[PATCH RFC v2 net-next 13/16] tracing: allow eBPF programs to be attached to events

[Alexei Starovoitov <ast@plumgrid.com>]

User interface:
fd = open("/sys/kernel/debug/tracing/__event__/filter")

write(fd, "bpf_123")

where 123 is process local FD associated with eBPF program previously loaded.
__event__ is static tracepoint event.
(kprobe events will be supported in the future patches)
Once program is successfully attached to tracepoint event, the tracepoint
will be auto-enabled

close(fd)
auto-disables tracepoint event and detaches eBPF program from it

eBPF programs can call in-kernel helper functions to:
- lookup/update/delete elements in maps
- memcmp
- trace_printk
- load_pointer
- dump_stack

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
---
 include/linux/ftrace_event.h       |    5 +
 include/trace/bpf_trace.h          |   29 +++++
 include/trace/ftrace.h             |   10 ++
 include/uapi/linux/bpf.h           |    5 +
 kernel/trace/Kconfig               |    1 +
 kernel/trace/Makefile              |    1 +
 kernel/trace/bpf_trace.c           |  212 ++++++++++++++++++++++++++++++++++++
 kernel/trace/trace.h               |    3 +
 kernel/trace/trace_events.c        |   36 +++++-
 kernel/trace/trace_events_filter.c |   72 +++++++++++-
 10 files changed, 372 insertions(+), 2 deletions(-)
 create mode 100644 include/trace/bpf_trace.h
 create mode 100644 kernel/trace/bpf_trace.c

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index cff3106ffe2c..de313bd9a434 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -237,6 +237,7 @@ enum {
 	TRACE_EVENT_FL_WAS_ENABLED_BIT,
 	TRACE_EVENT_FL_USE_CALL_FILTER_BIT,
 	TRACE_EVENT_FL_TRACEPOINT_BIT,
+	TRACE_EVENT_FL_BPF_BIT,
 };
 
 /*
@@ -259,6 +260,7 @@ enum {
 	TRACE_EVENT_FL_WAS_ENABLED	= (1 << TRACE_EVENT_FL_WAS_ENABLED_BIT),
 	TRACE_EVENT_FL_USE_CALL_FILTER	= (1 << TRACE_EVENT_FL_USE_CALL_FILTER_BIT),
 	TRACE_EVENT_FL_TRACEPOINT	= (1 << TRACE_EVENT_FL_TRACEPOINT_BIT),
+	TRACE_EVENT_FL_BPF		= (1 << TRACE_EVENT_FL_BPF_BIT),
 };
 
 struct ftrace_event_call {
@@ -536,6 +538,9 @@ event_trigger_unlock_commit_regs(struct ftrace_event_file *file,
 		event_triggers_post_call(file, tt);
 }
 
+struct bpf_context;
+void trace_filter_call_bpf(struct event_filter *filter, struct bpf_context *ctx);
+
 enum {
 	FILTER_OTHER = 0,
 	FILTER_STATIC_STRING,
diff --git a/include/trace/bpf_trace.h b/include/trace/bpf_trace.h
new file mode 100644
index 000000000000..2122437f1317
--- /dev/null
+++ b/include/trace/bpf_trace.h
@@ -0,0 +1,29 @@
+/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+#ifndef _LINUX_KERNEL_BPF_TRACE_H
+#define _LINUX_KERNEL_BPF_TRACE_H
+
+/* For tracing filters save first six arguments of tracepoint events.
+ * On 64-bit architectures argN fields will match one to one to arguments passed
+ * to tracepoint events.
+ * On 32-bit architectures u64 arguments to events will be seen into two
+ * consecutive argN, argN+1 fields. Pointers, u32, u16, u8, bool types will
+ * match one to one
+ */
+struct bpf_context {
+	unsigned long arg1;
+	unsigned long arg2;
+	unsigned long arg3;
+	unsigned long arg4;
+	unsigned long arg5;
+	unsigned long arg6;
+};
+
+/* call from ftrace_raw_event_*() to copy tracepoint arguments into ctx */
+void populate_bpf_context(struct bpf_context *ctx, ...);
+
+#endif /* _LINUX_KERNEL_BPF_TRACE_H */
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 26b4f2e13275..ad4987ac68bb 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -17,6 +17,7 @@
  */
 
