[PATCH v9 tip 3/9] tracing: attach BPF programs to kprobes

Alexei Starovoitov
2015-03-20T23:32:58Z

User interface:
struct perf_event_attr attr = {.type = PERF_TYPE_TRACEPOINT, .config = event_id, ...};
event_fd = perf_event_open(&attr,...);
ioctl(event_fd, PERF_EVENT_IOC_SET_BPF, prog_fd);

prog_fd is a file descriptor associated with BPF program previously loaded.
event_id is an ID of created kprobe

close(event_fd) - automatically detaches BPF program from it

BPF programs can call in-kernel helper functions to:
- lookup/update/delete elements in maps
- probe_read - wraper of probe_kernel_read() used to access any kernel
data structures

BPF programs receive 'struct pt_regs *' as an input
('struct pt_regs' is architecture dependent)
and return 0 to ignore the event and 1 to store kprobe event into ring buffer.

Note, kprobes are _not_ a stable kernel ABI, so bpf programs attached to
kprobes must be recompiled for every kernel version and user must supply correct
LINUX_VERSION_CODE in attr.kern_version during bpf_prog_load() call.

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
---
include/linux/ftrace_event.h | 11 ++++
include/uapi/linux/bpf.h | 3 +
include/uapi/linux/perf_event.h | 1 +
kernel/bpf/syscall.c | 7 ++-
kernel/events/core.c | 59 ++++++++++++++++++
kernel/trace/Makefile | 1 +
kernel/trace/bpf_trace.c | 130 +++++++++++++++++++++++++++++++++++++++
kernel/trace/trace_kprobe.c | 8 +++
8 files changed, 219 insertions(+), 1 deletion(-)
create mode 100644 kernel/trace/bpf_trace.c

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 77325e1a1816..0aa535bc9f05 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -13,6 +13,7 @@ struct trace_array;
struct trace_buffer;
struct tracer;
struct dentry;
+struct bpf_prog;

struct trace_print_flags {
unsigned long mask;
@@ -306,6 +307,7 @@ struct ftrace_event_call {
#ifdef CONFIG_PERF_EVENTS
int perf_refcount;
struct hlist_head __percpu *perf_events;
+ struct bpf_prog *prog;

int (*perf_perm)(struct ftrace_event_call *,
struct perf_event *);
@@ -551,6 +553,15 @@ event_trigger_unlock_commit_regs(struct ftrace_event_file *file,
event_triggers_post_call(file, tt);
}

+#ifdef CONFIG_BPF_SYSCALL
+unsigned int trace_call_bpf(struct bpf_prog *prog, void *ctx);
+#else
+static inline unsigned int trace_call_bpf(struct bpf_prog *prog, void *ctx)
+{
+ return 1;
+}
+#endif
+
enum {
FILTER_OTHER = 0,
FILTER_STATIC_STRING,
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 45da7ec7d274..b2948feeb70b 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -118,6 +118,7 @@ enum bpf_map_type {
enum bpf_prog_type {
BPF_PROG_TYPE_UNSPEC,
BPF_PROG_TYPE_SOCKET_FILTER,
+ BPF_PROG_TYPE_KPROBE,
};

/* flags for BPF_MAP_UPDATE_ELEM command */
@@ -151,6 +152,7 @@ union bpf_attr {
__u32 log_level; /* verbosity level of verifier */
__u32 log_size; /* size of user buffer */
__aligned_u64 log_buf; /* user supplied buffer */
+ __u32 kern_version; /* checked when prog_type=kprobe */
};
} __attribute__((aligned(8)));

@@ -162,6 +164,7 @@ enum bpf_func_id {
BPF_FUNC_map_lookup_elem, /* void *map_lookup_elem(&map, &key) */
BPF_FUNC_map_update_elem, /* int map_update_elem(&map, &key, &value, flags) */
BPF_FUNC_map_delete_elem, /* int map_delete_elem(&map, &key) */
+ BPF_FUNC_probe_read, /* int bpf_probe_read(void *dst, int size, void *src) */
__BPF_FUNC_MAX_ID,
};

diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 3c8b45de57ec..ad4dade2a502 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -382,6 +382,7 @@ struct perf_event_attr {
#define PERF_EVENT_IOC_SET_OUTPUT _IO ('$', 5)
#define PERF_EVENT_IOC_SET_FILTER _IOW('$', 6, char *)
#define PERF_EVENT_IOC_ID _IOR('$', 7, __u64 *)
+#define PERF_EVENT_IOC_SET_BPF _IOW('$', 8, __u32)

enum perf_event_ioc_flags {
PERF_IOC_FLAG_GROUP = 1U << 0,
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 536edc2be307..504c10b990ef 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -16,6 +16,7 @@
#include <linux/file.h>
#include <linux/license.h>
#include <linux/filter.h>
+#include <linux/version.h>

static LIST_HEAD(bpf_map_types);

