Merge branch 'bpf-tracepoints'

Alexei Starovoitov says:

====================
allow bpf attach to tracepoints

Hi Steven, Peter,

v1->v2: addressed Peter's comments:
- fixed wording in patch 1, added ack
- refactored 2nd patch into 3:
2/10 remove unused __perf_addr macro which frees up
an argument in perf_trace_buf_submit
3/10 split perf_trace_buf_prepare into alloc and update parts, so that bpf
programs don't have to pay performance penalty for update of struct trace_entry
which is not going to be accessed by bpf
4/10 actual addition of bpf filter to perf tracepoint handler is now trivial
and bpf prog can be used as proper filter of tracepoints

v1 cover:
last time we discussed bpf+tracepoints it was a year ago [1] and the reason
we didn't proceed with that approach was that bpf would make arguments
arg1, arg2 to trace_xx(arg1, arg2) call to be exposed to bpf program
and that was considered unnecessary extension of abi. Back then I wanted
to avoid the cost of buffer alloc and field assign part in all
of the tracepoints, but looks like when optimized the cost is acceptable.
So this new apporach doesn't expose any new abi to bpf program.
The program is looking at tracepoint fields after they were copied
by perf_trace_xx() and described in /sys/kernel/debug/tracing/events/xxx/format
We made a tool [2] that takes arguments from /sys/.../format and works as:
$ tplist.py -v random:urandom_read
    int got_bits;
    int pool_left;
    int input_left;
Then these fields can be copy-pasted into bpf program like:
struct urandom_read {
    __u64 hidden_pad;
    int got_bits;
    int pool_left;
    int input_left;
};
and the program can use it:
SEC("tracepoint/random/urandom_read")
int bpf_prog(struct urandom_read *ctx)
{
    return ctx->pool_left > 0 ? 1 : 0;
}
This way the program can access tracepoint fields faster than
equivalent bpf+kprobe program, which is the main goal of these patches.

Patch 1-4 are simple changes in perf core side, please review.
I'd like to take the whole set via net-next tree, since the rest of
the patches might conflict with other bpf work going on in net-next
and we want to avoid cross-tree merge conflicts.
Alternatively we can put patches 1-4 into both tip and net-next.

Patch 9 is an example of access to tracepoint fields from bpf prog.
Patch 10 is a micro benchmark for bpf+kprobe vs bpf+tracepoint.

Note that for actual tracing tools the user doesn't need to
run tplist.py and copy-paste fields manually. The tools do it
automatically. Like argdist tool [3] can be used as:
$ argdist -H 't:block:block_rq_complete():u32:nr_sector'
where 'nr_sector' is name of tracepoint field taken from
/sys/kernel/debug/tracing/events/block/block_rq_complete/format
and appropriate bpf program is generated on the fly.

[1] http://thread.gmane.org/gmane.linux.kernel.api/8127/focus=8165
[2] https://github.com/iovisor/bcc/blob/master/tools/tplist.py
[3] https://github.com/iovisor/bcc/blob/master/tools/argdist.py
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

9 files changed, 165 insertions, 41 deletions

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 499d9e933f8e..35114725cf30 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -116,7 +116,7 @@ free_smap:
 	return ERR_PTR(err);
 }
 
-static u64 bpf_get_stackid(u64 r1, u64 r2, u64 flags, u64 r4, u64 r5)
+u64 bpf_get_stackid(u64 r1, u64 r2, u64 flags, u64 r4, u64 r5)
 {
 	struct pt_regs *regs = (struct pt_regs *) (long) r1;
 	struct bpf_map *map = (struct bpf_map *) (long) r2;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2e08f8e9b771..58792fed5678 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -652,8 +652,12 @@ static int check_ctx_access(struct verifier_env *env, int off, int size,
 			    enum bpf_access_type t)
 {
 	if (env->prog->aux->ops->is_valid_access &&
-	    env->prog->aux->ops->is_valid_access(off, size, t))
+	    env->prog->aux->ops->is_valid_access(off, size, t)) {
+		/* remember the offset of last byte accessed in ctx */
+		if (env->prog->aux->max_ctx_offset < off + size)
+			env->prog->aux->max_ctx_offset = off + size;
 		return 0;
+	}
 
 	verbose("invalid bpf_context access off=%d size=%d\n", off, size);
 	return -EACCES;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index de24fbce5277..9a01019ff7c8 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6725,12 +6725,13 @@ int perf_swevent_get_recursion_context(void)
 }
 EXPORT_SYMBOL_GPL(perf_swevent_get_recursion_context);
 