 #include <linux/ftrace_event.h>
+#include <trace/bpf_trace.h>
 
 /*
  * DECLARE_EVENT_CLASS can be used to add a generic function
@@ -634,6 +635,15 @@ ftrace_raw_event_##call(void *__data, proto)				\
 	if (ftrace_trigger_soft_disabled(ftrace_file))			\
 		return;							\
 									\
+	if (unlikely(ftrace_file->flags & FTRACE_EVENT_FL_FILTERED) &&	\
+	    unlikely(ftrace_file->event_call->flags & TRACE_EVENT_FL_BPF)) { \
+		struct bpf_context __ctx;				\
+									\
+		populate_bpf_context(&__ctx, args, 0, 0, 0, 0, 0);	\
+		trace_filter_call_bpf(ftrace_file->filter, &__ctx);	\
+		return;							\
+	}								\
+									\
 	__data_size = ftrace_get_offsets_##call(&__data_offsets, args); \
 									\
 	entry = ftrace_event_buffer_reserve(&fbuffer, ftrace_file,	\
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 06e0f63055fb..cedcf9a0db53 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -370,6 +370,7 @@ enum bpf_prog_attributes {
 enum bpf_prog_type {
 	BPF_PROG_TYPE_UNSPEC,
 	BPF_PROG_TYPE_SOCKET_FILTER,
+	BPF_PROG_TYPE_TRACING_FILTER,
 };
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
@@ -380,6 +381,10 @@ enum bpf_func_id {
 	BPF_FUNC_map_lookup_elem, /* void *map_lookup_elem(map_id, void *key) */
 	BPF_FUNC_map_update_elem, /* int map_update_elem(map_id, void *key, void *value) */
 	BPF_FUNC_map_delete_elem, /* int map_delete_elem(map_id, void *key) */
+	BPF_FUNC_load_pointer,    /* void *bpf_load_pointer(void *unsafe_ptr) */
+	BPF_FUNC_memcmp,          /* int bpf_memcmp(void *unsafe_ptr, void *safe_ptr, int size) */
+	BPF_FUNC_dump_stack,      /* void bpf_dump_stack(void) */
+	BPF_FUNC_printk,          /* int bpf_printk(const char *fmt, int fmt_size, ...) */
 	__BPF_FUNC_MAX_ID,
 };
 
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index d4409356f40d..e36d42876634 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -80,6 +80,7 @@ config FTRACE_NMI_ENTER
 
