On Sat, Mar 02, 2019 at 12:12:57AM +0000, Martin Lau wrote:
> On Fri, Mar 01, 2019 at 10:06:12AM -0800, Javier Honduvilla Coto wrote:
> > From: Javier Honduvilla Coto <javierhond...@gmail.com>
> >
> > This patch adds the bpf_progenyof helper which receives a PID and returns
> > 1 if the process currently being executed is in the process hierarchy
> > including itself or 0 if not.
> >
> > This is very useful in tracing programs when we want to filter by a
> > given PID and all the children it might spawn. The current workarounds
> > most people implement for this purpose have issues:
> >
> > - Attaching to process spawning syscalls and dynamically add those PIDs
> > to some bpf map that would be used to filter is cumbersome and
> > potentially racy.
> > - Unrolling some loop to perform what this helper is doing consumes lots
> > of instructions. That and the impossibility to jump backwards makes it
> > really hard to be correct in really large process chains.
> >
> > Signed-off-by: Javier Honduvilla Coto <javierhond...@gmail.com>
> > ---
> > include/linux/bpf.h | 1 +
> > include/uapi/linux/bpf.h | 11 ++++++++++-
> > kernel/bpf/core.c | 1 +
> > kernel/bpf/helpers.c | 29 +++++++++++++++++++++++++++++
> > kernel/trace/bpf_trace.c | 2 ++
> > 5 files changed, 43 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index de18227b3d95..447395ba202b 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -921,6 +921,7 @@ extern const struct bpf_func_proto
> > bpf_sk_redirect_map_proto;
> > extern const struct bpf_func_proto bpf_spin_lock_proto;
> > extern const struct bpf_func_proto bpf_spin_unlock_proto;
> > extern const struct bpf_func_proto bpf_get_local_storage_proto;
> > +extern const struct bpf_func_proto bpf_progenyof_proto;
> >
> > /* Shared helpers among cBPF and eBPF. */
> > void bpf_user_rnd_init_once(void);
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index bcdd2474eee7..354ec295864c 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -2359,6 +2359,14 @@ union bpf_attr {
> > * Return
> > * A **struct bpf_tcp_sock** pointer on success, or NULL in
> > * case of failure.
> > + *
> > + * int bpf_progenyof(int pid)
> > + * Description
> > + * This helper is useful in programs that want to filter events
> > + * happening to a pid of any of its descendants.
> > + * Return
> > + * 1 if the currently executing process' pid is in the process
> > + * hierarchy of the passed pid. 0 Otherwise.
> > */
> > #define __BPF_FUNC_MAPPER(FN) \
> > FN(unspec), \
> > @@ -2457,7 +2465,8 @@ union bpf_attr {
> > FN(spin_lock), \
> > FN(spin_unlock), \
> > FN(sk_fullsock), \
> > - FN(tcp_sock),
> > + FN(tcp_sock), \
> > + FN(progenyof),
> >
> > /* integer value in 'imm' field of BPF_CALL instruction selects which
> > helper
> > * function eBPF program intends to call
> > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> > index ef88b167959d..69e209fbd128 100644
> > --- a/kernel/bpf/core.c
> > +++ b/kernel/bpf/core.c
> > @@ -2015,6 +2015,7 @@ const struct bpf_func_proto
> > bpf_get_current_uid_gid_proto __weak;
> > const struct bpf_func_proto bpf_get_current_comm_proto __weak;
> > const struct bpf_func_proto bpf_get_current_cgroup_id_proto __weak;
> > const struct bpf_func_proto bpf_get_local_storage_proto __weak;
> > +const struct bpf_func_proto bpf_progenyof_proto __weak;
> >
> > const struct bpf_func_proto * __weak bpf_get_trace_printk_proto(void)
> > {
> > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> > index a411fc17d265..3899787e8dbf 100644
> > --- a/kernel/bpf/helpers.c
> > +++ b/kernel/bpf/helpers.c
> > @@ -18,6 +18,7 @@
> > #include <linux/sched.h>
> > #include <linux/uidgid.h>
> > #include <linux/filter.h>
> > +#include <linux/init_task.h>
> >
> > /* If kernel subsystem is allowing eBPF programs to call this function,
> > * inside its own verifier_ops->get_func_proto() callback it should return
> > @@ -364,3 +365,31 @@ const struct bpf_func_proto
> > bpf_get_local_storage_proto = {
> > };
> > #endif
> > #endif
> > +
> > +BPF_CALL_1(bpf_progenyof, int, pid)
> > +{
> > + int result = 0;
> > + struct task_struct *task = current;
> > +
> > + if (unlikely(!task))
> > + return -EINVAL;
> > +
> > + rcu_read_lock();
> I don't think it is needed. It should already be under rcu_read_lock().
> You may add 'WARN_ON_ONCE(!rcu_read_lock_held());' to be safe,
> like other "bpf_map_xxx_elem()" helpers in the same file.
>
Spot on! Just checked that we are rcu locking in include/linux/bpf.h
being called kernel/trace/bpf_trace.c. Thanks!!
> > + while (task != &init_task) {
> > + if (task->pid == pid) {
> > + result = 1;
> > + break;
> > + }
> > + task = rcu_dereference(task->real_parent);
> > + }
> > + rcu_read_unlock();
> > +
> > + return result;
> > +}
> > +
> > +const struct bpf_func_proto bpf_progenyof_proto = {
> > + .func = bpf_progenyof,
> > + .gpl_only = false,
> > + .ret_type = RET_INTEGER,
> > + .arg1_type = ARG_ANYTHING,
> > +};
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index f1a86a0d881d..8602ae83c799 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -600,6 +600,8 @@ tracing_func_proto(enum bpf_func_id func_id, const
> > struct bpf_prog *prog)
> > return &bpf_get_prandom_u32_proto;
> > case BPF_FUNC_probe_read_str:
> > return &bpf_probe_read_str_proto;
> > + case BPF_FUNC_progenyof:
> > + return &bpf_progenyof_proto;
> > #ifdef CONFIG_CGROUPS
> > case BPF_FUNC_get_current_cgroup_id:
> > return &bpf_get_current_cgroup_id_proto;
> > --
> > 2.17.1
> >