-inline void perf_swevent_put_recursion_context(int rctx)
+void perf_swevent_put_recursion_context(int rctx)
 {
 	struct swevent_htable *swhash = this_cpu_ptr(&swevent_htable);
 
 	put_recursion_context(swhash->recursion, rctx);
 }
+EXPORT_SYMBOL_GPL(perf_swevent_put_recursion_context);
 
 void ___perf_sw_event(u32 event_id, u64 nr, struct pt_regs *regs, u64 addr)
 {
@@ -6987,7 +6988,7 @@ static int perf_tp_event_match(struct perf_event *event,
 	return 1;
 }
 
-void perf_tp_event(u64 addr, u64 count, void *record, int entry_size,
+void perf_tp_event(u16 event_type, u64 count, void *record, int entry_size,
 		   struct pt_regs *regs, struct hlist_head *head, int rctx,
 		   struct task_struct *task)
 {
@@ -6999,9 +7000,11 @@ void perf_tp_event(u64 addr, u64 count, void *record, int entry_size,
 		.data = record,
 	};
 
-	perf_sample_data_init(&data, addr, 0);
+	perf_sample_data_init(&data, 0, 0);
 	data.raw = &raw;
 
+	perf_trace_buf_update(record, event_type);
+
 	hlist_for_each_entry_rcu(event, head, hlist_entry) {
 		if (perf_tp_event_match(event, &data, regs))
 			perf_swevent_event(event, count, &data, regs);
@@ -7104,6 +7107,7 @@ static void perf_event_free_filter(struct perf_event *event)
 
 static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
 {
+	bool is_kprobe, is_tracepoint;
 	struct bpf_prog *prog;
 
 	if (event->attr.type != PERF_TYPE_TRACEPOINT)
@@ -7112,20 +7116,31 @@ static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
 	if (event->tp_event->prog)
 		return -EEXIST;
 
-	if (!(event->tp_event->flags & TRACE_EVENT_FL_UKPROBE))
-		/* bpf programs can only be attached to u/kprobes */
+	is_kprobe = event->tp_event->flags & TRACE_EVENT_FL_UKPROBE;
+	is_tracepoint = event->tp_event->flags & TRACE_EVENT_FL_TRACEPOINT;
+	if (!is_kprobe && !is_tracepoint)
+		/* bpf programs can only be attached to u/kprobe or tracepoint */
 		return -EINVAL;
 
 	prog = bpf_prog_get(prog_fd);
 	if (IS_ERR(prog))
 		return PTR_ERR(prog);
 
-	if (prog->type != BPF_PROG_TYPE_KPROBE) {
+	if ((is_kprobe && prog->type != BPF_PROG_TYPE_KPROBE) ||
+	    (is_tracepoint && prog->type != BPF_PROG_TYPE_TRACEPOINT)) {
 		/* valid fd, but invalid bpf program type */
 		bpf_prog_put(prog);
 		return -EINVAL;
 	}
 
+	if (is_tracepoint) {
+		int off = trace_event_get_offsets(event->tp_event);
+
+		if (prog->aux->max_ctx_offset > off) {
+			bpf_prog_put(prog);
+			return -EACCES;
+		}
+	}
 	event->tp_event->prog = prog;
 
 	return 0;
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 3e4ffb3ace5f..413ec5614180 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -268,7 +268,7 @@ static const struct bpf_func_proto bpf_perf_event_output_proto = {
 	.arg5_type	= ARG_CONST_STACK_SIZE,
 };
 
