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Message-ID: <20190302000111.xkkpxa3r36qy62rm@kafai-mbp.dhcp.thefacebook.com> Date: Sat, 2 Mar 2019 00:01:14 +0000 From: Martin Lau <kafai@...com> To: Javier Honduvilla Coto <javierhonduco@...com> CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, Yonghong Song <yhs@...com>, Kernel Team <Kernel-team@...com> Subject: Re: [PATCH bpf-next 1/3] bpf: add bpf_progenyof helper On Fri, Mar 01, 2019 at 09:28:39AM -0800, Javier Honduvilla Coto wrote: > On Wed, Feb 27, 2019 at 06:26:41AM +0000, Martin Lau wrote: > > On Tue, Feb 26, 2019 at 02:36:49PM -0800, Javier Honduvilla Coto wrote: > > > This patch adds the bpf_progenyof helper which receives a PID and returns > > What is progenof? > > > > > 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 <javierhonduco@...com> > > > --- > > > include/linux/bpf.h | 1 + > > > include/uapi/linux/bpf.h | 3 ++- > > > kernel/bpf/core.c | 1 + > > > kernel/bpf/helpers.c | 29 +++++++++++++++++++++++++++++ > > > kernel/trace/bpf_trace.c | 2 ++ > > > 5 files changed, 35 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; > > It seems only used in bpf_trace.c. Does it have to be here? > > > > > > > > /* 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..804e4218eb28 100644 > > > --- a/include/uapi/linux/bpf.h > > > +++ b/include/uapi/linux/bpf.h > > > @@ -2457,7 +2457,8 @@ union bpf_attr { > > > FN(spin_lock), \ > > > FN(spin_unlock), \ > > > FN(sk_fullsock), \ > > > - FN(tcp_sock), > > > + FN(tcp_sock), \ > > > + FN(progenyof), > > Please add doc like other helpers do. > > Oops, good catch, thanks! Will send v2 soon!! > > > > > > > > > /* 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)) > > hmm.... Could current be NULL? > > Wasn't sure about this but added as bpf_get_current_pid_tgid, > bpf_get_current_uid_gid, and bpf_get_current_comm check for this. Texted Alexei > about this and he told me this is probably not necessary anymore, but I > guess it doesn't hurt leaving it? > > > > > > + return -EINVAL; > > > + > > > + rcu_read_lock(); > > > + while (task != &init_task) { > > I don't know the details of init_task, so qq: > > Could the passed in "pid" be the init_task->pid? > > If possible, what is the expected "result"? > > > > Yep! init_task doesn't set a pid for what I could see, so I guess it > will be PID=0. The test in the last patch check bpf_progenyof(0) :) > > bpf_progenyof with 0 or 1 will always return 1 the test in patch 3 commit message has this though: "- progenyof(0) == 0" so the intention for progenyof(0) is to always return 0 or 1? A random ps output from my vm: [root@...h-fb-vm1 bpf]# ps -eaf | head -3 UID PID PPID C STIME TTY TIME CMD root 1 0 0 11:45 ? 00:00:12 /sbin/init root 2 0 0 11:45 ? 00:00:00 [kthreadd] I was asking because, after reading the loop, it seems all tasks tracing back to init_task. so my intuitive thinking is progenyof(init_task.pid) should always return 1. If it is otherwise, some comments and doc would be useful to explain why treating init_task.pid differently. > > > > + 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 > > >
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