryiko@gmail.com> writes:

> On Thu, Sep 26, 2024 at 4:53 AM Puranjay Mohan <puranjay@kernel.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@kernel.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
>>

On Mon, Sep 30, 2024 at 2:48 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Thu, Sep 26, 2024 at 4:53 AM Puranjay Mohan <puranjay@kernel.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@kernel.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
> >

Andrii Nakryiko <andrii.nakryiko@gmail.com> writes:

> On Mon, Sep 30, 2024 at 2:48 PM Andrii Nakryiko
> <andrii.nakryiko@gmail.com> wrote:
>>
>> On Thu, Sep 26, 2024 at 4:53 AM Puranjay Mohan <puranjay@kernel.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@kernel.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?

I agree, will use that name in the next version.

>> > +{
>> > +       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
>> >

On Thu, Sep 26, 2024 at 4:53 AM Puranjay Mohan <puranjay@kernel.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@kernel.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;
> +
> +       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);

This is very similar with bpf_send_signal_common().
Pls avoid copy paste and share the code instead.

> +}
> +
> +__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);
> +}
> +
> +late_initcall(bpf_send_signal_kfuncs_init);

Let's avoid all this later_init proliferation.
We have way too many of them across the whole kernel.
Reuse one of the existing places and add kfunc there.
With that extra bpf_send_signal_kfunc_set and send_signal_kfunc_ids
won't be necessary.

pw-bot: cr