-static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func_id)
+static const struct bpf_func_proto *tracing_func_proto(enum bpf_func_id func_id)
 {
 	switch (func_id) {
 	case BPF_FUNC_map_lookup_elem:
@@ -295,12 +295,20 @@ static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func
 		return &bpf_get_smp_processor_id_proto;
 	case BPF_FUNC_perf_event_read:
 		return &bpf_perf_event_read_proto;
+	default:
+		return NULL;
+	}
+}
+
+static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func_id)
+{
+	switch (func_id) {
 	case BPF_FUNC_perf_event_output:
 		return &bpf_perf_event_output_proto;
 	case BPF_FUNC_get_stackid:
 		return &bpf_get_stackid_proto;
 	default:
-		return NULL;
+		return tracing_func_proto(func_id);
 	}
 }
 
@@ -332,9 +340,82 @@ static struct bpf_prog_type_list kprobe_tl = {
 	.type	= BPF_PROG_TYPE_KPROBE,
 };
 
+static u64 bpf_perf_event_output_tp(u64 r1, u64 r2, u64 index, u64 r4, u64 size)
+{
+	/*
+	 * r1 points to perf tracepoint buffer where first 8 bytes are hidden
+	 * from bpf program and contain a pointer to 'struct pt_regs'. Fetch it
+	 * from there and call the same bpf_perf_event_output() helper
+	 */
+	u64 ctx = *(long *)r1;
+
+	return bpf_perf_event_output(ctx, r2, index, r4, size);
+}
+
+static const struct bpf_func_proto bpf_perf_event_output_proto_tp = {
+	.func		= bpf_perf_event_output_tp,
+	.gpl_only	= true,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_CTX,
+	.arg2_type	= ARG_CONST_MAP_PTR,
+	.arg3_type	= ARG_ANYTHING,
+	.arg4_type	= ARG_PTR_TO_STACK,
+	.arg5_type	= ARG_CONST_STACK_SIZE,
+};
+
+static u64 bpf_get_stackid_tp(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+	u64 ctx = *(long *)r1;
+
+	return bpf_get_stackid(ctx, r2, r3, r4, r5);
+}
+
+static const struct bpf_func_proto bpf_get_stackid_proto_tp = {
+	.func		= bpf_get_stackid_tp,
+	.gpl_only	= true,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_CTX,
+	.arg2_type	= ARG_CONST_MAP_PTR,
+	.arg3_type	= ARG_ANYTHING,
+};
+
+static const struct bpf_func_proto *tp_prog_func_proto(enum bpf_func_id func_id)
+{
+	switch (func_id) {
+	case BPF_FUNC_perf_event_output:
+		return &bpf_perf_event_output_proto_tp;
+	case BPF_FUNC_get_stackid:
+		return &bpf_get_stackid_proto_tp;
+	default:
+		return tracing_func_proto(func_id);
+	}
+}
+
+static bool tp_prog_is_valid_access(int off, int size, enum bpf_access_type type)
+{
+	if (off < sizeof(void *) || off >= PERF_MAX_TRACE_SIZE)
+		return false;
+	if (type != BPF_READ)
+		return false;
+	if (off % size != 0)
+		return false;
+	return true;
+}
+
+static const struct bpf_verifier_ops tracepoint_prog_ops = {
+	.get_func_proto  = tp_prog_func_proto,
+	.is_valid_access = tp_prog_is_valid_access,
+};
+
+static struct bpf_prog_type_list tracepoint_tl = {
+	.ops	= &tracepoint_prog_ops,
+	.type	= BPF_PROG_TYPE_TRACEPOINT,
+};
+
 static int __init register_kprobe_prog_ops(void)
 {
 	bpf_register_prog_type(&kprobe_tl);
+	bpf_register_prog_type(&tracepoint_tl);
 	return 0;
 }
 late_initcall(register_kprobe_prog_ops);
diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 00df25fd86ef..5a927075977f 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -260,42 +260,43 @@ void perf_trace_del(struct perf_event *p_event, int flags)
 	tp_event->class->reg(tp_event, TRACE_REG_PERF_DEL, p_event);
 }
 
-void *perf_trace_buf_prepare(int size, unsigned short type,
-			     struct pt_regs **regs, int *rctxp)
+void *perf_trace_buf_alloc(int size, struct pt_regs **regs, int *rctxp)
 {
-	struct trace_entry *entry;
-	unsigned long flags;
 	char *raw_data;
-	int pc;
+	int rctx;
 