 config EVENT_TRACING
 	select CONTEXT_SWITCH_TRACER
+	depends on NET
 	bool
 
 config CONTEXT_SWITCH_TRACER
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index 2611613f14f1..a0fcfd97101d 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -52,6 +52,7 @@ obj-$(CONFIG_EVENT_TRACING) += trace_event_perf.o
 endif
 obj-$(CONFIG_EVENT_TRACING) += trace_events_filter.o
 obj-$(CONFIG_EVENT_TRACING) += trace_events_trigger.o
+obj-$(CONFIG_EVENT_TRACING) += bpf_trace.o
 obj-$(CONFIG_KPROBE_EVENT) += trace_kprobe.o
 obj-$(CONFIG_TRACEPOINTS) += power-traces.o
 ifeq ($(CONFIG_PM_RUNTIME),y)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
new file mode 100644
index 000000000000..7263491be792
--- /dev/null
+++ b/kernel/trace/bpf_trace.c
@@ -0,0 +1,212 @@
+/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of version 2 of the GNU General Public
+ * License as published by the Free Software Foundation.
+ */
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/bpf.h>
+#include <linux/filter.h>
+#include <linux/uaccess.h>
+#include <trace/bpf_trace.h>
+#include "trace.h"
+
+/* call from ftrace_raw_event_*() to copy tracepoint arguments into ctx */
+void populate_bpf_context(struct bpf_context *ctx, ...)
+{
+	va_list args;
+
+	va_start(args, ctx);
+
+	ctx->arg1 = va_arg(args, unsigned long);
+	ctx->arg2 = va_arg(args, unsigned long);
+	ctx->arg3 = va_arg(args, unsigned long);
+	ctx->arg4 = va_arg(args, unsigned long);
+	ctx->arg5 = va_arg(args, unsigned long);
+	ctx->arg6 = va_arg(args, unsigned long);
+
+	va_end(args);
+}
+EXPORT_SYMBOL_GPL(populate_bpf_context);
+
+/* called from eBPF program with rcu lock held */
+static u64 bpf_load_ptr(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+        void *unsafe_ptr = (void *) r1;
+	void *ptr = NULL;
+
+	probe_kernel_read(&ptr, unsafe_ptr, sizeof(void *));
+	return (u64) (unsigned long) ptr;
+}
+
+static u64 bpf_memcmp(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+        void *unsafe_ptr = (void *) r1;
+	void *safe_ptr = (void *) r2;
+	u32 size = (u32) r3;
+	char buf[64];
+	int err;
+
+	if (size < 64) {
+		err = probe_kernel_read(buf, unsafe_ptr, size);
+		if (err)
+			return err;
+		return memcmp(buf, safe_ptr, size);
+	}
+	return -1;
+}
+
+static u64 bpf_dump_stack(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+	trace_dump_stack(0);
+	return 0;
+}
+
+/* limited printk()
+ * only %d %u %x conversion specifiers allowed
+ */
+static u64 bpf_printk(u64 r1, u64 fmt_size, u64 r3, u64 r4, u64 r5)
+{
+	char *fmt = (char *) r1;
+	int fmt_cnt = 0;
+	int i;
+
+	/* bpf_check() guarantees that fmt points to bpf program stack and
+	 * fmt_size bytes of it were initialized by bpf program
+	 */
+	if (fmt[fmt_size - 1] != 0)
+		return -EINVAL;
+
+	/* check format string for allowed specifiers */
+	for (i = 0; i < fmt_size; i++)
+		if (fmt[i] == '%') {
+			if (i + 1 >= fmt_size)
+				return -EINVAL;
+			if (fmt[i + 1] != 'd' && fmt[i + 1] != 'u' &&
+			    fmt[i + 1] != 'x')
+				return -EINVAL;
+			fmt_cnt++;
+		}
+
+	if (fmt_cnt > 3)
+		return -EINVAL;
+
+	return __trace_printk((unsigned long) __builtin_return_address(3), fmt,
+			      (u32) r3, (u32) r4, (u32) r5);
+}
+
+static struct bpf_func_proto tracing_filter_funcs[] = {
+	[BPF_FUNC_load_pointer] = {
+		.func = bpf_load_ptr,
+		.gpl_only = true,
+		.ret_type = RET_INTEGER,
+	},
+	[BPF_FUNC_memcmp] = {
+		.func = bpf_memcmp,
+		.gpl_only = false,
+		.ret_type = RET_INTEGER,
+		.arg1_type = ARG_ANYTHING,
+		.arg2_type = ARG_PTR_TO_STACK,
+		.arg3_type = ARG_CONST_STACK_SIZE,
+	},
+	[BPF_FUNC_dump_stack] = {
+		.func = bpf_dump_stack,
+		.gpl_only = false,
+		.ret_type = RET_VOID,
+	},
+	[BPF_FUNC_printk] = {
+		.func = bpf_printk,
+		.gpl_only = true,
+		.ret_type = RET_INTEGER,
+		.arg1_type = ARG_PTR_TO_STACK,
+		.arg2_type = ARG_CONST_STACK_SIZE,
+	},
+	[BPF_FUNC_map_lookup_elem] = {
+		.func = bpf_map_lookup_elem,
+		.gpl_only = false,
+		.ret_type = RET_PTR_TO_MAP_OR_NULL,
+		.arg1_type = ARG_CONST_MAP_ID,
+		.arg2_type = ARG_PTR_TO_MAP_KEY,
+	},
+	[BPF_FUNC_map_update_elem] = {
+		.func = bpf_map_update_elem,
+		.gpl_only = false,
+		.ret_type = RET_INTEGER,
+		.arg1_type = ARG_CONST_MAP_ID,
+		.arg2_type = ARG_PTR_TO_MAP_KEY,
+		.arg3_type = ARG_PTR_TO_MAP_VALUE,
+	},
+	[BPF_FUNC_map_delete_elem] = {
+		.func = bpf_map_delete_elem,
+		.gpl_only = false,
+		.ret_type = RET_INTEGER,
+		.arg1_type = ARG_CONST_MAP_ID,
+		.arg2_type = ARG_PTR_TO_MAP_KEY,
+	},
+};
+
+static const struct bpf_func_proto *tracing_filter_func_proto(enum bpf_func_id func_id)
+{
+	if (func_id < 0 || func_id >= ARRAY_SIZE(tracing_filter_funcs))
+		return NULL;
+	return &tracing_filter_funcs[func_id];
+}
+
+static const struct bpf_context_access {
+	int size;
+	enum bpf_access_type type;
+} tracing_filter_ctx_access[] = {
+	[offsetof(struct bpf_context, arg1)] = {
+		FIELD_SIZEOF(struct bpf_context, arg1),
+		BPF_READ
+	},
+	[offsetof(struct bpf_context, arg2)] = {
+		FIELD_SIZEOF(struct bpf_context, arg2),
+		BPF_READ
+	},
+	[offsetof(struct bpf_context, arg3)] = {
+		FIELD_SIZEOF(struct bpf_context, arg3),
+		BPF_READ
+	},
+	[offsetof(struct bpf_context, arg4)] = {
+		FIELD_SIZEOF(struct bpf_context, arg4),
+		BPF_READ
+	},
+	[offsetof(struct bpf_context, arg5)] = {
+		FIELD_SIZEOF(struct bpf_context, arg5),
+		BPF_READ
+	},
+};
+
+static bool tracing_filter_is_valid_access(int off, int size, enum bpf_access_type type)
+{
+	const struct bpf_context_access *access;
+
+	if (off < 0 || off >= ARRAY_SIZE(tracing_filter_ctx_access))
+		return false;
+
+	access = &tracing_filter_ctx_access[off];
+	if (access->size == size && (access->type & type))
+		return true;
+
+	return false;
+}
+
+static struct bpf_verifier_ops tracing_filter_ops = {
+	.get_func_proto = tracing_filter_func_proto,
+	.is_valid_access = tracing_filter_is_valid_access,
+};
+
+static struct bpf_prog_type_list tl = {
+	.ops = &tracing_filter_ops,
+	.type = BPF_PROG_TYPE_TRACING_FILTER,
+};
+
+static int __init register_tracing_filter_ops(void)
+{
+	bpf_register_prog_type(&tl);
+	return 0;
+}
+late_initcall(register_tracing_filter_ops);
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 9258f5a815db..bb7c6a19ead5 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -984,12 +984,15 @@ struct ftrace_event_field {
 	int			is_signed;
 };
 