@@ -467,7 +468,7 @@ struct bpf_prog *bpf_prog_get(u32 ufd)
}

/* last field in 'union bpf_attr' used by this command */
-#define BPF_PROG_LOAD_LAST_FIELD log_buf
+#define BPF_PROG_LOAD_LAST_FIELD kern_version

static int bpf_prog_load(union bpf_attr *attr)
{
@@ -492,6 +493,10 @@ static int bpf_prog_load(union bpf_attr *attr)
if (attr->insn_cnt >= BPF_MAXINSNS)
return -EINVAL;

+ if (type == BPF_PROG_TYPE_KPROBE &&
+ attr->kern_version != LINUX_VERSION_CODE)
+ return -EINVAL;
+
/* plain bpf_prog allocation */
prog = bpf_prog_alloc(bpf_prog_size(attr->insn_cnt), GFP_USER);
if (!prog)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 2709063eb26b..3a45e7f6b2df 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -42,6 +42,8 @@
#include <linux/module.h>
#include <linux/mman.h>
#include <linux/compat.h>
+#include <linux/bpf.h>
+#include <linux/filter.h>

#include "internal.h"

@@ -3402,6 +3404,7 @@ errout:
}

static void perf_event_free_filter(struct perf_event *event);
+static void perf_event_free_bpf_prog(struct perf_event *event);

static void free_event_rcu(struct rcu_head *head)
{
@@ -3411,6 +3414,7 @@ static void free_event_rcu(struct rcu_head *head)
if (event->ns)
put_pid_ns(event->ns);
perf_event_free_filter(event);
+ perf_event_free_bpf_prog(event);
kfree(event);
}

@@ -3923,6 +3927,7 @@ static inline int perf_fget_light(int fd, struct fd *p)
static int perf_event_set_output(struct perf_event *event,
struct perf_event *output_event);
static int perf_event_set_filter(struct perf_event *event, void __user *arg);
+static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd);

static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned long arg)
{
@@ -3976,6 +3981,9 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon
case PERF_EVENT_IOC_SET_FILTER:
return perf_event_set_filter(event, (void __user *)arg);

+ case PERF_EVENT_IOC_SET_BPF:
+ return perf_event_set_bpf_prog(event, arg);
+
default:
return -ENOTTY;
}
@@ -6436,6 +6444,49 @@ static void perf_event_free_filter(struct perf_event *event)
ftrace_profile_free_filter(event);
}

+static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
+{
+ struct bpf_prog *prog;
+
+ if (event->attr.type != PERF_TYPE_TRACEPOINT)
+ return -EINVAL;
+
+ if (event->tp_event->prog)
+ return -EEXIST;
+
+ if (!(event->tp_event->flags & TRACE_EVENT_FL_KPROBE))
+ /* bpf programs can only be attached to kprobes */
+ return -EINVAL;
+
+ prog = bpf_prog_get(prog_fd);
+ if (IS_ERR(prog))
+ return PTR_ERR(prog);
+
+ if (prog->aux->prog_type != BPF_PROG_TYPE_KPROBE) {
+ /* valid fd, but invalid bpf program type */
+ bpf_prog_put(prog);
+ return -EINVAL;
+ }
+
+ event->tp_event->prog = prog;
+
+ return 0;
+}
+
+static void perf_event_free_bpf_prog(struct perf_event *event)
+{
+ struct bpf_prog *prog;
+
+ if (!event->tp_event)
+ return;
+
+ prog = event->tp_event->prog;
+ if (prog) {
+ event->tp_event->prog = NULL;
+ bpf_prog_put(prog);
+ }
+}
+
#else

static inline void perf_tp_register(void)
@@ -6451,6 +6502,14 @@ static void perf_event_free_filter(struct perf_event *event)
{
}

+static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
+{
+ return -ENOENT;
+}
+
+static void perf_event_free_bpf_prog(struct perf_event *event)
+{
+}
#endif /* CONFIG_EVENT_TRACING */