 	BUILD_BUG_ON(PERF_MAX_TRACE_SIZE % sizeof(unsigned long));
 
 	if (WARN_ONCE(size > PERF_MAX_TRACE_SIZE,
-			"perf buffer not large enough"))
+		      "perf buffer not large enough"))
 		return NULL;
 
-	pc = preempt_count();
-
-	*rctxp = perf_swevent_get_recursion_context();
-	if (*rctxp < 0)
+	*rctxp = rctx = perf_swevent_get_recursion_context();
+	if (rctx < 0)
 		return NULL;
 
 	if (regs)
-		*regs = this_cpu_ptr(&__perf_regs[*rctxp]);
-	raw_data = this_cpu_ptr(perf_trace_buf[*rctxp]);
+		*regs = this_cpu_ptr(&__perf_regs[rctx]);
+	raw_data = this_cpu_ptr(perf_trace_buf[rctx]);
 
 	/* zero the dead bytes from align to not leak stack to user */
 	memset(&raw_data[size - sizeof(u64)], 0, sizeof(u64));
+	return raw_data;
+}
+EXPORT_SYMBOL_GPL(perf_trace_buf_alloc);
+NOKPROBE_SYMBOL(perf_trace_buf_alloc);
+
+void perf_trace_buf_update(void *record, u16 type)
+{
+	struct trace_entry *entry = record;
+	int pc = preempt_count();
+	unsigned long flags;
 
-	entry = (struct trace_entry *)raw_data;
 	local_save_flags(flags);
 	tracing_generic_entry_update(entry, flags, pc);
 	entry->type = type;
-
-	return raw_data;
 }
-EXPORT_SYMBOL_GPL(perf_trace_buf_prepare);
-NOKPROBE_SYMBOL(perf_trace_buf_prepare);
+NOKPROBE_SYMBOL(perf_trace_buf_update);
 
 #ifdef CONFIG_FUNCTION_TRACER
 static void
@@ -316,15 +317,16 @@ perf_ftrace_function_call(unsigned long ip, unsigned long parent_ip,
 
 	BUILD_BUG_ON(ENTRY_SIZE > PERF_MAX_TRACE_SIZE);
 
+	memset(&regs, 0, sizeof(regs));
 	perf_fetch_caller_regs(&regs);
 
-	entry = perf_trace_buf_prepare(ENTRY_SIZE, TRACE_FN, NULL, &rctx);
+	entry = perf_trace_buf_alloc(ENTRY_SIZE, NULL, &rctx);
 	if (!entry)
 		return;
 
 	entry->ip = ip;
 	entry->parent_ip = parent_ip;
-	perf_trace_buf_submit(entry, ENTRY_SIZE, rctx, 0,
+	perf_trace_buf_submit(entry, ENTRY_SIZE, rctx, TRACE_FN,
 			      1, &regs, head, NULL);
 
 #undef ENTRY_SIZE
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 05ddc0820771..ced963049e0a 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -204,6 +204,24 @@ static void trace_destroy_fields(struct trace_event_call *call)
 	}
 }
 
+/*
+ * run-time version of trace_event_get_offsets_<call>() that returns the last
+ * accessible offset of trace fields excluding __dynamic_array bytes
+ */
+int trace_event_get_offsets(struct trace_event_call *call)
+{
+	struct ftrace_event_field *tail;
+	struct list_head *head;
+
+	head = trace_get_fields(call);
+	/*
+	 * head->next points to the last field with the largest offset,
+	 * since it was added last by trace_define_field()
+	 */
+	tail = list_first_entry(head, struct ftrace_event_field, link);
+	return tail->offset + tail->size;
+}
+
 int trace_event_raw_init(struct trace_event_call *call)
 {
 	int id;
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 919e0ddd8fcc..5546eec0505f 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -1149,14 +1149,15 @@ kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs)
 	size = ALIGN(__size + sizeof(u32), sizeof(u64));
 	size -= sizeof(u32);
 