+struct sk_filter;
+
 struct event_filter {
 	int			n_preds;	/* Number assigned */
 	int			a_preds;	/* allocated */
 	struct filter_pred	*preds;
 	struct filter_pred	*root;
 	char			*filter_string;
+	struct sk_filter	*prog;
 };
 
 struct event_subsystem {
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index f99e0b3bca8c..de79c27a0a42 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1048,6 +1048,26 @@ event_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
 	return r;
 }
 
+static int event_filter_release(struct inode *inode, struct file *filp)
+{
+	struct ftrace_event_file *file;
+	char buf[2] = "0";
+
+	mutex_lock(&event_mutex);
+	file = event_file_data(filp);
+	if (file) {
+		if (file->event_call->flags & TRACE_EVENT_FL_BPF) {
+			/* auto-disable the filter */
+			ftrace_event_enable_disable(file, 0);
+
+			/* if BPF filter was used, clear it on fd close */
+			apply_event_filter(file, buf);
+		}
+	}
+	mutex_unlock(&event_mutex);
+	return 0;
+}
+
 static ssize_t
 event_filter_write(struct file *filp, const char __user *ubuf, size_t cnt,
 		   loff_t *ppos)
@@ -1071,10 +1091,23 @@ event_filter_write(struct file *filp, const char __user *ubuf, size_t cnt,
 
 	mutex_lock(&event_mutex);
 	file = event_file_data(filp);
-	if (file)
+	if (file) {
 		err = apply_event_filter(file, buf);
+		if (!err && file->event_call->flags & TRACE_EVENT_FL_BPF)
+			/* once filter is applied, auto-enable it */
+			ftrace_event_enable_disable(file, 1);
+	}
+
 	mutex_unlock(&event_mutex);
 