#ifdef CONFIG_HAVE_HW_BREAKPOINT
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index 98f26588255e..c575a300103b 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -53,6 +53,7 @@ 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_BPF_SYSCALL) += bpf_trace.o
obj-$(CONFIG_KPROBE_EVENT) += trace_kprobe.o
obj-$(CONFIG_TRACEPOINTS) += power-traces.o
ifeq ($(CONFIG_PM),y)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
new file mode 100644
index 000000000000..10ac48da4bb7
--- /dev/null
+++ b/kernel/trace/bpf_trace.c
@@ -0,0 +1,130 @@
+/* Copyright (c) 2011-2015 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.h"
+
+static DEFINE_PER_CPU(int, bpf_prog_active);
+
+/**
+ * trace_call_bpf - invoke BPF program
+ * @prog: BPF program
+ * @ctx: opaque context pointer
+ *
+ * kprobe handlers execute BPF programs via this helper.
+ * Can be used from static tracepoints in the future.
+ *
+ * Return: BPF programs always return an integer which is interpreted by
+ * kprobe handler as:
+ * 0 - return from kprobe (event is filtered out)
+ * 1 - store kprobe event into ring buffer
+ * Other values are reserved and currently alias to 1
+ */
+unsigned int trace_call_bpf(struct bpf_prog *prog, void *ctx)
+{
+ unsigned int ret;
+
+ if (in_nmi()) /* not supported yet */
+ return 1;
+
+ preempt_disable();
+
+ if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1)) {
+ /*
+ * since some bpf program is already running on this cpu,
+ * don't call into another bpf program (same or different)
+ * and don't send kprobe event into ring-buffer,
+ * so return zero here
+ */
+ ret = 0;
+ goto out;
+ }
+
+ rcu_read_lock();
+ ret = BPF_PROG_RUN(prog, ctx);
+ rcu_read_unlock();
+
+ out:
+ __this_cpu_dec(bpf_prog_active);
+ preempt_enable();
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(trace_call_bpf);
+
+static u64 bpf_probe_read(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+ void *dst = (void *) (long) r1;
+ int size = (int) r2;
+ void *unsafe_ptr = (void *) (long) r3;
+
+ return probe_kernel_read(dst, unsafe_ptr, size);
+}
+
+static const struct bpf_func_proto bpf_probe_read_proto = {
+ .func = bpf_probe_read,
+ .gpl_only = true,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_STACK,
+ .arg2_type = ARG_CONST_STACK_SIZE,
+ .arg3_type = ARG_ANYTHING,
+};
+
+static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func_id)
+{
+ switch (func_id) {
+ case BPF_FUNC_map_lookup_elem:
+ return &bpf_map_lookup_elem_proto;
+ case BPF_FUNC_map_update_elem:
+ return &bpf_map_update_elem_proto;
+ case BPF_FUNC_map_delete_elem:
+ return &bpf_map_delete_elem_proto;
+ case BPF_FUNC_probe_read:
+ return &bpf_probe_read_proto;
+ default:
+ return NULL;
+ }
+}
+
+/* bpf+kprobe programs can access fields of 'struct pt_regs' */
+static bool kprobe_prog_is_valid_access(int off, int size, enum bpf_access_type type)
+{
+ /* check bounds */
+ if (off < 0 || off >= sizeof(struct pt_regs))
+ return false;
+
+ /* only read is allowed */
+ if (type != BPF_READ)
+ return false;
+
+ /* disallow misaligned access */
+ if (off % size != 0)
+ return false;
+
+ return true;
+}
+
+static struct bpf_verifier_ops kprobe_prog_ops = {
+ .get_func_proto = kprobe_prog_func_proto,
+ .is_valid_access = kprobe_prog_is_valid_access,
+};
+
+static struct bpf_prog_type_list kprobe_tl = {
+ .ops = &kprobe_prog_ops,
+ .type = BPF_PROG_TYPE_KPROBE,
+};
+
+static int __init register_kprobe_prog_ops(void)
+{
+ bpf_register_prog_type(&kprobe_tl);
+ return 0;
+}
+late_initcall(register_kprobe_prog_ops);
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 8fa549f6f528..dc3462507d7c 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -1134,11 +1134,15 @@ static void
kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs)
{
struct ftrace_event_call *call = &tk->tp.call;
+ struct bpf_prog *prog = call->prog;
struct kprobe_trace_entry_head *entry;
struct hlist_head *head;
int size, __size, dsize;
int rctx;

+ if (prog && !trace_call_bpf(prog, regs))
+ return;
+
head = this_cpu_ptr(call->perf_events);
if (hlist_empty(head))
return;
@@ -1165,11 +1169,15 @@ kretprobe_perf_func(struct trace_kprobe *tk, struct kretprobe_instance *ri,
struct pt_regs *regs)
{
struct ftrace_event_call *call = &tk->tp.call;
+ struct bpf_prog *prog = call->prog;
struct kretprobe_trace_entry_head *entry;
struct hlist_head *head;
int size, __size, dsize;
int rctx;

+ if (prog && !trace_call_bpf(prog, regs))
+ return;
+
head = this_cpu_ptr(call->perf_events);
if (hlist_empty(head))
return;
--
1.7.9.5