-	entry = perf_trace_buf_prepare(size, call->event.type, NULL, &rctx);
+	entry = perf_trace_buf_alloc(size, NULL, &rctx);
 	if (!entry)
 		return;
 
 	entry->ip = (unsigned long)tk->rp.kp.addr;
 	memset(&entry[1], 0, dsize);
 	store_trace_args(sizeof(*entry), &tk->tp, regs, (u8 *)&entry[1], dsize);
-	perf_trace_buf_submit(entry, size, rctx, 0, 1, regs, head, NULL);
+	perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, regs,
+			      head, NULL);
 }
 NOKPROBE_SYMBOL(kprobe_perf_func);
 
@@ -1184,14 +1185,15 @@ kretprobe_perf_func(struct trace_kprobe *tk, struct kretprobe_instance *ri,
 	size = ALIGN(__size + sizeof(u32), sizeof(u64));
 	size -= sizeof(u32);
 
-	entry = perf_trace_buf_prepare(size, call->event.type, NULL, &rctx);
+	entry = perf_trace_buf_alloc(size, NULL, &rctx);
 	if (!entry)
 		return;
 
 	entry->func = (unsigned long)tk->rp.kp.addr;
 	entry->ret_ip = (unsigned long)ri->ret_addr;
 	store_trace_args(sizeof(*entry), &tk->tp, regs, (u8 *)&entry[1], dsize);
-	perf_trace_buf_submit(entry, size, rctx, 0, 1, regs, head, NULL);
+	perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, regs,
+			      head, NULL);
 }
 NOKPROBE_SYMBOL(kretprobe_perf_func);
 #endif	/* CONFIG_PERF_EVENTS */
diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index e78f364cc192..b2b6efc083a4 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -587,15 +587,16 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
 	size = ALIGN(size + sizeof(u32), sizeof(u64));
 	size -= sizeof(u32);
 
-	rec = (struct syscall_trace_enter *)perf_trace_buf_prepare(size,
-				sys_data->enter_event->event.type, NULL, &rctx);
+	rec = perf_trace_buf_alloc(size, NULL, &rctx);
 	if (!rec)
 		return;
 
 	rec->nr = syscall_nr;
 	syscall_get_arguments(current, regs, 0, sys_data->nb_args,
 			       (unsigned long *)&rec->args);
-	perf_trace_buf_submit(rec, size, rctx, 0, 1, regs, head, NULL);
+	perf_trace_buf_submit(rec, size, rctx,
+			      sys_data->enter_event->event.type, 1, regs,
+			      head, NULL);
 }
 
 static int perf_sysenter_enable(struct trace_event_call *call)
@@ -660,14 +661,14 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
 	size = ALIGN(sizeof(*rec) + sizeof(u32), sizeof(u64));
 	size -= sizeof(u32);
 
-	rec = (struct syscall_trace_exit *)perf_trace_buf_prepare(size,
-				sys_data->exit_event->event.type, NULL, &rctx);
+	rec = perf_trace_buf_alloc(size, NULL, &rctx);
 	if (!rec)
 		return;
 
 	rec->nr = syscall_nr;
 	rec->ret = syscall_get_return_value(current, regs);
-	perf_trace_buf_submit(rec, size, rctx, 0, 1, regs, head, NULL);
+	perf_trace_buf_submit(rec, size, rctx, sys_data->exit_event->event.type,
+			      1, regs, head, NULL);
 }
 
 static int perf_sysexit_enable(struct trace_event_call *call)
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 7915142c89e4..c53485441c88 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -1131,7 +1131,7 @@ static void __uprobe_perf_func(struct trace_uprobe *tu,
 	if (hlist_empty(head))
 		goto out;
 
-	entry = perf_trace_buf_prepare(size, call->event.type, NULL, &rctx);
+	entry = perf_trace_buf_alloc(size, NULL, &rctx);
 	if (!entry)
 		goto out;
 
@@ -1152,7 +1152,8 @@ static void __uprobe_perf_func(struct trace_uprobe *tu,
 		memset(data + len, 0, size - esize - len);
 	}
 
-	perf_trace_buf_submit(entry, size, rctx, 0, 1, regs, head, NULL);
+	perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, regs,
+			      head, NULL);
  out:
 	preempt_enable();
 }