+	if (file && file->event_call->flags & TRACE_EVENT_FL_BPF) {
+		/*
+		 * allocate per-cpu printk buffers, since eBPF program
+		 * might be calling bpf_trace_printk
+		 */
+		trace_printk_init_buffers();
+	}
+
 	free_page((unsigned long) buf);
 	if (err < 0)
 		return err;
@@ -1325,6 +1358,7 @@ static const struct file_operations ftrace_event_filter_fops = {
 	.open = tracing_open_generic,
 	.read = event_filter_read,
 	.write = event_filter_write,
+	.release = event_filter_release,
 	.llseek = default_llseek,
 };
 
diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 8a8631926a07..a27526fae0fe 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -23,6 +23,9 @@
 #include <linux/mutex.h>
 #include <linux/perf_event.h>
 #include <linux/slab.h>
+#include <linux/bpf.h>
+#include <trace/bpf_trace.h>
+#include <linux/filter.h>
 
 #include "trace.h"
 #include "trace_output.h"
@@ -535,6 +538,16 @@ static int filter_match_preds_cb(enum move_type move, struct filter_pred *pred,
 	return WALK_PRED_DEFAULT;
 }
 
+void trace_filter_call_bpf(struct event_filter *filter, struct bpf_context *ctx)
+{
+	BUG_ON(!filter || !filter->prog);
+
+	rcu_read_lock();
+	SK_RUN_FILTER(filter->prog, (void *) ctx);
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL_GPL(trace_filter_call_bpf);
+
 /* return 1 if event matches, 0 otherwise (discard) */
 int filter_match_preds(struct event_filter *filter, void *rec)
 {
@@ -794,6 +807,8 @@ static void __free_filter(struct event_filter *filter)
 	if (!filter)
 		return;
 
+	if (filter->prog)
+		sk_unattached_filter_destroy(filter->prog);
 	__free_preds(filter);
 	kfree(filter->filter_string);
 	kfree(filter);
@@ -1898,6 +1913,48 @@ static int create_filter_start(char *filter_str, bool set_str,
 	return err;
 }
 
+static int create_filter_bpf(char *filter_str, struct event_filter **filterp)
+{
+	struct event_filter *filter;
+	struct sk_filter *prog;
+	long ufd;
+	int err = 0;
+
+	*filterp = NULL;
+
+	filter = __alloc_filter();
+	if (!filter)
+		return -ENOMEM;
+
+	err = replace_filter_string(filter, filter_str);
+	if (err)
+		goto free_filter;
+
+	err = kstrtol(filter_str + 4, 0, &ufd);
+	if (err)
+		goto free_filter;
+
+	err = -ESRCH;
+	prog = bpf_prog_get(ufd);
+	if (!prog)
+		goto free_filter;
+
+	filter->prog = prog;
+
+	err = -EINVAL;
+	if (prog->info->prog_type != BPF_PROG_TYPE_TRACING_FILTER)
+		/* prog_id is valid, but it's not a tracing filter program */
+		goto free_filter;
+
+	*filterp = filter;
+
+	return 0;
+
+free_filter:
+	__free_filter(filter);
+	return err;
+}
+
 static void create_filter_finish(struct filter_parse_state *ps)
 {
 	if (ps) {
@@ -2007,7 +2064,20 @@ int apply_event_filter(struct ftrace_event_file *file, char *filter_string)
 		return 0;
 	}
 
-	err = create_filter(call, filter_string, true, &filter);
+	/*
+	 * 'bpf_123' string is a request to attach eBPF program with id == 123
+	 * also accept 'bpf 123', 'bpf.123', 'bpf-123' variants
+	 */
+	if (memcmp(filter_string, "bpf", 3) == 0 && filter_string[3] != 0 &&
+	    filter_string[4] != 0) {
+		err = create_filter_bpf(filter_string, &filter);
+		if (!err)
+			call->flags |= TRACE_EVENT_FL_BPF;
+	} else {
+		err = create_filter(call, filter_string, true, &filter);
+		if (!err)
+			call->flags &= ~TRACE_EVENT_FL_BPF;
+	}
 
 	/*
 	 * Always swap the call filter with the new filter
-- 
1.7.9.5